Animal Diversity Non-Chordate Animals:
Supplementary Material
STRUCTURAL ORGANIZATION
In today’s lab, we will review microscope slides and demonstrations on:
1.
Body Symmetry and Bauplan
2.
Cell and tissue organization: germ layers
3.
Body organization: nature of tissue layers and body cavity
4.
Developmental Patterns: Protostomate and Deuterostomate
LABORATORY OBJECTIVES:
The purpose of this set of laboratory exercises is to introduce you to the structure,
and anatomy of basic animal groups that underlie classification:
•
The differences between asymmetric, radial and bilateral symmetry, as well
as spheroid and bi-radial symmetry, and metameric design in a variety of
animals.
•
To recognize germ layers (endoderm, mesoderm and ectoderm) and
identify cell types within them (epithelial, muscle, digestive, etc.).
•
Differences between acoelomate, pseudocoelomate and coelomate body
organization.
Body Plans
1.
Hydra xs – These small tubular creatures are diploblastic, organisms that
have only two distinct germ layers. The outer layer is ectoderm (ecto-outer,
derm-skin). This cell layer gives rise to the epidermis, ectodermal muscles,
nervous system, etc., during development. The inner layer is endoderm (endoinner). This cell layer gives rise to the gastrovascular cavity (the digestive
system) and associated organs and structures during development. Only two
of the phyla that we cover are considered diploblastic - the Cnidarians, which
include sea anemones, coral, and jellyfish, and the Ctenophora, the comb
jellies.
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Body Organization: Tissue Layers and Body Cavity
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Most animals are triploblastic, with body layers composed of ectoderm,
endoderm and a third tissue layer between them. This middle layer is the
mesoderm, a tissue from which muscle and many organ systems arise during
development. Triploblastic animals can be further classified into three basic
plans of body construction, based on whether an organism has an internal body
cavity independent of the gut and on how this cavity (if present) is formed
during embryogenesis.
a. Acoelomate – These animals lack an internal body cavity, that is, the space
between the gut (endoderm) and the outer body wall (ectoderm) is filled with
tissue derived from the embryonic mesoderm.
b. Pseudocoelomate – These animals have a true, fluid filled body cavity,
however the cavity derives from the blastocoel (a space formed during
gastrulation in a developing embryo) and is not lined with mesoderm.
c. Coelomate – These animals have a fluid filled body cavity between the gut
and the musculature of the outer body wall that is completely lined with
mesoderm.
2.
Dugesia xs – Flatworms, like most animals, are triploblastic. The most
primitive, represented by Dugesia, are acoelomate - there is no body cavity
between the gut and the outer body wall. Characteristically, the area lying
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between the outer body wall and the gut of acoelomates is solid mesoderm
tissue. In Dugesia this tissue is referred to as parenchyma.
3.
Ascaris x.s. – is a pseudocoelomate, an example of the worm-like animals with
a “false” body cavity derived from the blastocoel, and a tubular digestive
system. Most of the more complex invertebrates have a true coelom, which is
an internal fluid-filled space completely surrounded by mesoderm, and lined
with a thin membrane called a mesentery.
4.
Lumbricus xs – is a coelomate, and illustrates the basic body design of most
‘higher’ invertebrates, with three cell layers, a tubular digestive system and a
variety of complex organs.
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We will also look at invertebrate development - The true coelomates are
subdivided into two types, based on embryological development. Protostomes
and deuterostomes are distinguished by cell division or cleavage type, coelom
formation and origin of the mouth and anus. The word protostome means “first
mouth” and comes from the fact that these animals have the first opening of the
blastocoel (the blastopore into the archenteron) give rise to the mouth. The
deuterostome “second mouth” never has the mouth originate from the
blastopore. Usually it is the anus that arises from this opening.
DEMONSTRATIONS
We will also have on display a variety of invertebrate phyla for you to see.
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PORIFERA
TAXONOMY:
Phylum Porifera
The sponges
Class Calcarea
Class Hexactinellida
Class Demospongiae
Spicules composed of calcium carbonate.
Spicules composed of silica.
Spicules composed of silica or spongin fibers or both.
In addition to their taxonomic classes, the sponges are organized into three
structural grades of increasing complexity:
Asconoid
The simplest structural grade, comprised of a single chamber
lined with flagellated choanocytes and single exit pore or osculum
(e.g. Leucosolenia).
Syconoid
Sponges with many flagellated canals, but a single osculum (e.g.
Grantia or Scypha).
Leuconoid
Complex sponges with flagellated chambers and numerous
oscula (this is the most common structural grade) (e.g.
Rhabdodermella, commercial sponges).
Sponges are the simplest of all metazoan animals. Neither true tissues nor organs
are present, and the cells show considerable independence. All members of this
phylum are sessile, and exhibit little detectable movement. Primitive sponges may
appear radially symmetrical, but most sponges are asymmetrical in body shape,
being shaped primarily by environmental factors. Except for a single family, the
phylum is entirely marine.
LABORATORY OBJECTIVES:
The purpose of this set of laboratory exercises is to introduce you to the
classification, structure, and anatomy of sponges. In this lab, you should learn:
1. To recognize the classes and structural grades of sponges.
2. The internal anatomy, including cell types, of sponges of each structural grade.
3. The organization and composition of the sponge skeleton.
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EXERCISES:
1.
Leucosolenia, a common asconoid sponge, will serve to illustrate some of the
basic cell types found in sponges. Observe the diagram below, compare this to
the structure and cell types you observe in Grantia, a syconoid sponge, in
exercise 2.
2.
Grantia (also called Scypha), a common syconoid sponge, will serve to
illustrate additional cell types found in sponges. Look at the prepared slide of a
cross section (cs), for the radial canals and their lining of flagellated choanocyte
cells. The beating of the flagellae in these cells creates a water current that
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brings in food particles through the canals from the incurrent pores or ostia.
Each canal empties into the spongocoel in the center, which empties out
through the single osculum. Look at the longitudinal section (ls) slide and see if
you can figure out the overall body design of this sponge.
3.
Spicules (the “skeleton”) - the skeleton of sponges may be made up of spicules
(calcium carbonate or silica), spongin fibers (protein), or both. Refer to page 79
in your text for some basic spicule types. Examine the slide of Grantia spicules
to see the different shapes and how they hold together. On the slide of
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Spongilla gemmules, there can be seen characteristic amphidisc spicules.
What is a gemmule? What role do gemmules play in the life cycle of sponges?
4.
The three classes of sponges are distinguished by the makeup of their
skeleton. “Unknown” pieces of sponge will be made available in the lab for you
to test and identify. First, isolate the spicules by dissolving away proteins and
other organic matter with bleach solution. If no spicules remain, what class
does the sponge belong to? What shape are the spicules? Does this tell you
what class they are? Add acetic acid, which dissolves calcium carbonate. Does
this help you classify the sponge?
DEMONSTRATIONS:
We will have on display a variety of sponges for you to see.
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CNIDARIA AND CTENOPHORA
TAXONOMY:
Phylum Ctenophora The comb jellies.
Phylum Cnidaria
Class Hydrozoa
The hydrozoans, colonial or solitary coelenterates with
the polyp as the predominant form.
Class Scyphozoa
The jelly fish, characterized by the mobile, floating
medusoid form.
Class Cubozoa
The cubomedusae jellyfish, characterized by a cuboid
swimming bell, with four tentacle clusters
Class Anthozoa
The anemones, corals, sea pens, etc., polypoid forms
often with supporting skeletons.
Subclass Octocorallia
(or Alcyonaria) “soft corals” with 8 tentacles.
Subclass Hexacorallia (or Zoantharia) “hard corals” with > 8 tentacles.
Ctenophora is a small phylum of jellyfish-like marine animals, lacking the one
unifying structure of the true jellyfish (cnidoblasts). They are characterized by
possession of their own unique structures, “comb rows,” which are ciliated bands
running along the length of the body, used for locomotion. They also possess two
long tentacles, armed with explosive sticky cells called colloblasts, with which they
capture plankton.
The Cnidaria are the most primitive of all the eumetazoa (true multicellular animals).
