Chapter: Mollusks, Worms,

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Table of Contents
Chapter Mollusks, Worms,
Arthropods, Echinoderms
Section 1 Mollusks
Section 2 Segmented Worms
Section 3 Arthropods
Section 4 Echinoderms
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Mollusks
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Characteristics of Mollusks

• Mollusks (MAH lusks) are soft-bodied
  invertebrates with bilateral symmetry and usually
  one or two shells.

• Their organs are in a fluid-filled cavity.

• Most mollusks live in water, but some live on
  land.

• Snails, clams, and squid are examples of mollusks.

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Mollusks
1
Body Plan
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Mollusks
1
Body Plan
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Mollusks
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Body Plan

• The mantle also secretes the shell or protects
  the body if the mollusk does not have a shell.

• The shell is made up of several layers.

• The inside layer is the smoothest. It is usually
  the thickest layer because its added to
  throughout the life of the mollusk.

• The inside layer also protects the soft body.

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Mollusks
1
Body Plan

• Most mollusks have an open circulatory system in
  which the heart moves blood out into the open
  spaces around the body organs.

• The blood, completely surrounds and nourishes the
  body organs.

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Mollusks
1
Body Plan

• Most mollusks have a well-developed head with a
  mouth and some sensory organs.

• Some mollusks have tentacles.

• On the underside of a mollusk is the muscular
  foot, which is used for movement.

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Mollusks
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Classification of Mollusks

• Mollusks that have shells are then classified by
  the kind of shell and kind of foot that they have.

• The three most common groups of mollusks are
  gastropods, bivalves, and cephalopods.

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Mollusks
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Gastropods

• The largest group of mollusks, the gastropods,
  includes snails, conchs, abalones, whelks, sea
  slugs, and garden slugs.

• Gastropods use a radula (RA juh luh)a tonguelike
  organ with rows of teethto obtain food.

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Mollusks
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Gastropods

• Slugs and many snails are adapted to life on land.

• They move by rhythmic contractions of the
  muscular foot.

• Glands in the foot secrete a layer of mucus on
  which they slide.

• Slugs do not have shells but are protected by a
  layer of mucus instead, so they must live in
  moist places.

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Mollusks
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Bivalves

• Mollusks that have a hinged, two-part shell
  joined by strong muscles are called bivalves.

• Clams, oysters, and scallops are bivalve mollusks.

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Mollusks
1
Bivalves

• These animals pull their shells closed by
  contracting powerful muscles near the hinge. To
  open their shells, they relax these muscles.

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Mollusks
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Bivalves

• For protection, clams burrow deep into the sand
  by contracting and relaxing their muscular foot.

• Mussels and oysters attach themselves with a
  strong thread or cement to a solid surface. This
  keeps waves and currents from washing them away.

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Mollusks
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Cephalopods

• The most specialized and complex mollusks are the
  cephalopods (SE fuh luh pawdz), which includes
  squid, octopuses, cuttlefish, and chambered
  nautiluses.

• Cephalopods have a large, well-developed head.

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Mollusks
1
Cephalopods

• Their foot is divided into many tentacles with
  strong suction cups or hooks for capturing prey.

• All cephalopods are predators. They feed on fish,
  crustaceans, worms, and other mollusks.

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Mollusks
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Cephalopods

• Squid and octopuses have a well-developed nervous
  system and large eyes similar to human eyes.

• Unlike other mollusks, cephalopods have a closed
  circulatory system, in which blood containing
  food and oxygen moves through the body in a
  series of closed vessels.

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Mollusks
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Cephalopod Propulsion

• Squid and other cephalopods have a water-filled
  cavity between an outer muscular covering and its
  internal organs.

• When the cephalopod tightens its muscular
  covering, water is forced out through an opening
  neat the head.

• According to Newtons third law of motion, when
  one object exerts a force on a second object, the
  second object exerts a force on the first that is
  equal and opposite in direction.

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Mollusks
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Value of Mollusks

• Many people make their living raising or
  collecting mollusks to sell for food.

• Many mollusk shells are used for jewelry and
  decoration.

• Pearls are produced by several species of
  mollusks.

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Mollusks
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Value of Mollusks

• Even though mollusks are beneficial in many ways,
  they also can cause problems for humans.

• Land slugs and snails damage plants.

• Certain species of snails are hosts of parasites
  that infect humans.

• Eating infected mollusks can result in sickness
  or even death.

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Section Check
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Question 1
Which structure is responsible for exchanging
carbon dioxide from the mollusk for oxygen in the
water?
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Section Check
1
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Section Check
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Answer
The answer is B. Gills are located in the mantle
cavity.
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Section Check
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Question 2
Which structure is responsible for helping this
organism move?
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Section Check
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Section Check
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Answer
The answer is A. Slugs and snails move by
rhythmic contractions of the muscular foot.
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Section Check
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Question 3
A squid is what type of mollusk?
A. bivalve B. cephalopod C. gastropod D. radula
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Section Check
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Answer
The answer is B. Cephalopods have large, well
developed heads and their foot is divided into
many tentacles.
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Segmented Worms
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Segmented Worm Characteristics

• Annelids (A nuh ludz) have tube-shaped bodies
  that are divided into many segments.

