Animals, Part 1
Invertebrates
ANIMAL KINGDOM
 Welcome to your Kingdom!
 Animal diversity extends far beyond humans, dogs,
cats, birds, and fish. There are up to 200 million
living species of animals in the world today. This
vast diversity encompasses a spectacular range of
variation, from corals to crocodiles. First, we will
consider the characteristics that all animals share as
well as those that make them different and divide
them into taxonomic groups.
Animals
 Animals are multicellular, heterotrophic eukaryotes
with tissues that develop from embryonic layers.
Animals differ from both plants and fungi in their mode
of nutrition. Plants are autotrophic (make their own
food) eukaryotes capable of generating energy through
photosynthesis. Fungi are heterotrophs (cannot make
their own food) that grow on or near their food, releasing
enzymes that digest food outside their bodies. Unlike
plants, animals cannot make their own energy so they
ingest food, either by eating other living organisms or by
eating nonliving organic material. But unlike fungi,
animals use enzymes to digest their food after they have
ingested it.
Protists
 Protists are prokaryotes. Plants, fungi, and animals are
eukaryotes. Plants, fungi, and animals are multicellular,
but animals do not have cell walls like plants and fungi.
Cell walls function for structural support. Since animals
do not have cell walls, their bodies are held together by
proteins, the most abundant being collagen. Collagen is
a protein that is secreted by animal cells and deposited
outside of the cell boundary, between other cells. The
area between cells is called the matrix. Thus, collagen
deposits are called an extracellular matrix. Animals have
two specialized types of cells that are not seen in any
other multicellular organism: muscle cells and nerve
cells. Therefore, animals are capable of movement and
impulse conduction.
Reproduction
 Protists usually reproduce by binary fission; they
simply duplicate themselves asexually and split in
two. Plants and fungi can often reproduce both
sexually and asexually. Animals usually reproduce
sexually. In most species, a small, flagellated sperm
cell fertilizes a larger, non-motile egg, forming a
zygote that contains genetic information from both
parents. The zygote then undergoes a succession of
mitotic cell divisions and develops with layers of
embryonic tissues that will develop into a fully
mature adult body.
Reproduction
 Some animals (like humans) develop directly into
adults through stages of maturation, but many
animals also include at least one larval stage. A
larva is a sexually immature form of an animal that
looks different from the adult stage, usually eats
different food, and may even have a completely
different habitat than the adult, as in the case of the
tadpole. Animal larvae eventually undergo
metamorphosis to transform into the adult animal.
Clades and Grades
 A clade is defined as a group of organisms
consisting of a single common ancestor and all the
descendants of that ancestor. Clades are further
subdivided by their general appearance. A group of
animal species that share the same level of
organizational complexity is known as a grade. For
instance, slugs and snails are in the same grade,
even though snails have shells and slugs do not.
Within a grade, organisms are further differentiated
according to their body plan.
BODY PLANS
 Animals can be categorized according to their symmetry
(or lack thereof). Most sponges, for example, lack
symmetry altogether. Among the animals that do have
symmetrical bodies, symmetry can take different forms.
Some animals exhibit radial symmetry, such as sea
anemones: any imaginary slice through the central axis
divides the animal into mirror images. Bilateral
symmetry is found in animals such as a lobster or
human, which have a mirror image only on the right half
and left half of the body, but the top and bottom are
different and the anterior (head) and the posterior (tail)
ends are different.
BODY PLANS
 Many animals with a bilaterally asymmetrical body plan (such as
arthropods and mammals) have sensory equipment concentrated
at the anterior end, along with a central nervous system (brain) in
the head. The symmetry of an animal generally fits its lifestyle.
Many animals with radial symmetry are sessile (live attached to
an object) or planktonic (drifting or weekly swimming, such as
jellyfish). Their symmetry allows them to meet the environment
equally well from all sides. In contrast, bilateral animals generally
move actively from place to place. Their central nervous system
enables them to coordinate complex movements involved in
crawling, burrowing, flying, or swimming.

 Those organisms that have bilateral symmetry are grouped into a
category called the Bilateria. They can be further divided into
invertebrates and vertebrates.