Except for a handful of species, the phylum is marine. They are generally radially
symmetrical, and have tentacles armed with exploding cells (cnidoblasts).
Cnidarians are diploblastic (two cell layers), and have a single body cavity with one
opening (the coelenteron). There are two structural forms: the polyp and the
medusa, which may alternate as vegetative and reproductive generations in the
reproductive cycle.
LABORATORY OBJECTIVES:
The purpose of this part of the lab is to introduce you to the diversity, classification,
anatomy, reproduction, and growth of Ctenophora and Cnidaria. Through this part
of the laboratory, you should:
1. Learn to recognize members of the phyla Ctenophora and Cnidaria, the three
main cnidarian classes (Hydrozoa, Scyphozoa, Anthozoa) and the cnidarian
subclasses Octocorallia and Hexacorallia.
2. Learn the anatomy of Pleurobrachia, Hydra, Obelia, Aurelia, Metridium, and
typical soft and hard corals.
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3. Learn the life cycle of Obelia and Aurelia.
EXERCISES:
Phylum Ctenophora
1.
Pleurobrachia is our only example of this phylum. Examine a preserved
specimen in a finger bowl or plastic mount on demonstration. The broader end
contains the mouth. On the aboral end is the apical organ, which is a sensory
structure. From the apical organ extend the eight lines of comb rows. Examine
these under low power and note the length of cilia. On each side of the
specimen the tentacles can sometimes be seen, although in most preserved
specimens these are broken off. The tentacles can be retracted into a sheath,
which will be visible. Can you find the pharynx and various canals of the
gastrovascular cavity?
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Phylum Cnidaria, Class Hydrozoa
2.
Hydra is a solitary, freshwater polyp-type hydrozoan, and is commonly used as
an example of cnidarian anatomy. Place a live specimen in a watch glass, and
study it with the dissecting microscope at low power. They have a basal disc,
which is attached, and at the oral end is the mouth on the hypostome
surrounded by tentacles. Feed a Hydra with some small Daphnia, and watch
the capture and feeding process.
3.
At higher magnification, clusters of stinging cells, the cnidocytes, can be seen.
These cells contain explosive cell organelles called nematocysts, unique to this
phylum. To study nematocysts, place the Hydra on a concavity slide with a
drop of water and a cover glass. Examine the cells with the low power of your
compound microscope, then introduce a drop of 1% acetic acid to the edge of
the cover slip and draw the water through from the other side with a piece of
paper towel. This should cause some of the nematocysts to fire, enabling you
to compare exploded and unexploded cells.
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4.
Study the prepared microscope slides of Hydra under the dissecting scope and
the compound scope to examine the internal anatomy of Hydra. The central,
inner body cavity is the coelenteron or gastrovascular cavity. This cavity is
lined with a layer of cells called the gastrodermis. The outer side of the body is
covered with a layer of cells called the epidermis. Between them is the
transparent, non-cellular layer of mesoglea. The epidermis contains cells that
serve both covering and contraction functions, the epithelio-muscular cells.
The gastrodermis contains cells with several roles called nutritive-muscular
cells. Also between the cell layers is the nerve net of Hydra, but it cannot be
seen well without staining.
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5.
Reproduction - Hydra reproduces sexually or asexually, and it is sometimes
possible to see reproductive structures on prepared slides and live specimens.
Ova are produced in the ovaries, which appear as enlargements lower on the
trunk. Sperm is produced in a testis, higher up on the body. Can you find
ovaries and testes in the same animal?
6.
Obelia is another representative of the Hydrozoa, but unlike Hydra, it is
colonial. Note the tree-like form of the colony and its stem. Is this one organism
or many? How do you know? Examine the prepared slides, and note the
gastrozoids (feeding polyps also called hydranths). Each has tentacles and a
mouth, and is surrounded by a transparent hydrotheca, a continuation of the
perisarc which covers the tissues of the branching hydrorhiza. On some
branches, there are individuals without tentacles - these are gonozoids
(reproductive polyps also called a gonangium). Notice medusa buds attached
to a central blastostyle on the gonangium, all enclosed by a transparent
gonotheca. The life cycle of Obelia illustrates the alternation of polyp and
medusa generations typical of most hydrozoans.
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Phylum Cnidaria, Class Scyphozoa
7.
Observe a medusa of Aurelia, the moonjelly, and examine the convex
exumbrella and concave subumbrella. Aurelia differs from hydrozoan medusae
in canal structure, location of gonads and sense organs. The mouth is
surrounded by oral arms, and opens into the gastrovascular cavity. Notice the
branching of the radial canals which open into the ring canal, and the four
gastric pouches containing the gonads.
8.
Sense organs - examine the demonstration slide and look under the dissecting
scope for the sense organ clusters, called rhopalia. Among the sense organs
are statoliths for balance, and ocelli for light detection (seen at higher mag.).
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9.
Reproduction - a combination of prepared slides and demonstration material
will illustrate the reproductive cycle of Aurelia. The sexes are separate, and
there is alternation of generations. A planula larva hatches from the egg, and
settles to grow into a specialized polyp, called a scyphistosoma. This polyp
divides by strobilization to produce saucer-like structures, which develop into
free-swimming ephyra. The ephyra grow tentacles and slowly mature into
medusoid jellyfish. Adults produce gametes, which fuse to become eggs, and
then planula larvae.
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Phylum Cnidaria, Class Cubozoa
Unfortunately, we have no specimens of this class of jellyfish. They are notorious as
“sea wasps” and are among the most poisonous of cnidarians.
Phylum Cnidaria, Class Anthozoa, Subclass Hexacorallia
10. Metridium is a common sea anemone, and will serve as a representative of its
class. We will have preserved specimens for you to examine. At one end, the
oral disc bears the mouth and is fringed by tentacles. The tentacles are
covered by cilia as well as cnidoblasts. The mouth opens into the pharynx, with
a thickened groove on the sides called a siphonogyph. At the aboral end of the
animal, attaching it to the substrate is the basal disc (pedal disc).
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Phylum Cnidaria, Class Anthozoa, Subclass Octocorallia
12. Examine the demonstrations, living specimens and slides of the members of
this subclass (Renilla - the sea pansy, sea pens, sea fans, gorgonian corals,
etc.). Compare the structure of the hard corals, soft corals, and the anemones.
What are the differences in tentacles and supporting skeleton?
DEMONSTRATIONS:
We will have a number of demonstrations of anemones and corals for you to see.
The most familiar corals are the reef-building (hermatypic) corals, whose calcium
carbonate skeletons create major marine ecosystems in tropical regions. Examine
demonstrations of other hydrozoans. The Portuguese Man-of-War, Physalia, is an
example of a siphonophore - a colonial hydrozoan in which some individuals are
modified as gas-filled floats, while others comprise the tentacles and feeding
apparatus.
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PLATYHELMINTHES AND NEMERTEA
TAXONOMY:
Phylum Platyhelminthes
The flatworms.
Class Turbellaria
Class Cestoda (Cestoidea)
Class Monogenea
Class Trematoda
Subclass Digenea
Phylum Nemertea
The free-living flatworms.
The tapeworms.
Monogenetic flatworms.
The flukes.
The ribbon worms.
Please note, the taxonomic classification of this phylum has been extensively
revised, but we will use the simpler traditional taxa. The Platyhelminthes are dorsoventrally flattened animals with bilateral symmetry, and a primitive, sac-like digestive
system, but lack a respiratory system, or circulatory system. They have flame cells
(protonephridia) which may or may not serve an excretory function.
LABORATORY OBJECTIVES:
Through these exercises you should:
1. Be able to identify members of the three main platyhelminth classes.
2. Know the anatomy and behavior of Dugesia, the common planarian.
3. Know the anatomy and life cycles of the parasitic flatworms – Opisthorchis
(Clonorchis), Fasciola, Schistosoma and Taenia.
EXERCISES:
Phylum Platyhelminthes, Class Turbellaria - flatworms
The free-living flatworms were considered as members of a single class, the
Turbellaria. This group contains many species, and now actually constitutes 3
classes according to some classifications. Turbellaria are characterized by a welldeveloped gastrovascular cavity with a pharynx, a single nervous system with
cephalization, eyespots, and an epidermis with slime glands and explosive
rhabdites.
