Invertebrate Tutorial
and Notes
Phylum Porifera (Sponges)
- There are no true tissue layers
- Sponges consist of hollow body cavity that water circulates
through
- They are filter feeders, in which they absorb nutrients from the
water
types of sponges
- habitat: mostly marine (aquatic environment)
circulation of water
through out the sponge
Sponges are made of different types of cells. The collar cells have
a flagella that circulate the water through out the sponge and absorb
nutrients. Some of the mesophyll cells of the sponge contain
spicules, which are tiny, needle like structures. Sponges also
contain amoebocytes that digest the food particles the collar cells
absorb from the water.
Phylum Cnidaria
(Jellyfish, Hydra, Sea Anemone & Corals)
Cnidarians have tentacles that contain cnidocytes, which are
stinging cells that enable the cnidaria to kill or paralyze its
prey. The cnidocytes contain nematocysts, which is the
thread and barb of the cnidocyte cell. The barb attaches to
the prey and the thread stings the prey.
1. mouth
3. tentacle
Hydra:
Has a polyp shape, mouth
on the dorsal surface &
tentacles point upward
Cnidarians have a gastric cavity in which food is broken
down and waste is released- they do not have a digestive
tract.
2. gastric
cavity
3. tentacle
1. mouth
Cnidocyte cells
with nematocysts
(barb & thread)
Jellyfish:
Has a medusa shape,
mouth on the ventral
surface & tentacles point
downward
Phylum Platyhelminthes
(Flatworms)
Flatworms can be free-living or parasitic and they have bilateral
symmetry.
Planarians are aquatic flatworms that feed on dead organic matter.
Planarians are hermaphrodites and reproduce sexually. They can
also reproduce asexually through fragmentation. They have a
primitive digestive system, eyespots that sense only light- not
distinct shapes or images and a simple nervous system with
ganglia.
Tapeworms and flukes are parasitic flatworms that feed off of
human beings. Both types of worms infect the intestines of the
host and feed off the host’s tissue and the digested food of the host.
Tapeworms have a head called a scolex that contains a knobshaped head with hooks and suckers with which they attach to its
host. They also contain proglottids which are segments of the
tapeworm that contain male & female anatomy and fertilized eggs.
One proglottid can contain 10,000 eggs.
scolex of a
tapeworm
tapeworm
planarian: nonparasitic flatworm
1. ventral
feeding tube
2. digestive
system
3. anterior
brain
4. anterior
eyespots
Phylum Nematoda
(Roundworms)
Roundworms can be free-living or parasitic. They contain a
one way digestive tract with a mouth and anus. They are
pseudocoleomates in which they have a partial coelom.
Many roundworms are human parasites, such as Ascaris,
pinworms and Trichinella. Ascaris infects the human
digestive system and can block the small intestines.
Pinworms infect the intestines and cause anal itching when
they lay eggs around the anus. Trichinella is a roundworm
that can be contracted by eating undercooked pork.
Trichinella
Ascaris
Pinworm
Phylum Annelida
(Segmented worms)
anus
Segmented worms can be free-living or parasitic. They
contain a one way digestive tract with a mouth and anus.
They are coeleomates in which they have a fully lined
coelom that contains organs. Annelids are found in both
terrestrial and aquatic environments. Examples of annelids
are earthworms and leeches.
They contain a hydrostatic skeleton which provides
support to the annelid, much like how water provides
support to a water balloon. They also contain
nephridia, which are tubes that the annelid uses
to excrete liquid waste.
Earthworms are hermaphrodites,
in which they contain both male and
female anatomy. They can
not fertilize themselves and must
swap gametes with another
earthworm.
clitellum
brain
intestine
mouth
esophagus
Leeches are parasites that are found in freshwater. They feed
off the blood of their hosts.
leech
ventral nerve cord
Phylum Mollusca
Class Gastropoda
Gastropods are part of the phylum Mollusca. The majority
of mollusks contain a mantle, which is the soft outer layer of
their bodies the secretes the shell. They also contain a
visceral mass, which is the internal organs of the mollusk.
Mollusks have a soft body and most mollusks have a shelleither external or internal. The muscle of the mollusks is
called the foot and is used for movement.
1. spiral shell
4. eye stalks
Gastropods are mollusks with a one-piece shell or no shell at
all and have bilateral symmetry. Examples are snails, conchs
and slugs.
Gastropods contain a radula, which is a tongue like organ
that protrudes from the mouth and is used to scrape up algae
or tear apart leaves. They also contain eye stalks that sense
light and some movement.
3. mouth with
radula
2. muscular foot
makes slime
They move using their muscular foot which produces slime
and enables them to glide more easily across their terrain.
slug
conch
Phylum Mollusca
Class Bivalvia
Bivalves are organisms with two shells that are attached by a hinge. Examples are clams, oysters, mussels and
scallops.