• On the outside of each body segment are
  bristlelike structures called setae (SEE tee).

• Segmented worms use their setae to hold on to the
  soil and to move.

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Segmented Worms
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Segmented Worm Characteristics

• Segmented worms also have bilateral symmetry, a
  body cavity that holds the organs, and two body
  openingsa mouth and an anus.

• Earthworms, marine worms, and leeches are
  examples of annelids.

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Segmented Worms
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Earthworm Body Systems

• The most well-known annelids are earthworms. They
  have a definite anterior, or front end, and a
  posterior, or back end.

• Earthworms have more than 100 body segments. The
  segments can be seen on the outside and the
  inside of the body cavity.

• Each body segment, except for the first and last
  segments, has four pairs of setae.

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Segmented Worms
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Digestion and Excretion

• As an earthworm burrows through the soil, it
  takes soil into its mouth.

• The soil ingested by an earthworm moves to the
  crop, which is a sac used for storage.

• Behind the crop is a muscular structure called
  the gizzard, which grinds the soil and the bits
  of organic matter.

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Segmented Worms
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Digestion and Excretion

• This ground material passes to the intestine,
  where the organic matter is broken down and the
  nutrients are absorbed by the blood.

• Wastes leave the worm through the anus.

• Their wastes pole up at the openings to their
  burrows.

• These piles are called castings which help
  fertilize the soil.

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Segmented Worms
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Circulation and Respiration

• Earthworms have a closed circulatory system.

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Segmented Worms
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Circulation and Respiration
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Segmented Worms
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Nerve Response and Reproduction

• Earthworms have a small brain in their front
  segment.

• Nerves in each segment join to form a main nerve
  cord that connects to the brain.

• Earthworms respond to light, temperature, and
  moisture.

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Segmented Worms
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Nerve Response and Reproduction

• Earthworms are hermaphrodites (hur MA fruh
  dites)meaning they produce sperm and eggs in the
  same body.

• Even though each worm has male and female
  reproductive structures, an individual worm cant
  fertilize its own eggs.

• Instead, it has to receive sperm from another
  earthworm in order to reproduce.

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Segmented Worms
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Marine Worms

• More than 8,000 species of marine worms, or
  polychaetes, (PAH lee keets) exist.

• Polchaetes, like earthworms, have segments with
  setae. However, the setae occur in bundles on
  these worms.

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Segmented Worms
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Marine Worms

• Sessile, bottom-dwelling polychaetes, have
  specialized tentacles that are used for
  exchanging oxygen and carbon dioxide and
  gathering food.

• Some marine worms build tubes around their bodies
  and retreat into their tubes when startled.

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Segmented Worms
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Marine Worms

• Free-swimming polychaetes have a head with eyes,
  a tail, and parapodia (per uh POH dee uh).

• Parapodia are paired, fleshy outgrowths which aid
  in feeding and locomotion.

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Segmented Worms
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Leeches

• Leeches are segmented worms, but their bodies are
  not as round or as long as earthworms are, and
  they dont have setae.

• They feed on the blood of other animals.

• A sucker at each end of a leechs body is used to
  attach itself to an animal.

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Segmented Worms
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Leeches

• Leeches produce many chemicals, including an
  anesthetic (a nus THEH tihk) that numbs the wound
  so you dont feel its bite.

• After the leech has attached itself, it cuts into
  the animal and sucks out two to ten times its own
  weight in blood.

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Segmented Worms
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Leeches and Medicine

• Sometimes, leeches are used after surgery to keep
  blood flowing to the repaired area.

• Besides the anti-clotting chemical, leech saliva
  also contains a chemical that dilates blood
  vessels, which improves the blood flow and allows
  the wound to heal more quickly.

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Segmented Worms
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Value of Segmented Worms

• Earthworms help aerate the soil by constantly
  burrowing through it.

• Earthworms speed up the return of nitrogen and
  other nutrients to the soil for use by plants.

• Researchers are developing drugs based on the
  chemicals that come from leeches because leech
  saliva prevents blood clots.

• Marine worms and their larvae are food for many
  fish, invertebrates, and mammals.

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Segmented Worms
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Origin of Segmented Worms

• Some scientists hypothesize that segmented worms
  evolved in the sea.

• The fossil record for segmented worms is limited
  because of their soft bodies.

• The tubes of marine worms are the most common
  fossils of the segmented worms.

• Some of these fossils date back about 620 million
  years.

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Segmented Worms
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Origin of Segmented Worms

• Mollusks and segmented worms may have a common
  ancestor.

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Section Check
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Question 1
Which letter corresponds with the setae?
A. A B. B C. C D. D
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Section Check
2
Answer
The answer is A. Setae are the bristlelike
structures segmented worms use to hold onto soil
and to move.
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Section Check
2
Question 2
Which letter corresponds with the structures that
pump blood through the body?
A. D B. E C. F D. G
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Section Check
2
Answer
The answer is D. Earthworms have five aortic
arches that pump blood throughout their bodies.
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Section Check
2
Question 3
How are leeches valuable medically?