1. The common planarian Dugesia sp. is abundant under stones in streams. We
have living specimens for you to observe. Notice the general shape, head end
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and gliding movement. The mouth is on the midventral surface, eye spots on
the anteriodorsal.
2.
Feeding. Place fragments of powdered fish food in the dish. When the
planarians begin to feed, gently turn them over and see how the pharynx is
used.
3.
Dugesia anatomy. Examine the planarian whole mount (WM) and cross
section slides. Find the gastrovascular cavity, gut diverticula, parenchyma, and
the various muscle layers. The epidermis of planarians is ciliated on the ventral
side, and contains specialized explosive cells for defense called rhabdites.
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Phylum Platyhelminthes, Class Cestoda – the tapeworms
The cestodes are entirely endoparasitic in vertebrate alimentary canals. They have
completely lost the digestive system and mouth. Growth is by strobilization (the
same process involved in medusae formation in the Scyphozoa).
4.
Taenia, the pork tapeworm is representative of this class, study the slide in the
slide box. Examine the anterior end called the scolex. There are four large
suckers, and several transverse rows of hooks for attachment.
5.
Proglottids of Taenia slide. The tapeworm produces reproductive units called
proglottids by strobilization (budding). Proglottids are hermaphroditic, and male
and female reproductive organs open on one side of the proglottid to the
outside (you may not be able to see all the structures in any one specimen so
look at several if you have to).
a. Examine a mature proglottid (showing the male and female reproductive
systems) and a gravid proglottid (with uterus full of eggs, obscuring other
structures).
1. Male system: The testes are scattered throughout the proglottid. They
connect, forming a sperm duct. The sperm duct empties into a cirrus
(penis) which is within a cirrus sac. The cirrus sac opens into a common
genital atrium, which in turn opens through a gonopore.
2. Female system: Posterior on the slide find the dark stained yolk glands
(vitellaria), the round ovary, the oviduct, and the vagina emptying into the
common genital atrium. In the most mature proglottids, the uterus is
extensively developed and full of eggs.
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Mature Proglottid
Gravid Proglottid
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Phylum Platyhelminthes, Class Monogenea – monogenetic flatworms
Once classified as trematode flukes, this unusual group of primarily ectoparasitic
flatworms is now recognized as its own class. These flatworms are recognized by
their highly specialized posterior attachment organ, called a haptor. Monogeneans
have a single host in their life cycle, and are usually found on the gills or skin of fish
or in the bladders of amphibians. Their larval form is called an oncomiracidium.
Unfortunately, we have no specimens of Monogenea, but hope to in the near
future…
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Phylum Platyhelminthes, Class Trematoda, Subclass Digenea – the flukes
Trematodes are parasitic Platyhelminthes with specialized adhesive organs and an
incomplete digestive system, but without an epidermis. Instead they possess a
tegument, or non-ciliated cytoplasmic syncytium.
By far, the greatest numbers of parasitic flatworms belong to the Subclass Digenea.
Digenetic trematodes require intermediate hosts to complete their development and
frequently have 2-4 such hosts during the life cycle. The adult stage is found in the
primary (or definitive) host and larval forms are found in intermediate (or secondary)
hosts. All digenetic trematodes are endoparasitic and have an anterior oral sucker
and a ventral acetabulum. Most digenetic trematodes are dioecious, with sexual
reproduction occurring through both self- and cross-fertilization. We have slides for
you to observe.
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6.
Fasciola is a good example of a digenetic trematode. Find the oral sucker
enclosing the mouth. The mouth opens into the muscular pharynx which enters
into the two-branched gut. There is also a ventral sucker (acetabulum).
Between the ventral sucker and the mouth is the genital pore (gonopore). The
coiled uterus is usually filled with brownish eggs. The uterus connects to the
ootype, often surrounded by the shell gland (Mehlis’ organ). On the right side is
the branched ovary, the oviduct connects the ovary to the ootype. On the sides
surrounding the intestinal branches are the yolk glands. The yolk ducts also
open into the ootype. In the ootype, eggs and yolk cells are combined and
surrounded by a shell secreted by the Mehlis’ gland before being passed to the
outside, via the uterus. The branched testes lie in the midline of the animal.
Two vas deferens connect the testes to a seminal vesicle: this in turn continues
into the cirrus sac, containing the penis (cirrus) which opens through the
gonopore.
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7.
Opisthorchis (Chlonorchis) sinensis has the same structures but differs by
having the ovary oval in shape, not branched. The ovary empties through the
oviduct, one branch of which leads to the outside (the other branch is joined by
the yolk duct). Almost in the midline of the fluke is a seminal receptacle. The
branched testes lay one behind the other in the posterior half o the fluke.
Review the life cycle of this human parasite in your book, and compare it to that
of other trematodes. You should be familiar with the various life stages
(sporocysts, redia, cercariae) and the associated intermediate and/or definitive
hosts where each of these stages are found.
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Phylum Nemertea (a.k.a. Nemertinea or Rynchocoela) - the ribbon worms
The ribbon worms are important carnivores in intertidal habitats, and are
distinguished by a remarkable proboscis which they use to capture their prey.
Nemertines are triploblastic and bilateral like the Platyhelminthes, but differ from
them in several ways. They have a "through gut" (with a mouth and an anus), a
complete digestive system, a circulatory system, and a series of protonephridia that
serve a true excretory function. In addition, they possess a rynchocoel - a fluid-filled
cavity housing an eversible proboscis. Nemertineans are also much larger than
flatworms; sometimes several meters in length.
The specimens we have on display are from the genus Cerebratulus. On them you
can see the rynchocoel with its proboscis. This specialized organ is everted (turned
inside out) by fluid pressure in the rynchocoel. The body is not segmented; what
you see are the lines of the well-developed circular muscles, which generate the
waves of peristaltic contractions that enable the animals to move.
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PSEUDOCOELOMATES
TAXONOMY:
Phylum Nematoda
Phylum Rotifera
Phylum Gastrotricha
Phylum Acanthocephala
Phylum Nematomorpha
In this lab, we will cover a variety of phyla that have a few characteristics in
common. They are all triploblastic, and all possess a digestive system that passes
through the body instead of a sac-like gut cavity as seen in the coelenterates and
platyhelminths.
Many of these groups were once considered to be joined in the Super-Phylum
Aschelminthes, because they also share a pseudocoelom, or “false” body cavity
derived from a persistent embryonic blastocoel between the endoderm and the
mesoderm. The organs of the digestive tract are separated from the mesoderm and
body wall by this fluid-filled space, which can serve as a hydrostatic skeleton.
However, recent evidence has revealed that not all of these phyla develop the
pseudocoelom in the same manner, and some possess a layered cuticle which is
periodically shed during growth.
LABORATORY OBJECTIVES:
Through these laboratory exercises you should:
1. Be able to recognize representatives of the phyla covered.
2. Be familiar with prominent anatomical features of the Nematoda, and Rotifera,
3. Know the basic external and internal anatomy of the Nematoda representative,
Ascaris,
4. Learn about the life cycles of nematodes and nematomorphs, and how they
differ.
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EXERCISES:
Phylum Nematoda - the roundworms
1.
Ascaris lumbricoides, used as a representative nematode is atypical of the
roundworms because of its larger size. We have preserved specimens (mostly
females) for dissection. The male is slightly smaller than the female, has a
coiled tail, and two spicules, or setae, found at the male anal slit. The female
gonopore is ventral, one-third of the way to the tail.
The mouth, at the anterior end, has a dorsal lip and two lips on each side
below. Because the dorsal lip is wider than the ventral ones, it is possible to
orient the worms dorso-ventrally. On the dorsal lip, there are sensory papillae.
The anus is at the posterior end, of course.
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2.
Examine prepared slides of male and female Ascaris (cs). Can you identify the
body structures on the slide? Where is the pseudocoel on your slide?
Additional slides:
There are several additional slides of well known nematodes for you to observe,
including the dog hookworm (Ancylostoma caninum), the human hookworm (Necator
americanus) and the ubiquitous human pinworm (Enterobius vermicularis).