Bivalves do not have bilateral symmetry like gastropods and they do not contain a radula. Instead, bivalves are
filter feeders and are found only in aquatic environments. They use their gills to obtain oxygen for breathing and
to trap food particles from the water.
Certain bivalves, such as oysters, have the ability to make pearls. Pearl formation begins when a foreign object,
such as a grain of sand, lodges between the mantle
and the shell. The mantle secretes
shell like material around the
1.
stomach
grain of sand and forms a
pearl.
2.
mouth
7.
3.
mussels
gills
muscular foot
4.
brain
5.
intestine
6. mantle
secretes shell
Phylum Mollusca
Class Cephalopoda
Cephalopods are tentacled mollusks with either an internal or external shell. Examples are squid, octopus and
nautilus.
Cephalopods have a highly developed nervous system that allows them to have quick responses and to be agile
predators. Cephalopods have the most advanced eyes that can detect color, movement and shades of light and
dark.
The squid has an internal shell and skin with chromatophores.
Chromatophores enable the squid to change its skin color to blend into
the environment. Squid and octopus have a strong beak sued to eat their
pry and ink sacs. The ink is squeezed out of the ink sac and used as a
smoke screen when the cephalopods are threatened by a predator.
nautilus: contains a spiral
shell with tentacles
2. mantle
1.
beaked mouth
3. fins
4. skin with
chromatophores
5. 8 arms
2 tentacles
Phylum Arthropoda
Class Crustacea
Arthropods are segmented invertebrates with joined appendages and an exoskeleton. The appendages are body
extensions that are used for movement, obtaining food, reproduction and sensing the environment. The
exoskeleton is a hard outer covering made of chitin that is used for support and protection. The exoskeleton
limits the size on an arthropod and it must shed its exoskeleton every time it grows through a process known as
molting.
Most crustaceans are aquatic and have a hard exoskeleton. Examples are shrimp, crayfish, lobster, crab,
barnacles and pill bugs.
Crustaceans usually have 10 appendages and the front legs are pinchers. They also contain mandibles that are
jaw like appendages used for chewing and crushing food. To aid in swimming, crustaceans have swimmerets
on their abdomen. Crustaceans like crayfish have
2 pairs of antennae.
1.
2 pr antennae
2. 1 pr feeding/defense legs
3.. 4 pr walking legs
4... muscular tail with ventral swimmerets
Crustaceans are primarily
aquatic but a few live on land.
For example, the pill bug
lives in damp areas under
leaves and dead wood.
Phylum Arthropoda
Class Arachnida
Arachnids are a type of terrestrial arthropods that have 8 legs and 2 body
segments known as a cephalothorax (the head and thorax fused together) and
an abdomen. The abdomen is large and swollen in appearance. Examples are
spiders, scorpions, ticks, dust mites, horseshoe crabs and chiggers.
Spiders are the only animals that have the ability to spin a web. They produce
silk from spinnerets at the end of the abdomen. Webs are used for hunting,
sensing and reproduction.
tick
Ticks are a type of parasite that suck their hosts blood. The abdomen swells and
become larger with the more blood the tick sucks.
mite
scorpion
spider
chigger
Phylum Arthropoda
Class Insecta
Insects are a type or aquatic and terrestrial arthropod that has 3 body segments, compound eyes and six legs. The 3
body parts are the head, thorax and abdomen. The head contains the brain and mouth parts. The thorax contains
the legs and wings and the abdomen contains the reproductive, respiratory and excretory systems. Examples are
bugs, flies, bees, termites and grasshoppers.
Many insects go through a metamorphosis, or a series of changes during which the larvae becomes an adult.
There are 2 types of metamorphosis: complete and incomplete. In incomplete metamorphosis, the larvae looks
like a smaller version of the adult and has in between stage of larvae and adult known as a nymph.
In complete metamorphosis,
compound eye
the larvae looks completely antennae
different than the adult. The
larvae goes through a pupal stage,
in which the larvae tissue breaks
head
down and the adult tissue
develops.
thorax
incomplete
metamorphosis
complete
metamorphosis
abdomen
Phylum Echinodermata
(Starfish, sea urchins, sand dollars and sea
cucumbers)
Echinoderms are spiny skinned
organisms that have radial symmetry and
a 5 part body plan. Echinoderms move by
using a water vascular system, which is
a network of water filled tubes.
Echinoderms also contain tube feet which
are part of the water vascular system and
act as suction cups to attch to surfaces and
pull prey, such as bivalves, apart.
Sea cucumbers, a type of echinoderm,
have the ability to shoot out long, thin
tubules from its anus when it is threatened
by a predator. The predator becomes
entangled and leaves the sea cucumber
alone. Certain species of sea cucumbers
will shoot out its whole digestive system
at the predator. It takes a couple of days
for the sea cucumber to regenerate its
digestive tract.
sea
cucumber
sea
urchin