ANIMAL KINGDOM
A. PORIFERA (no symmetry; sponges)
B. CNIDARIA (radial symmetry; jellyfish)
C. BILATERIA (bilateral symmetry; all other animals)
1. INVERTEBRATES
a) PLATYHELMINTHES (flatworms)
b) NEMATODA (roundworms)
c) ANNALIDA (segmented worms)
d) MOLLUSCA (snails, clams, squid, octopus)
e) ARTHROPODA (spiders, insects, crabs)
f) ECHINODERMATA (starfish)
2. VERTEBRATES
INVERTEBRATES
 Most of the animals alive today are invertebrates.
Invertebrates account for 95% of known animal
species and all but one of the animal phyla listed
above. Invertebrates occupy almost every habitat
on earth, from scalding water released by deep-sea
hydrothermal events to the rocky, frozen ground of
Antarctica.
PORIFERA
 A. PORIFERA (no symmetry; sponges)
 Sponges are sessile and have a porous body and
choanocytes. The term “sessile” refers to it being
anchored in one spot. Animals that are “sedentary”
are those that do not move much. Sponges are so
sedentary that they were mistaken for plants by the
ancient Greeks.
 Sponges have complex tissues. They lack a
digestive tract, lack body symmetry, and have no
nerves or muscles.
PORIFERA
 Living in both fresh and marine (salt) water, sponges are
suspension feeders: they capture food particles
suspended in the water that pass through their body.
Their body resembles a sac perforated with pores. Water
is drawn through the pores into a central cavity, and
then flows out of the sponge through a larger opening.
Sponges lack true tissues, but the sponge body does
contain several different cell types. Lining the interior of
the central cavity are flagellated choanocytes, or collar
cells. A choanocyte is a flagellated cell which sweeps
water through a sponge’s body. The flagella move back
and forth, generating a water current, and the collars
trap food particles that the choanocytes then ingest by
phagocytosis.
PORIFERA
 Most sponges are hermaphrodites (named for the Greek
god Hermes and goddess Aphrodite), meaning that each
individual has both male and female sexual reproductive
organs. Almost all sponges exhibit their
hermaphroditism in sequence, functioning first as one
sex and then as the other. Gametes (either an egg or a
sperm) arise from the choanocytes. The eggs stay within
the sponge, but the sperm are carried out of the sponge
by the water current. Cross-fertilization results from
some of the sperm being drawn into neighboring
individuals. Fertilization occurs within the sponge,
where the zygotes develop into flagellated, swimming
larva and disburse from the parent sponge. Upon
settling on a suitable substrate, a larva develops into the
sessile adult.
PORIFERA
 Sponges produce a variety of antibiotics and other
compounds that researchers can use to fight human
diseases. For example, one compound in marine
sponges can kill penicillin-resistant strains of the
bacterium Streptococcus. Other research is being done to
find anti-cancer agents from sponges. Also, sponges are
made of glass-like fibers that are one of the strongest
glasses known to man. By studying the glass sponge,
scientists could learn how to create unbreakable glass. It
may also hold the secret to making glass at room
temperature, instead of the extremely high temperatures
required to do so today.
CNIDARIA
 B. CNIDARIA (radial symmetry; jellyfish)
 Cnidarians have radial symmetry, a gastrovascular
cavity, and cnidocytes. This is one of the oldest
animal groups, and they have diversified into a
wide range of both sessile and floating forms,
including jellyfish, corals, and hydras. The basic
body plan of a cnidarian is a sac with a central
digestive compartment called the gastrovascular
cavity. A single opening to this cavity functions as
both mouth and anus.
CNIDARIA
 There are two variations on this body plan: the sessile
polyp and the floating medusa. Polyps are cylindershaped organisms that adhere to a substrate (like a rock)
and extend their tentacles, waiting for prey. Examples of
the polyp form include hydras and sea anemones. A
medusa is a flattened, mouth-down version of the polyp.
It moves freely in the water by a combination of passive
drifting and contractions of its bell-shaped body. An
example is a free-swimming jellyfish (called a “jellie).
The tentacles of a jellie dangle from the mouth area,
which points downward. Some cnidarians exist only as
polyps or only as medusae; others have both a medusa
stage and a polyp stage in their life cycle.