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3.
Observe prepared slides of Trichinella spiralis, a parasitic nematode found in
uncooked pork. Also in the box is a slide of Anguillula aceti, the vinegar eel. We
may also have live specimens of this species, which lives in spoiled fruit juices and
“mother of vinegar”.
Trichinella spiralis encysted in pig muscle
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PHYLUM ROTIFERA - the rotifers or “wheel animalcules”
These tiny invertebrates are ecologically very important as plankton in freshwater
ecosystems, and are also found living in the interstitial water of mosses and lichens,
and in marine environments.
4.
We have live rotifers to observe. Be sure to note the major structures, and
observe locomotion and feeding. These animals are characterized by the
corona, a rotating, water moving organ distinguished by a “crown” of cilia which
they use to create a current from which food particles are captured. Food
particles are ingested through a mouth located within or beneath the corona.
Food is then macerated in the mastax, a food crushing organ that is quite
visible near the anterior end (an elongate oval structure with seven internal
projections that function as jaws). Although many rotifers are, in a sense,
sessile suspension feeders, they are capable of movement, and move
frequently by simply detaching their anchoring pedal spur (toes) and letting the
ciliary action of the corona pull them along. They have a telescoping body wall,
with longitudinal and circular muscles, which also enables them to move
around. Some species are predatory, and feed on protozoans, and other small
invertebrates (including other rotifers), using their mastax as a raptorial
(grasping) organ.
Representative Rotifers
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Phylum Gastrotricha - the gastrotrichs
These unusual invertebrates are found in both freshwater and marine environments.
5.
We hope to have living specimens of Lepidodermella for you to study. Most
forms are ventrally ciliated, and locomotion is accomplished in a gliding fashion,
aided by muscular movements. Note the forked posterior end. you may want to
use a compound like Protoslo or Planoslo to slow these down, otherwise you
will have trouble keeping them in your field of vision under the microscope. You
should be able to see the cuticular scales, pharynx, intestine, and caudal
adhesive glands.
Representative Gastrotrichs
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Phylum Acanthocephala - the spiny headed worms
These animals are parasites in insects and crustaceans as juveniles, and intestinal
parasites of humans and other vertebrates. The most prominent feature is the spinecovered proboscis (hence the Phylum name, “spiny head”), used as a holdfast
organ. There is no digestive system, as these parasites live in the intestines of their
hosts and absorb food directly through their body wall.
6.
We will have whole mount slides of Acanthocephala, a large intestinal parasite
of vertebrates on the demonstration bench. On the plastic mount you can see
the major anatomical features of the body; the proboscis, neck, and trunk. We
will also have a demonstration slide of the anterior region, allowing a close-up
view of the spiny proboscis.
Representative Acanthocephalans
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Phylum Nematomorpha - the horsehair or whipworms
Adults of the nematomorph worms are free-living, but the juveniles are parasitic in
insects and crustaceans. There are soil dwelling, marine and freshwater species.
Recent studies, using data from embryology, neurobiology, cuticular ultrastructure
and DNA sequencing of nematodes and other phyla, have found similarities that
raise questions about the phylogenetic position of the several pseudocoelomate
phyla. In particular, there has been the suggestion that nematodes are more closely
related to arthropods (insects, spiders, crabs, etc.), and that flatworms are
degenerate forms of “higher” taxa. Examine the diagram on the next page. Based
on what you have learned, what do you think?
44
45
Annelida & Sipuncula
TAXONOMY:
Phylum Annelida
The segmented worms.
Class Polychaeta
Class Clitellata
Subclass Oligochaeta
Subclass Hirudinea
Class Echiura
Phylum Sipuncula
The peanut worms. (demos up Labs 6 & 7)
LABORATORY OBJECTIVES:
Following this laboratory exercise you should:
1. Be able to recognize members of the Phylum Annelida, the two common
annelid classes (Polychaeta and Clitellata), their subclasses and members of
the Phylum Sipuncula.
Annelid body plan
46
EXERCISES:
Class Polychaeta
1.
Nereis – the clam worm. If available, put a live Nereis in a fingerbowl with
ocean water (be careful, they can deliver a strong bite with their jaws). Watch
the walking and swimming motions of Nereis and compare to the earthworm,
and leech. Notice that the peristaltic movements go from tail to head, opposite
from an earthworm.
a. On a preserved Nereis, find the head with 4 pairs of whisker-like cirri and a
long series of parapodia on each side of the body. Find the prostomium,
bearing two pairs of eyes, two small tentacles and two blunt, fleshy palps.
The peristomium (the first somite) bears 4 pairs of cirri. On a live specimen,
note the everted proboscis which bears two or four strong jaws.
2.
b.
Examine demonstrations of other polychaetes. In various species, the head
and parapodia are modified differently, and serve various functions (gills, fans,
food-gathering structures). Examine the variety of species illustrated, and note
the modifications.
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The demos and diagrams above are the sedentary tube-dwelling polychaetes
Arenicola and Amphitrite.
The tube-dwelling worms Chaetopterus and Sabella shown here are filter
feeders.
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Class Clitellata, Subclass Oligochaeta - the earthworms, bristle-footed worms
3.
Earthworm. If available, let a live earthworm crawl in a pan, on a moist towel.
What movements bring about forward motion? Which way does the wave
pass? What muscle systems move with the body contraction? Watch a single
somite in motion. Put an earthworm on some dry paper and listen to the
scratching of the setae; on a glass plate to see if they can still move. Hang an
earthworm loosely over your finger (posterior end up). Stick a small piece of
filter paper (2cm2) on the anterior. Why does the paper move up toward the
tail?
a.
a. On a prepared slide of an earthworm cross section find the outer cuticle and
the epidermis underneath.
Under the epidermis is a layer of circular muscle and under this a layer of
longitudinal muscle. The membrane towards the coelom is the peritoneum.
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CLASS CLITELLATA - Sub-Class HIRUDINEA
4.
Leech. If available, place a live leech on moist filter paper. How does the leech
move about? Why is it impossible for the leech to use peristaltic earthworm
motion? Immerse the leech in fresh water. How does it swim? Compare the
swimming motion with that of a polychaete. Compare the movements of
members of the 3 classes taking into consideration their muscles and
coordination.
5.
External Anatomy. Examine a preserved leech. There is a large posterior
sucker and a smaller anterior one, containing the mouth. There are no setae.
The body is flattened.
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ARTHROPODA and related phyla
TAXONOMY:
Phylum Onychophora
Phylum Tardigrada
(velvet worms or walking worms; a closely related group)
(water bears; a closely related group)
Phylum Arthropoda
Subphylum Trilobitomorpha – trilobites (extinct)
Subphylum Chelicerata
Class Merostomata – Horseshoe crab
Class Pycnogonida - Sea “spiders”
Class Arachnida – Spiders; Scorpions; Ticks & Mites (& others)
Subphylum Mandibulata
Class Myriapoda
Order Chilopoda – Centipedes
Order Diplopoda – Millipedes
Class Insecta
Order Siphonaptera – Fleas
Order Neuroptera – Lacewings
Order Coleoptera - Beetles
Order Hymenoptera – Wasps; Bees; and Ants
Order Isoptera – Termites
Order Homoptera – Cicadas & others
Order Trichoptera – Caddisflies
Order Lepidoptera – Moths & Butterflies
Order Orthoptera – Grasshoppers; Crickets & Locusts
Order Hemiptera – True Bugs
Order Diptera – Flies
Subphylum Mandibulata
Class Crustacea
Subclass Malacostraca
Order Stomatopoda – Mantis shrimp
Order Isopoda
Order Amphipoda – Scuds
Order Decapoda – Shrimps; Lobsters; & Crabs
Subclass Branchiopoda
Order Anostraca – Brine shrimp (Sea Monkeys)
Order Cladocera – Water fleas (e.g. Daphnia)
Subclass Ostracoda – Seed shrimp
Subclass Copepoda
Subclass Cirripedia – Barnacles
The Phylum Arthropoda contains nearly 1 million species (3x as many as all other
animals taken together!). They show incredible diversity in structure, feeding habits,
and habitat utilization. They are highly successful in terms of both numbers of kinds
51
and numbers of individuals. They are united by the following characteristics:
bilateral symmetry, jointed legs, chitinous exoskeleton, open circulatory system,
ventral nerve cord, and the division of the body into distinct regions. We will also
consider two "near arthropod" phyla (Onychophora and Tardigrada), which share
some (but not all) of these characteristics.
