Download animals, invertebrates

ANIMALS, 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 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 are prokaryotes (do not have a nucleus). Plants, fungi, and animals are
eukaryotes (have a nucleus). 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.
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.
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.
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
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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 like slicing a pie. 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.
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
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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.
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.
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.
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.
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 penicillinresistant 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.
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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.
There are two variations on this body plan: the sessile polyp and the floating medusa.
Polyps are cylinder-shaped 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.
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.
C. BILATERIA (bilateral symmetry; all other animals)
The development of a head where sensory structures are concentrated accompanied
the evolution of bilateral symmetry.
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, mussels, 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)
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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.
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.
2) Cestoda (tapeworms) are parasites that live inside vertebrates, including humans.
The anterior end, or scolex (head), 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. 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 (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.
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
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matter on the bottoms of the lakes and oceans. They play an important role in
decomposition and nutrient cycling.
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 (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).
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. 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.
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.
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.
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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. 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.
1) 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.
2) Bivalves
Another class of mollusks is the Bivalves, which include many species of clams, oysters,
mussels, 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 mussels 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.
3) Cephalopods (octopus, squids, nautilus)
Cephalopods are active predators. They use their tentacles to grasp prey and their beaklike 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. 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
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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 (spiders, insects, crabs)
Arthropods are segmented and 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.
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.
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.
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 blood-sucking parasitic arthropods. Nearly all ticks are
bloodsucking parasites on the body surfaces of animals. Parasitic mites live on a variety
of animals and plants.
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Arachnids (spiders) 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. 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 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 venom
for brain-cancer therapy.
2) Myriapods (centipedes and millipedes)
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.
3) 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.
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.
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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.
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.
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.
4) 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.
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 (feet look the same), 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.
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Lobster, crayfish, crabs, and shrimp are all called the decapods (ten feet). 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 (oar feet) 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.
Barnacles are a group of mostly sessile (stay anchored onto something) 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.
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.
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 (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.
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