CNIDARIA
 Cnidarians are carnivores that use tentacles arranged in a
ring around their mouth to capture prey and to push
food into their gastrovascular cavity, where digestion
begins. The undigested remains are egested through the
mouth/anus. The tentacles are armed with batteries of
cnidocytes, unique cells that function in defense and the
capture of prey. Cnidocytes contain cnidae (from the
Greek word meaning nettle, or stinging thorn). A cnidae
is a capsule-like organelle that delivers a chemical sting.
Some cnidae have very long threads that stick to or
entangle small prey that bump into its tentacles.
BILATERIA
 C. BILATERIA (bilateral symmetry; all other
animals)
 The development of a head where sensory
structures are concentrated accompanied the
evolution of bilateral symmetry.
INVERTEBRATES
1. INVERTEBRATES
a) PLATYHELMINTHES (flatworms)
1) Trematoda (blood flukes)
2) Cestoda (tapeworms)
b) NEMATODA (roundworms)
c) ANNALIDA (segmented worms)
1) Oligochaetes (earthworms)
2) Hirudinea (leeches)
d) MOLLUSCA
1) Gastropods (snails and slugs)
2) Bivalves (clams, oysters, muscles, and scallops)
3) Cephalopods (octopuses and squid)
e) ARTHROPODA
1) Cheliceriforms (spiders)
2) Myriapods (millipedes and centipedes)
3) Insects
4) Crustaceans (crabs)
f) ECHINODERMS (starfish)
PLATYHELMINTHES
 PLATYHELMINTHES (flatworms)
 Flatworms have no radial symmetry; they live in
marine, fresh water, and damp earth habitats. In
addition to many free living forms, flatworms include
many parasitic species, such as flukes and tapeworms.
Flatworms are named because their bodies are thin; the
smallest are nearly microscopic, while some tapeworms
can be over 20 m long. Flatworms have no anus, but
have a highly branched gastrovascular cavity with only
one opening. Although there are four classes of
flatworms, we will only discuss the two that are
parasites: Trematoda and Cestoda.
Trematodes
 1) Trematodes (blood flukes) live as parasites in or on
other animals. Many have suckers for attaching to
internal organs or to the outer surfaces of the host.
Reproductive organs occupy nearly the entire interior of
these worms. Trematodes parasitize a wide range of
hosts. Many require an intermediate host in which
larvae develop before infecting the final host where the
adult worms live. For example, Trematodes that
parasitize humans spend part of their lives in snail hosts.
200 million people around the world are infected with
blood flukes. Individual flukes can survive in humans
for more than 40 years.
Cestoda
 2) Cestoda (tapeworms) are parasites that live
inside vertebrates, including humans. The anterior
end, or scolex, has suckers or hooks that lock the
worm to the intestinal lining of the host.
Tapeworms have no digestive tract of any sort, and
no gastrovascular cavity; they absorb nutrients
directly from the host intestine. The length of the
tapeworm is a long ribbon of units called
proglottids, which are sacs of sex organs. Mature
proglottids, loaded with thousands of eggs, are
released from the tail end of a mature tapeworm
and leave the host body in feces.
Cestoda
 If the feces contaminates food or water ingested by
other animals such as pigs or cattle, the tapeworm
eggs develop into larva that form cysts in the
muscles of these animals. Humans acquire these
larvae by eating undercooked meat, and the worms
develop into mature adults within the human.
Large tapeworms can block the intestines and rob
enough nutrients from the human host to cause
nutritional deficiencies.
NEMATODA
 NEMATODA (roundworms)
 Roundworms are among the most widespread of
all animals; they are found in most aquatic habitats,
in the soil, in moist tissues of plants, and in body
fluids and tissues of animals. They do not have a
segmented body. Their size ranges from 1 mm to
more than 1 m in length, tapering to a fine tip at the
posterior end. The body is covered by a tough coat
called a cuticle; as the worm grows it periodically
sheds the old cuticle and secretes a new, larger one.
NEMATODA
 Nematodes have a digestive canal, although they lack a
circulatory system. Nutrients are transported
throughout the body by way of a fluid. Nematodes have
muscles that produce a thrashing motion when they
contract.