LABORATORY OBJECTIVES:
Through these laboratory exercises you should:
1. Be able to identify the arthropod subphyla, classes, subclasses and orders
demonstrated, and the Phyla Onychophora and Tardigrada.
EXERCISES:
Phylum Onychophora - the walking worms
Onychophorans possess features
characteristic of the Phylum Arthopoda, but
also have affinities with the annelids. They
have a soft, chitinous cuticle, and possess
paired appendages that are lobelike, not
jointed. Many consider these animals the
“missing link” between annelids and
arthropods. Our only example is Peripatus, a
tropical onychophoran. We have plastic
mounts and a few preserved specimens.
1.
Examine the external anatomy of
Peripatus or a related genus (see
demonstrations). The head is
indistinct, but has a pair of antennae.
At the base of the antennae are eyes.
On the venter, find the mouth. Inside
the buccal cavity are two hooked jaws.
Posterior of the mouth are two oral
papillae. The trunk bears a series of short legs, each with two claws. The
tracheae of onychophorans open into small spiracular depressions scattered
over the surface. Inside each leg is a nephridium. How do the legs differ from
those of arthropods?
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Phylum Tardigrada - the water bears
Once thought to be arthropods, these tiny animals have a jointed cuticle and 4 pairs
of walking/crawling appendages. They live in interstitial water of soil, mosses,
lichens, as well as freshwater and marine systems. Cryptobiosis (“hidden life”) is an
amazing feature of tardigrade biology, and is an adaptation to deal with temporary
(ephemeral) habitats that dry up and re-hydrate frequently. Some tardigrades have
been known to exist in this arrested state of metabolism for several hundred years!
We hope to have demonstrations of live tardigrades.
Phylum Arthropoda, Subphylum
Trilobitomorpha - the trilobites
The Trilobitomorpha comprised a
group of arthropods that were
dominant throughout the Cambrian
and Ordovician but went extinct by the
end of the Paleozoic. We will have
models on demonstration for you to
examine. They were unique among
the arthropods in that they had no
specialized head appendages. They
had well developed compound eyes.
The mouth was ventral and directed
posteriorly (very similar to a primitive
crustacean). Trilobites were benthic
and planktonic; trophically they were
probably scavengers.
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Phylum Arthropoda, Subphylum Chelicerata - the chelicerates
The chelicerates have two body regions: the prosoma (cephalothorax) and the
opisthosoma (abdomen). They have no antennae; the first appendages are the
chelicerae (modified for feeding), the second ones are pedipalps, usually modified
for feeding or for sensory functions. Excretory organs are coxal glands or
Malpighian tubules; the genital opening is on the 2nd opisthosomal segment.
Compare the horseshoe crab, scorpion, spider and other chelicerates, can you find
the unifying characters?
Phylum Arthropoda, Subphylum Chelicerata, Class Merostomata
These chelicerates have a high dorsal shield covering the prosoma and have 5 or 6
abdominal gills. The only living representatives are the Subclass Xiphosura and are
found on the east coast of the U.S., in the Gulf of Mexico, and the W. Pacific (Japan
& the Philippines). They are “living fossils” and have survived (as a taxon) for 400
million years (since the Ordovician Period).
2.
We have specimens of Limulus, the "horseshoe crab" for you to examine. The
body sections are the prosoma, the opisthosoma and the telson (or tail spike).
Note the Chelicera that give this subphylum its name.
Limulus – the “horseshoe crab”
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Phylum Arthropoda, Subphylum Chelicerata, Class Pycnogonida
The “sea spiders,” a group that is strictly
marine, tend to be small (about 10 mm),
although the largest is 75 cm they live on
hydroids, and suck in the tentacles and/or
the polyps while they cling to the hydroid
colony.
Nymphon – a pycnogonid “sea spider”
Phylum Arthropoda, Subphylum
Chelicerata, Class Arachnida
These are common, diverse, and primarily
terrestrial Arthropods. Arachnids are
characterized by two body regions (prosoma and opisthosoma), 4 pairs of walking
legs (as in merostomates), a highly modified opisthosoma, respiration by book lungs
and/or tracheae, and mouthparts modified for prey capture.
3.
Scorpion. The body is more obviously segmented than that of Limulus or
spiders. There is a cephalothorax (prosoma) and abdomen. There is a pair of
median eyes and several lateral eyes on each anterior lateral margin. Below
the anterior margin are the chelicerae, and to the side are the large pincers, the
pedipalps. Behind the pedipalps there are four pairs of walking legs. On the
venter of the abdomen are the spiracles, the openings of the book-lungs. The
end of the abdomen bears the telson, which is modified into a stinging barb.
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4.
Spider. Notice that the body is divided into a cephalothorax and an
unsegmented abdomen connected by a stalk, the pedicel. There are usually 8
simple eyes. How do the chelicerae and pedipalps differ from those of
scorpions? The chelicerae contain poison glands. The mouth opens between
the bases of the pedipalps. In the center and an opening on each side to the
book lung. At the posterior are found the spinnerets, which extrude silk.
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Phylum Arthropoda, Subphylum Mandibulata
These are mostly terrestrial arthropods, all with mandibular mouthparts, and both
uniramous (unbranched) as well as biramous (branched) appendages. The
mandibulate arthropods have opposing mandibles that either crush or bite with the
tip (compare with the chelicerae and gnathobases of Limulus, and the mouthparts of
spiders and scorpions).
EXERCISES:
Phylum Arthropoda, Subphylum Mandibulata, Class Myriapoda
Two of the major mandibulate taxa have many legs, and are called myriapods:
Order Chilopoda – the centipedes (hunters)
1. Examine a preserved specimen of a centipede. Can you find the antennae or
eyes? Turn the animal on its venter and notice the poison fangs (or
maxillipeds) and the serially homologous body, bearing one pair of legs on
each section. The last pair of legs is modified and can be used for grasping
prey. On the sides between the legs are spiracles.
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Order Diplopoda – Millipedes (vegetarians)
2. Examine a large millipede. Observe the head with simple eyes (not always
present) and antennae. The first section is covered by a large tergite (forming
a hood) called the collum. Each of the first body rings has one pair of limbs,
but in some groups their positions have shifted so that some rings have two.
Subsequent rings have two pairs of legs.
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Phylum Arthropoda, Subphylum Mandibulata, Class Insecta - The insects
The insects are characterized as mandibulate arthropods with three body regions:
head, thorax, and abdomen. The thorax bears three pairs of walking legs and wings
when they are present. Not all insects have wings; some groups lack them
altogether, while others have “lost” them secondarily during evolution.
3.
As a representative insect, we will use the large lubber grasshopper, Romalea,
for anatomy.
a. External Anatomy
The body of the grasshopper is divided into a head consisting of six fused
segments (somites); a thorax of three somites to which are attached the
legs and wings; had a long segmented abdomen that terminates with the
reproductive organs. The exoskeleton consists largely of chitin, which is
secreted by the epidermis. As they grow, grasshoppers periodically shed
the exoskeleton (molting or ecdysis) as do all arthropods; adults do not molt.
The head has one pair of slender, jointed antennae, two compound eyes,
and three simple eyes or ocelli. The mouth parts are of the chewing type
and include a broad upper lip or labrum; a tonguelike hypopharynx; two
heavy, dark, lateral jaws or mandibles, each with teeth along the inner
lateral margin for chewing food; a pair of maxillae of several parts, including
palps (sensory appendages) at the side; and a broad lower lip or labium,
with two short palps.
The thorax consists of three parts: a large anterior prothorax, the
mesothorax, and the posterior metathorax. Each part bears a pair of jointed
legs. Identify the leg segments indicated in the figure. The meso-and
metathorax each bear a pair of wings. The anterior wings of the
grasshopper are thick and shield the larger pair of flight wings. Both pair of
wings are derived from the cuticle and have thick parts (veins) that
strengthen them. Stretch out the wings and examine the anterior protective
wings and the flight wings.
The abdomen consists of eleven somites, the posterior ones being modified
for reproduction. The male has a blunt terminal segment, whereas the
female has four sharp conical prongs, the ovipositors, which are used in egg
laying. Along the lower sides of the thorax and abdomen are ten pairs of
spiracles, the small openings of air tubes (tracheae) that branch to all parts
of the body and constitute the respiratory system of the grasshopper. This
system of air tubes brings atmospheric oxygen directly to the cells of the
body. The spiracles open and close to regulate the flow of air.
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60
c.
Insect Metamorphosis - Examine the insect life cycle demonstrations.
Most insects undergo a definite series of changes during their development
(metamorphosis). In those without metamorphosis (ametabolous
development), the eggs hatch into young that, except for size, resemble the
adults (e.g., silverfish and springtails).
In those having hemimetabolous development, the eggs hatch into nymphs
(an immature stage) that generally resemble the adults except for being
adapted to aquatic life. The nymphs lack wings and may have external gills.
They undergo a series of molts and gradually develop into the adult form
(e.g., mayflies, dragonflies, stoneflies).
In those having gradual metamorphosis (paurometabolous development),
the wings develop as the insects mature. Except for the size and
rudimentary condition of the
genital appendages, the young
(also called nymphs) resemble
the adults. Transformation into
an adult occurs by means of a
series of molts during which the
wings develop and the
proportion of the body to the
head becomes that of the adult.
Furthermore, the young and the
adults occupy the same habitat
and feed on the same food
(e.g., grasshopper).
In those insects having complete metamorphosis (holometabolous
development), the young and adults are totally different in appearance. For
example, caterpillars develop into moths or butterflies, maggots become
flies, and grubs transform into beetles. The young insect, known as the
larva, occupies an entirely different habitat and has different food
requirements from those of the adult. When the larva has reached maturity,
it ceases to feed, settles down in one place, forms a pupa within which it
undergoes a series of morphogenetic changes, and emerges as an entirely
new form, the adult.
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Although the Class Insecta is comprised of >25 different orders (and nearly 1000
families!), the four orders described below represent the most common and familiar.
Look for representatives of these four orders (as well as all listed in list at beginning
of the Arthropod section) on demonstration.
Order Coleoptera – the beetles
Beetles constitute the single largest order of insects (and animals) representing
about 300,000 species or nearly one third of all known animal species. They are
recognized most easily by their hard bodies and chewing mouthparts. Adults usually
have two pair of wings, the front pair being modified as a hard protective covering
(elytra).
Order Lepidoptera – moths and butterflies
These insects include the familiar moths and butterflies. They have conspicuous
scaled wings and mouthparts modified into a long coiled proboscis specialized for
sucking flower nectar.
Order Diptera – the flies
Literally, Diptera means “two wings.” These are the true flies, Drosophila
melanogaster likely being the most familiar to scientists. All have functional front
wings, but the back wings are reduced and knoblike. These back wings (halteres)
aid in turning in flight. The group also includes mosquitoes, gnats, midges,
horseflies, and other summer nuisances.
Order Hymenoptera – wasps and ants
Bees, wasps, sawflies, and ants comprise this large order. All have chewing
mouthparts. It is among the hymenopterans that social behavior in animals has
reached its highest development. Many species are eusocial with distinct division of
labor and reproduction within colonies.
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Phylum Arthropoda, Subphylum Mandibulata, Class Crustacea
This is the only large group of arthropods that is nearly entirely aquatic.
Appendages in the Crustacea are biramous - they have two parts. There are 5 pairs
of head appendages: antennules, antennae, mandibles, and 2 pairs of maxillae.
The number of trunk appendages varies greatly. There are 10 subclasses in this
subphylum, although not all are equally common, or equally represented in this lab
exercise. We will cover a variety of taxa comprising the most common crustaceans.
The taxonomic organization of the Crustacea is complex, and changing (even as we
speak!).
Phylum Arthropoda, Subphylum Mandibulata, Class Crustacea,
Subclass Malacostraca
This Subclass contains 75% of all the crustaceans and includes all the larger
representatives. They are united by the following features: head with 5
appendages, may have a carapace, thorax with 8 pairs of thoracopods, abdomen
with 6 segments with or without pleopods, and a terminal telson.
Order Stomatopoda - mantis shrimp. The second pair of thoracic appendages
are large, and resemble the fore-legs of the “praying mantis”, hence the name.
These are used in prey capture, and in territorial defense.
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Order Isopoda - found in marine, freshwater and terrestrial systems. They are
flattened dorsoventrally. They have 6 pairs of uniramous thoracopods. The
pleopods function in gas exchange. The only terrestrial crustaceans, pillbugs, are
members of this order. We may have live specimens of freshwater and terrestrial
isopods for you to examine.
Order Amphipoda - “scuds” or side swimmers. In contrast to the isopods these
tend to be laterally flattened. Like the isopods they lack a carapace and have
uniramous thoracopods. We may have live amphipods for you to examine.
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Order Decapoda - These are the familiar shrimp, lobsters and crabs. We will
have a large number of specimens on demonstration. The first three thoracopods
are modified as maxillipeds, leaving 5 pair of unmodified legs (thus the name deca,
or 10). The gills are thoracic and are always enclosed by the carapace. The first
walking legs are chelate, having a pair of claws (which are often enlarged).
The shrimp. The body is laterally compressed. The pleopods are well adapted
for swimming and the thoracopods are very slender.
The creeping decapods. The abdomen is reduced, and they usually have an
enlarged cheliped. Lobsters and crayfish have conspicuous uropods and large
abdomen. True crabs have an abdomen that is greatly reduced and flexed under.
Hermit crabs and mole crabs have a reduced abdomen (it may also be soft and
vulnerable, e.g., as in hermit crabs, which use abandoned gastropod shells as
protection).
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EXERCISES:
1.
Cambarus, the freshwater crayfish (or “crawdad”) will serve as a representative
decapod crustacean for anatomy.
a. External Anatomy
The 5 head segments and 8 thoracic segments are fused to form the
cephalothorax, covered dorsally by the hard carapace. Dorsally on the
carapace you can find the anterior projection between the compound eyes,
the rostrum.
On each side of the rostrum are the stalked compound eyes. Anterior are
the antennules (1st antennae) and the antennae (2nd antennae). There are
6 pairs of mouth appendages (see b. below). The chelipeds are the largest
limbs, each with a large claw. Are the claws on each side exactly alike?
The cheliped on each side is followed by 4 pairs of walking legs, pereopods.
The abdomen has 6 pairs of pleopods (swimmerets). In the male the first 2
pairs are modified. What is the sex of your specimen? The last abdominal
somite bears the uropods, which are enlarged for swimming.
Examine a cheliped and compare it to a walking leg and determine what
parts form the chela or claw. Are the walking legs and chelipeds biramous
appendages (like the pleopods) or uniramous?
The abdomen has 6 movable somites, each bearing a pair of jointed
appendages, and the telson (which lacks appendages but has the anus on
its venter). Each somite has a tergum (dorsal plate) with a pleuron (lateral
extension) and a sternum (ventral plate).
b. Mouthparts
Put the crayfish on the dissecting pan, venter up, and find the mouth
appendages. Use a blunt probe to move them about. Note how the
appendages are associated with each other.
The outer mouthpart appendages are the first maxilla (You may want to
remove the mouthparts, but keep them in order), the second maxilla and 3
pairs of maxillipeds. Beneath these are the mandibles, almost completely
covered by the outer appendages. Are the teeth on the left and right
mandible exactly alike?
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67
THE MICROCRUSTACEANS
These groups are important in freshwater and marine ecosystems as zooplankton the base of food chains. They are small in size, and have been studied extensively
in the field as well as in laboratory research on physiology and behavior.
Phylum Arthropoda, Subphylum Mandibulata, Class Crustacea,
Subclass Branchiopoda
This group is united by having trunk appendages that are flattened and leaflike,
hence the name “gill feet”. We have two representative types of branchiopods,
which you can examine as living specimens.