 Nematode reproduction is sexual; the sexes are separate
and females are larger than males. A female may deposit
100,000 fertilized eggs per day. There are 25,000 known
species, most of which are not parasites and live in moist
soil and decomposing organic matter on the bottoms of
the lakes and oceans. They play an important role in
decomposition and nutrient cycling.
NEMATODA
 Many nematodes are important agricultural pests
that attack the roots of plants. Some nematodes
parasitize animals. Humans host at least 50
nematodes species, including pinworms and
hookworms. One notorious nematode is Trichenella,
the worm that causes trichinosis. Humans acquired
this nematode by eating undercooked infected pork
with juvenile worms and encyst in the muscle
tissue. Within the human intestine, the juveniles
develop into adults, burrow through the body and
travel to other organs, including muscles, where
they encyst.
ANNALIDA
 ANNALIDA (segmented worms)
 Annalida means “little rings”. They live in the sea,
fresh water, and damps soil. They range in length
from 1 mm to 3 m, the lakes of a giant Australian
earthworm. They are divided into three classes, but
we will discuss two: Oligochaetes (earthworms) and
Hirudinea (leeches).
Oligochaetes
 1) Oligochaetes (earthworms)
 Oligochaetes (“Oligo” means “few” and “chaetes”
means “hairs”) are named for their sparse bristles.
Earthworms eat their way through the soil,
extracting nutrients as the soil passes through the
digestive canal. Undigested material, mixed with
mucus secreted into the canal, is excreted through
the anus. Earthworms till the earth, adding to their
feces to improve the texture of the soil.
Oligochaetes
 Earthworms are hermaphrodites, but they crossfertilize. Two earthworms mate by aligning
themselves in such a way that they exchanged
sperm, and then they separate. The received sperm
are stored temporarily while an organ secretes a
mucus cocoon. The cocoon slides along the worm,
picking up the eggs and then the stored sperm. The
cocoon then slips off the worm’s head and remains
in the soil while the embryos develop. Some
earthworms can also reproduce a sexually by
fragmentation followed by regeneration.
Hirudinea
 2) Hirudinea (leeches)
 The majority of leeches inhabit freshwater, but there are
also marine and terrestrial leeches found in moist
vegetation. Some are parasites that suck blood by
attaching temporarily to other animals, including
humans. The host is usually oblivious to this attack
because the leach secretes an anesthetic. It then secretes
another chemical, hirudin, which prevents the blood
from coagulating. The parasite then sucks as much
blood as it can hold, often more than 10 times its own
weight. After the gorging, a leech can last for months
without another meal.
Hirudinea
 Until this century, leeches were frequently used for
blood-letting. It was thought that diseases were
carried in the blood, and if the blood was drained,
the patient would recover. Today they are used to
drain blood that accumulates in tissues following
certain injuries or surgeries. Researchers are also
investigating the potential use of hirudin to dissolve
unwanted blood clots that form during surgery or
as a result of heart disease.
MOLLUSCA
 MOLLUSCA (snails, clams, squid, octopus)
 Mollusks have a muscular foot, a visceral mass,
and a mantle. This category includes snails and
slugs, oysters and clams, and octopuses and squids.
Most mollusks are marine, though some inhabit
freshwater, and there are snails and slugs that live
on land. The term “mollusks” means “soft”, but
most mollusks are protected by a hard shell of
calcium carbonate. Slugs, squids, and octopuses
have a reduced internal shell or have lost their shell
completely during evolution.
MOLLUSCA
 The body of a mollusk has three main parts: a
muscular foot, used for movement; a visceral mass
containing most of the internal organs; and a
mantle, a fold of tissue that drapes over the visceral
mass and secretes a shell if one is present. Many
mollusks feed by using a strap-like rasping organ
called a radula to scrape up food. Most mollusks
have separate sexes, but many snails are
hermaphrodites. Their lifecycle usually includes a
larval stage.
Gastropods
 About three quarters of all mollusks are gastropods.