Order Anostraca - the brine shrimp or fairy shrimp
These microcrustaceans hatch from eggs and live their lives very quickly in
temporary ponds and tidepools. We will have a culture of brine shrimp. You
should be able to find the larval stages typical of most crustaceans, the nauplius
larvae, as well as developing and adult brine shrimp.
Nauplius Larva
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Order Cladocera - water fleas
These are represented by the “classic” microcrustacean, Daphnia. We may have a
culture of living Daphnia as well as prepared slides for you to examine. Place the
live specimen in a concavity slide and observe its swimming behavior. You should
be able to get one on its side “sandwiched” under a cover slip for more high power
observation. If that doesn’t work, use a slowing agent. Visible through the
transparent carapace of Daphnia are its beating heart, its digestive system, ovary,
brood pouch, and thoracic appendages. You should also locate the antennae and
eyes.
Phylum Arthropoda, Subphylum Mandibulata, Class Crustacea,
Subclass Ostracoda - the “seed shrimp”
These tend to be very small, benthic dwellers. The body is enclosed in a bivalved
carapace. They have few thoracic appendages (0, 1 or 2 pairs), but have long 1st
antennae and a posterior caudal ramus which they use for locomotion. We may
have live specimens for you to observe.
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Phylum Arthropoda, Subphylum Mandibulata, Class Crustacea,
Subclass Copepoda
These have a cylindrical body, median eye and long antennae. They are both
marine and freshwater and may be parasitic. These planktonic microcrustaceans
swim using their second antennae (antennules).
We have living Cyclops, so named because of the single median eyespot. Examine
a specimen in a drop of water on a concavity slide, first under the dissecting scope,
and then under the compound scope.
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Phylum Arthropoda, Subphylum Mandibulata, Class Crustacea,
Subclass Cirripedia
These are the barnacles, which have “feathery feet”, hence the name. They attach
on a substrate (often on ships or docks) on their anterior end “upside down”, with
their thoracic appendages reaching out of skeletal plates to filter the water for food.
We will have several preserved specimens and barnacle “shells” on demonstration.
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MOLLUSCS
TAXONOMY:
Phylum Mollusca
Class Polyplacophora
Class Scaphopoda
Class Bivalvia
Class Gastropoda**
Sub-Class Eogastropoda - Limpets
Sub-Class Orthogastropoda – Snails & Slugs
Class Cephalopoda
The phylum Mollusca is among the most conspicuous of the invertebrate phyla. They
have been collected, eaten, and coveted since humans emerged. A collector of shells
is considered a conchologist, whereas those who study the Mollusca are malacologists.
There is no apparent metamerism (segmentation) in these soft bodied animals, and the
body form is frequently secondarily modified to an asymmetrical condition. The shell,
when present, is secreted by the mantle, a flap of tissue covering the dorsal surface.
LABORATORY OBJECTIVES:
Through this laboratory exercise, you should:
1. Learn to recognize the mollusc subclasses and be familiar with their external
anatomy.
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EXERCISES:
Phylum Mollusca, Class Polyplacophora
Several types of chitons will be on exhibit. Examine the external anatomy of a
preserved specimen, or look at a live one (if available).
1.
On the dorsal surface note the 8 calcareous plates which overlap each other and
the girdle which binds them together. Turning the animal over, observe: a) the
mantle which covers the visceral mass dorsally and produces the girdle and shell
plates; b) the mantle groove or cavity extending along the sides of the large flat
muscular foot; c) the small inconspicuous head with a slit-like mouth and lacking
sensory organs; d) the ctenidia or gills in the mantle cavity. These may be
restricted to the posterior half of the groove or extend nearly to the head depending
on the species; e) posterior anus.
Dorsal
Surface
Ventral
Surface
Calcareous
plates
Girdle
(mantle)
Phylum Mollusca, Class Scaphopoda
The tusk shells are burrowing mollusks that have
extremely modified body parts. The shell is shaped
like a tusk with both ends open and grows linearly.
The water current enters and exits through the top
hole while the foot extends
out the bottom hole and is
used in burrowing. We have
some tiny preserved
specimens for you to look at
on demonstration. Unlike
other molluscs, scaphopods
do not have ctenidia, a heart
or a circulatory system.
Circulation of blood
throughout the hemocoel
results from rhythmic
movement of the foot.
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Phylum Mollusca, Class Bivalvia
The bivalves are laterally compressed molluscs whose shell consists of two dorsally
hinged valves. The head and radula are absent and they have a simplified nervous
system. The mantle cavity is the largest of any mollusc and includes the enlarged gills
which serve as both respiratory organs and as food gatherers.
1.
Demonstrations and live material: if available, live material in the lab will show the
adaptive radiation of this group. If we have "Coquina" clams, see how quickly they
burrow. Other types of bivalves, including edible clams, oysters, and scallops, will
be on demonstration. The “shipworms” are actually bivalves able to penetrate
wood and are pests of pilings and other man-made structures.
LIVER
(Green
digestive
gland)
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Phylum Mollusca, Class Gastropoda
Gastropods are quite diverse in form and vary considerably in size. Currently the
taxonomy of this group is undergoing significant revision. Not all gastropods have
shells (e.g., nudibranchs have secondarily lost their shells). Bodies are generally
asymmetrical, and frequently exhibit torsion. The head has tentacles and eyes and the
ventral foot is well developed for locomotion. A radula with rows of teeth is used for
feeding.
2.
We will have representatives of the two
gastropod subclasses (Eogastropoda
and Orthogastropoda) on
demonstration. Take time to examine a
variety of specimens. On the basis of
this cursory examination, contrast the
three major groups of snails. How do
they differ in modes of respiration? How
does torsion differ from coiling?
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Phylum Mollusca, Class Gastropoda, Subclass Orthogastropoda – Marine Snails
The gills are contained within the mantle cavity and can be one or two in number.
These exhibit the most primitive type of gill structure and water circulation. Shells of
prosobranchs may be flat or spirally coiled. Most have an operculum. Observe the
variation in shell form, the foot and its movement, the tentacles and eyes. Living
specimens of several species may be on display if available.
Phylum Mollusca, Class Gastropoda, Subclass Orthogastropoda- sea slugs
These gastropods have one gill, one auricle and one nephridium but display a
secondary loss of torsion. Generally there is a reduction or loss of the shell and mantle
cavity. There is a secondary bilateral symmetry. The head has tentacles. They are
hermaphroditic, and all are marine. There are two orders that have been well-studied in
marine biology and neurobiology: Order Aplysiacea - the seahares, and Order
Nudibranchia - sea slugs. Of the Aplysiacea, Aplysia is used extensively in
neurobiology and behavior research because of its simple nervous system.
Nudibranchia is a large and very colorful group of molluscs, and different species may
be either herbivorous or carnivorous. The dorsal side of the organism is covered with
spikes, plumes, or balloons called cerrata, and some species have feathery gills at the
dorsal end.
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Phylum Mollusca, Class Gastropoda, Sub-Class Orthogastropoda- Land/Fresh water
snails and slugs.
In members of this group the mantle cavity is converted into a vascular chamber for gas
exchange in air or in water which lacks a ctendium but may contain gills. They are
hermaphroditic. A shell is present, but there is no operculum. In slugs this shell is often
not readily visible because it is contained within the mantle. The pulmonate snails may
be divided into three orders on the basis of their tentacles and presence/absence and
shape of the shell. The Eupulmonato (largely fresh-water snails) generally have a
single pair of tentacles with eyes at the base and have spiral shells that may be internal
or externally housed. The Stylommatophora, (land snails), have 2 pairs of tentacles
with eyes at the tip of the posterior pair. The Systellomatophora have 2 pairs of
tentacles with eyes located at the base of the upper tentacles and most members of this
order lack a shell entirely. Examples of these orders will be on display.
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Phylum Mollusca, Class Cephalopoda
These are the largest, fastest and “smartest” invertebrates. Despite these
achievements and their bizarre form, they nevertheless exhibit all the basic molluscan
features. The shell is reduced in many groups, the foot is variously modified as a
siphon and tentacles, the circulatory system is closed and there is extensive
cephalization.