Most are marine, but garden snails and slugs are among
the gastropods that have adapted to land. Most
gastropods have a single, spiral shaped shell into which
the animal can retreat when threatened. They often have
a distinct head with eyes at the tips of its tentacles. They
move by a rippling motion of their foot. They use their
radula to graze on algae or plants. Several species,
however, are predators, and their radula is modified for
boring holes into the shells of other mollusks. In these
species, the teeth of the radula form poison darts that are
used to subdue prey.
Bivalves
 Another class of mollusks is the Bivalves, which include many
species of clams, oysters, muscles, and scallops. Bivalves have
a shell divided into two halves, hinged at the middle, and
powerful muscles to draw them tightly together. Bivalves
have no distinct head, and the radula has been lost. Some
bivalves have eyes and sensory tentacles along the outer edge
of their mantle. Most bivalves are suspension feeders. They
trap fine food particles in mucus that coats their gills, and cilia
(small hairs) sweep the particles into their mouth. Most
bivalves lead rather sedentary lives. Sessile muscles secrete
strong threads that tether them to rocks, docks, boats, and the
shells of other animals. However, clams can pull themselves
into the sand or mud, using their muscular foot for an anchor,
and scallops can skitter along the sea floor by flapping their
shelves, rather like the mechanical false teeth sold in novelty
shops.
Cephalopods
 3) Cephalopods
 Cephalopods are active predators. They use their
tentacles to grasp prey and their beak-like jaws to attack
and inject an immobilizing poison. The foot of a
cephalopod has become modified to include a muscular
siphon and parts of the tentacles and head (cephalopod
means “head-foot”). Most octopuses creep along the sea
floor in search of crabs and other food. Squids dart
about by drawing water into their cavity and then
firing a jet of water through their siphon like a water
balloon releasing. They change directions by pointing
the siphon in different directions.
Cephalopods
 The chambered Nautilus is the only cephalopod that still
has a shell. Cephalopods are the only mollusks with a
closed circulatory system, well developed sense organs,
and a complex brain. The ability to learn and behave in a
complex manner is probably more critical to fast-moving
predators then to sedentary animals such as clams. Most
species of squid are less than 75 cm long, but the giant
squids that live in the deep ocean may be larger than 20
m in length. These species feed on large fish; their
remains have been found in the stomachs of sperm
whales, which are probably their only natural predator.
ARTHROPODA
 ARTHROPODA (spiders, insects, crabs)
 Arthropods are segmented coclomates that have an
exoskeleton and jointed appendages. This includes
crustaceans, spiders, and insects. There are about a
billion billion arthropods in the world, most of which are
insects. The success of arthropods it's largely related to
their segmentation, hard exoskeleton, and jointed
appendages (arthropod means “jointed feet”).
Arthropod appendages are variously adapted for
walking, swimming, feeding, sensory reception,
copulation, and defense. This permits the division of
labor among different regions.
ARTHROPODA
 The body of an arthropod is completely covered by the cuticle,
an exoskeleton (external skeleton). The exoskeleton and it is
paper thin and flexible over the joints. The rigid exoskeleton
protects the animal and provides points of attachment for the
muscles that move the appendages. But it also means that an
arthropod cannot grow without occasionally shedding its
exoskeleton and producing a larger one. This process is called
molting, and it requires energy. The recently molted
arthropod is also vulnerable to dangers until its new, soft
exoskeleton hardens.

Arthropods have well-developed sensory organs, including
eyes, smell receptors, and antennae that function in both touch
and smell. These are concentrated at the head of the animal.
ARTHROPODA
 Like many mollusks, arthropods have an open
circulatory system in which the fluid called
hemolymph is propelled by a heart to the tissues
and organs. The term blood is reserved for fluid in a
closed circulatory system. A variety of organs
specialized for gas exchange exists in arthropods.
Most aquatic species have gills that allow for
increased surface area in contact with the
surrounding water from which they absorb oxygen.
Most insects have tracheal systems, which are
branched air ducts leading into the body. There are
four major groups of arthropods.
Cheliceriforms
 1) Cheliceriforms
 Cheliceriforms have claw-like feeding appendages called
chelicerae which serve as pinchers or fangs. Most of the
marine Cheliceriforms are extinct except for sea spiders
and horseshoe crabs. Most modern Cheliceriforms are
arachnids, a group that includes scorpions, spiders, ticks,
and mites.
 Ticks and mites are mainly parasitic arthropods. Nearly
all ticks are bloodsucking parasites on the body surfaces
of animals. Parasitic mites live on a variety of animals
and plants.
Arachnids
 Arachnids have a head that has six pairs of appendages:
chelicerae, a pair of appendages that function in sensing
or feeding, and four pairs of walking legs. Spiders use
their fang-like chelicerae, which are equipped with
poison glands, to attack prey. As the chelicerae chew the
prey, the spider spills digestive juices onto the torn
tissues. The food softens, and the spider sucks up the
liquid meal. A unique adaptation of many spiders is the
ability to catch insects by constructing webs out of silk, a
liquid protein produced by abdominal glands. The silk
is spun by organs called spinnerets into fibers that
solidify. Each spider engineers a style of web
characteristic of its species and builds it perfectly on the
first try.
Arachnids
 Various spiders also use silk in other ways: as a
drop line for rapid escape, as a cover for eggs, and
even as a gift wrap for food that males offer females
during courtship. Spider webs are more
lightweight, flexible, and waterproof than anything
known to man, and it is also many times stronger
than steel. Scientists want to synthesize it to make
rip-proof clothing, from children’s garments to
military uniforms. Scientists have spliced spider
venom genes into corn and other food crops as a
"natural pesticide" to deter insects and birds from
feeding on the plants.
Scorpions
 Scorpions have two appendages that are pinchers
specialized for defense and the capture of food. The
tip of the tail has a poisonous stinger. Scientists are
using scorpion venum for brain-cancer therapy.
Myriapods
 2) Myriapods
 Myriapods (many feet) include millipedes and
centipedes. They are all terrestrial (live on land).
Millipedes have a large number of legs, but fewer than
the “thousand” their name implies. Millipedes have
similar segments over most of the body. Each segment
has two pairs of legs. Millipedes eat decaying leaves and
other plant matter. Centipedes are carnivores. Each
segment has one pair of legs like the millipedes, but
centipedes have poison claws on their foremost trunk
segment that paralyze prey and aid in defense.
Insects
 Most insects have three body parts. They are the head,
thorax, and abdomen. Insects live in almost every terrestrial
habitat and in fresh water, and flying insects fill the air.
However, insects are rare in the oceans, where crustaceans are
the dominant arthropods. Flight is one key to the great
success of insects. An animal that can fly can escape many
predators, find food and mates, and disperse to new habitats
much faster than an animal that must crawl on the ground.
Many insects have one or two pairs of wings that emerge from
the thorax. Because the wings are extension of the cuticle and
not true appendages, insects can fly without sacrificing any
walking legs. By contrast, the flying vertebrates (birds and
bats) have one of their two pairs of walking legs modified into
wings and are generally quite clumsy on the ground.
Insects
 Dragonflies were among the first insects to fly. The
wings of bees and wasps are hooked together and
move as a single pair. Butterfly wings operate in a
similar fashion because the anterior pair overlaps
the posterior wings. In beetles, the posterior wings
function in flight, while the anterior ones are
modified as covers that protect the flight wings
when the beetle is on the ground or burrowing.
Insects
 Many insects undergo metamorphosis during their
development. In the incomplete metamorphosis of
grasshoppers, the young (called nymphs) resemble
adults but are smaller and lack wings. The nymph goes
through a series of molts, each time looking more like an
adult. Insects with complete metamorphosis have larval
stages specialized for eating and growing that are known
by such names as maggot, grub, or caterpillar. The larval
stage looks entirely different from the adult stage, which
is specialized for dispersal and reproduction.
Metamorphosis from the larval stage to the adult occurs
during a pupal stage. Although caterpillars chew on
leaves, moths and butterflies take in nectar by sucking
it through a tube consisting of modified mouthparts.
Insects
 Reproduction in insects is usually sexual, with
separate male and female individuals. Adults come
together and recognize each other as members of
the same species by advertising with bright colors
(butterflies), sound (crickets), or odors (moths).
Fertilization is generally internal. Sperm are
deposited directly into the female’s vagina in most
cases. Many insects mate only once in a lifetime.