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FEMALE
VENTRAL SIDE
MALE
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DORSAL SIDE
LABS 13 and 14: ECHINODERMATA
TAXONOMY:
Phylum Echinodermata
Sub-Phylum Asterozoa
Class Stelleroidea
Sub-Class Asteroidea
Sub-Class Ophiuroidea
Sub-Phylum Echinozoa
Class Echinoidea
Class Holothuroidea
Sub-Phylum Crinozoa
Class Crinoidea
The name of this phylum is derived from one of its distinguishing characteristics - “spiny
skin”. The phylum is named because of the spiny plates (composed of calcareous
ossicles) that form an internal skeleton just below the surface of the skin. These are
familiar marine animals known as starfish, sea urchins, sand dollars, etc.
Echinoderms are known for their pentaradial symmetry, which means that the body
symmetry is based on multiples of 5. They are coelomate, but in contrast to the
protostomate phyla (whose coelom develops from a split in the mesoderm), the
echinoderms develop a coelom as outpocketings of the embryonic mesoderm of the
gut. The echinoderms are referred to as “deuterostomate” because during
development, the mouth forms as the second opening in the embryo (the anus is first).
Because of their “ass-backwards” embryogenesis, echinoderms are considered more
closely related to chordates (including vertebrates) than to other invertebrate phyla.
Another characteristic of the echinoderms is the water vascular system, which is derived
from the coelom, and functions primarily in locomotion and food acquisition.
LABORATORY OBJECTIVES:
Through these laboratory exercises you should:
1. Be able to identify the classes and subclasses of the Echinodermata.
2. Become familiar with the external anatomy of each group
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EXERCISES:
Phylum Echinodermata, Class Stelleroidea, Subclass Asteroidea - (sea stars - includes
most common starfish)
Starfishes have large radially arrayed arms into which the body cavity, WVS and large
caeca of the gut extend. In these animals the mouth is turned downwards. The most
primitive starfishes have a blind gut with no anus; however, in the majority of present
day starfishes an anus has developed on the upper surface. The gonads lie inside the
arms, and open to the exterior by way of definite gonoducts and gonopores. The larval
stage resembles that of a sea cucumber, and is called by the same name (auricularia),
but many starfishes have acquired a second or third larval stage which develops after
the auricularia stage. Starfish are predators, and are found all over the ocean, and
descend into the greatest depths. Modern starfish include many forms which so closely
resemble Paleozoic forms that it is now thought very likely that most of the existing
groups had already differentiated before the onset of Mesozoic times.
1.
Live specimens: we may have a number of living asteroids on demonstration. Be
sure to see them, and observe the mechanics of the tube feet.
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b.
RECTUM
(PYLORIC CAECUM)
(PYLORIC CAECUM)
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Phylum Echinodermata, Class Stelleroidea, Subclass Ophiuroidea – the brittle-stars
Ophiuroids differ from starfishes in having slender arms which are capable of rapid
lashing movements, in having no ambulacral groove and having paired bursae, i.e.,
reproductive chambers, on the lower surface of the disk. Primitive ophiuroids resemble
starfishes more closely, having, for example, extensions of the coelom, gut, and
reproductive organs in the arms (features formerly supposed to distinguish ophiuroids
from starfishes). The larval stage, if present, is a vitellaria larva in the cases of the more
primitive groups, that is to say, in groups which seem to resemble most closely the
Paleozoic ophiuroids, or a pluteus larva, resembling that of sea urchins. The internal
anatomy of ophiuroids resembles in major features that of starfishes, though the
alimentary system is much simpler, and the gut is always blind.
Locomotion depends upon arm motions, unlike starfishes, where the tube-feet are the
active locomotor organs. There are no pedicellariae in ophiuroids. Ophiuroids are
among the most abundant animals on the planet, as sea-floor photography has
disclosed enormous populations carpeting the abyssal muds at intervals of 12 inches or
so.
3.
We will have a number of brittle stars; be sure to see them and handle them if you
like.
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Phylum Echinodermata, Class Echinoidea - sea urchins, sand dollars
Irregular Urchins - Include the Sea Biscuits, Sea Cakes, Heart Urchins and Sand
Dollars. Their anus is located on the oral surface. There is a more marked tendency
toward bilateral rather than biradial symmetry in some forms. These are basically
detritivores that live in sandy substrate and strain food from the bottom ooze.
Regular Urchins - The most familiar form of echinoderms, the Sea Urchins, are “regular”
in shape. They have prominent spines, an aboral anus, a food gathering device oddly
called Aristotle’s Lantern, and a penchant for eating anything that will hold still long
enough. The pentaradial symmetry is less conspicuous in the Echinoids, but if you
examine the dried tests of specimens, the arrangement will be quite easily seen. We
will have a number of echinoids on demonstration. Be sure to see them.
1.
We will use Strongylocentrotus, a common sea urchin, as an example. Examine a
live or preserved specimen of these “purple sea urchins.”
a. External Anatomy
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Most sea urchins live on the
sea-floor with the oral surface
turned downwards, the anus
directed upwards, and can
move in any direction.
Therefore we cannot properly
speak of anterior or posterior,
though it is evident that the
down-turned oral surface
corresponds to the anterior
end. Some sea urchins have
acquired a bilateral symmetry,
and these have the oral
surface placed anteriorly.
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Phylum Echinodermata, Class Holothuroidea - sea cucumbers
This class generally has an elongate oral/aboral axis with mouth and anus at opposite
ends of the poles. The respiratory tree or tentacles are used primarily for feeding, while
the anus is often a respiratory device. When disturbed, cukes have a penchant for
eviscerating which can be quite traumatic to a predator. The cuke normally survives
though regeneration time may be quite extensive depending upon species and relative
health of the animal at the time of evisceration.
These echinoderms show a number of anatomical features which are also found in
some of the most ancient Paleozoic echinoderms. Although it is still uncertain whether
the resemblances are due to convergence, or due to a real genetic relationship, the sea
cucumbers do at least offer us an opportunity to study the kind of body structure which
seems to have characterized the early members of the Echinodermata.
2.
We will have some preserved sea cucumbers, and this exercise will involve
examination of Cucumaria.
a. External Anatomy
MOUTH
INTEGUMENT
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Phylum Echinodermata, Class Crinoidea - sea lilies and feather stars
Crinoids are the only surviving members of the subphylum Crinozoa, which in Paleozoic
times comprised an immense assemblage of varied echinoderms. All characterized by
a central cup-shaped body from which rises a crown of feather-shaped arms; the mouth
is directed upwards, and the gut is U-shaped, so that both the mouth and anus lie on
the upper surface of the body.
So far as is known, all crinoids develop a stem, by which they are attached to the seafloor or other substate; but in the case of feather stars, the stem is discarded in the adult
stage, to be replaced by a ring of attachment structures called cirri. Crinoids are
suspension feeders, and capture zooplankton and other food with tiny tentacles on the
feathery arms.
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LARVAL STAGES OF ECHINODERMS
The development of echinoderms has been studied extensively, and they are used as a
standard demonstration in developmental biology classes. They are deuterostomes (a
major evolutionary branch of the animal kingdom, which includes the chordates). The
sea urchin Arbacia is a classic model. We have slides of their development for you to
look at.
Once the embryo reaches the gastrula stage, it develops into a larval form characteristic
of each class. We will have these on demonstration or as slides for you to examine.
The larval forms of all echinoderms first exhibit bilateral symmetry, then develop into the
pentaradial symmetry characteristic of the phylum. The sea stars (Asteroidea) for
example, have two stages: the
bipinnaria, which is a bilaterally
symmetrical planktonic form
with ciliated locomotory bands,
followed by the brachiolaria, in
which the arms can be seen.
Sea urchin larvae (Echinoidea)
resemble those of sea
cucumbers (Holothuroidea),
and are called by the same
name - auricularia. Echinoids,
however, then develop into an
echinopluteus larval form.
Brittle stars (Ophiuroidea) are
similar, but have ophiopluteus
larvae. The larvae of crinoids
are called doliolaria larvae.
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