After mating, a female often lays her eggs on an
appropriate food source where the next generation
can begin eating as soon as it hatches.
Insects
 Animals as numerous, diverse, and widespread as
insects are bound to affect the lives of all other
organisms, including humans. On the one hand, we
depend on bees, flies, and many other insects to pollinate
our crops. On the other hand, insects are carriers for
many diseases, including African sleeping sickness
(tsetse fly), and malaria (mosquitoes). Furthermore,
insects compete with humans for food: in parts of Africa
for instance, insects claim about 75% of the crops. Trying
to minimize their losses, farmers in the United States
spend billions of dollars each year on pesticides,
spraying crops with massive doses of some of the
deadliest poisons ever invented.
Crustaceans
 While arachnids and insects thrive on land,
crustaceans have remained in aquatic environments.
Crustaceans typically have branched appendages
that are extensively specialized. Lobsters and
crayfish, for instance, have a toolkit of 19 pairs of
appendages. The anterior most appendages are
antennae; crustaceans are the only arthropods with
two pairs. Three or more pairs of appendages are
modified as mouthparts, including the hard
mandibles. Walking legs are present in the thorax,
and unlike insects, crustaceans have appendages on
the abdomen. A lost appendage can be regenerated.
Crustaceans
 Sexes are separate in most crustaceans. In the case
of lobsters and crayfish, the male uses a specialized
pair of abdominal appendages to transfers sperm to
the female. Most aquatic crustaceans go through
one or more swimming larval stages.

 Some crustaceans are called isopods, which can be
found in water or on land. Among the terrestrial
isopods are the pill bugs, common on the
undersides of moist logs and leaves.
Crustaceans
 Lobster, crayfish, crabs, and shrimp are all called
the decapods. The cuticle of decapods is hardened
by calcium carbonate, forming a protective shield.
Most decapods are marine. Crayfish, however, live
in fresh water, and some tropical crabs live on land.
 Copepods are small crustaceans such as krill
(“whale food”), which live on algae. Krill are a
major food source for whales and humans, and are
also used as an agricultural fertilizer.
Crustaceans
 Barnacles are a group of mostly sessile crustaceans
whose cuticle is hardened into a shell. Most
barnacles anchor themselves to rocks, boat hulls,
and other submerged surfaces. The adhesive they
use is as strong as any synthetic glue. To feed, they
extend appendages from their shell to strain food
from the water. Other barnacles live as parasites
inside hosts such as crabs.
Crustaceans
 If barnacles are allowed to accumulate on a ship's
hull, the ship will travel slower in the water, or it
will have to burn more fuel to keep up its speed,
than it would otherwise. A six-month growth of
barnacles can result in having to burn 40 to 45
percent more fuel to maintain cruising speed.
Removing barnacles from ships' hulls costs ship
owners more than $125 million a year. Although
many new ideas have been tested, the best way to
keep barnacles from growing on a ship's hull is still
to paint the hull with copper bottom paint.
Crustaceans
 Barnacle cement, the substance the animals use to glue
themselves to ships' bottoms and to rocks, has attracted
the interest of doctors. A layer of this cement 3/10,000 of
an inch thick over one square inch will support a weight
of 7000 pounds. It is even stronger than epoxy cement.
At temperatures above 6000°F the glue will soften but
not melt, and at 380°F the cement will not crack. It does
not dissolve in most strong acids, bases, organic solvents,
or water. If man could learn to manufacture this cement,
which barnacles have been using for millions of years, it
could be used to mend broken bones and hold fillings in
teeth.
ECHINODERMATA
 ECHINODERMATA (starfish)
 Starfish and most other echinoderms (meaning “spiny
skin”) are slow moving or sessile marine animals. A thin
skin covers and endoskeleton of hard plates. They are
prickly from skeletal bumps and spines. Unique to
echinoderms is the water vascular system, a network of
canals that branch into the extensions called tube feet
that function in locomotion and eating. Sexual
reproduction of echinoderms usually involves separate
male and female individuals that release their gametes
into the water. The six classes of echinoderms are sea
stars, brittle stars, sea urchins and sand dollars, sea
lilies and feather stars, sea cucumbers, and sea daisies.