• Chemicals in their saliva prevent blood
• from clotting.
• B. Leeches act as blood transfusers.
• C. Leeches prevent pain from occurring in
• major wounds.
• D. Leeches filter and purify blood.

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Section Check
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Answer
The answer is A. Leeches are sometimes used
after surgery to keep blood flowing to the
repaired area.
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Arthropods
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Characteristics of Arthropods

• There are more than a million different species
  of arthropods, (AR thruh pahdz).

• The jointed appendages of arthropods can include
  legs, antennae, claws, and pincers.

• Arthropods also have bilateral symmetry,
  segmented bodies, an exoskeleton, a body cavity,
  a digestive system with two openings, and a
  nervous system.

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Arthropods
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Characteristics of Arthropods

• Most arthropods species have separate sexes and
  reproduce sexually.

• Arthropods are adapted to living in almost every
  environment.

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Arthropods
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Segmented Bodies

• The bodies of arthropods are divided into
  segments.

• Some arthropods have many segments, but others
  have segments that are fused together to form
  body regions, such as those of insects, spiders,
  and crabs.

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Arthropods
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Exoskeletons

• All arthropods have a hard, outer covering called
  an exoskeleton.

• It covers, supports, and protects the internal
  body and provides places for muscles to attach.

• In many land-dwelling arthropods, such as
  insects, the exoskeleton has a waxy layer that
  reduces water loss from the animal.

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Arthropods
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Exoskeletons

• An exoskeleton cannot grow as the animal grows.

• From time to time, the exoskeleton is shed and
  replaced by a new one in a process called molting.

• While the animals are molting, they are not well
  protected from predators because the new
  exoskeleton is soft.

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Arthropods
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Insects

• More species of insects exist then all other
  animal groups combined.

• More than 700,000 species of insects have been
  classified, and scientists identify more each
  year.

• Insects have three body regionsa head, a thorax,
  and an abdomen.

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Arthropods
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Head

• An insects head has a pair of antennae, eyes,
  and a mouth.

• The antennae are used for touch and smell.

• The eyes are simple or compound. Simple eyes
  detect light and darkness.

• Compound eyes contain many lenses and can detect
  colors and movement.

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Arthropods
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Thorax

• Three pairs of legs and one or two pairs of
  wings, if present, are attached to the thorax.

• Insects are the only invertebrate animals that
  can fly.

• Flying allows insects to find places to live,
  food sources, and mates.

• Flight also helps them escape from their
  predators.

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Arthropods
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Abdomen

• The abdomen is where the reproductive structures
  are found.

• Insects have an open circulatory system that
  carries digested food to cells and removes wastes.

• Insects have openings called spiracles (SPIHR ih
  kulz) on the abdomen and thorax through which air
  enters and waste gases leave the insects body.

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Arthropods
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From Egg to Adult

• Grasshoppers, silverfish, lice, and crickets
  undergo incomplete metamorphosis.

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Arthropods
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From Egg to Adult

• Many insectsbutterflies, beetles, ants, bees,
  moths, and fliesundergo complete metamorphosis.

• The stages of complete metamorphosis are egg,
  larva, pupa, and adult.

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Arthropods
3
Obtaining Food

• Grasshoppers and ants have large mandibles (MAN
  duh bulz) for chewing plant tissue.

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Arthropods
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Obtaining Food

• Praying mantises eat other animals.

• External parasites, such as mosquitoes, fleas,
  and lice, drink the blood and body fluids of
  other animals.

• Silverfish eat things that contain starch and
  some moth larvae eat wool clothing.

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Arthropods
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Insect Success

• Most insects have short life spans, so genetic
  traits can change more quickly in insect
  populations than in organisms that take longer to
  reproduce.

• Because insects generally are small, they can
  live in a wide range of environments and avoid
  their enemies.

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Arthropods
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Insect Success

• Many species of insects can live in the same area
  and not compete with one another for food,
  because many are so specialized in what they eat.

• Protective coloration, or camouflage, allows
  insects to blend in with their surroundings.

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Arthropods
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Arachnids

• Spiders, scorpions, mites, and ticks are examples
  of arachnids (uh RAK nudz).

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Arthropods
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Arachnids

• Arachnids have four pairs of legs but no antennae.

• Many arachnids are adapted to kill prey with
  venom glands, stingers, or fangs.

• Others are parasites.

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Arthropods
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Scorpions

• Arachnids that have a sharp, venom-filled stinger
  at the end of their abdomen are called scorpions.

• Unlike other arachnids, scorpions have a pair of
  well-developed appendagespincerswith which they
  grab their prey.

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Arthropods
3
Spiders

• Because spiders cant chew their food, they
  release enzymes into their prey that help digest
  it, then sucks it back into its mouth.

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Arthropods
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Spiders

• Oxygen and carbon dioxide are exchanged in book
  lungs.

• Openings on the abdomen allow these gases to move
  into and out of the book lungs.

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Arthropods
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Mites and Ticks

• Most mites are animal or plant parasites, but
  some are not like the mites that live in the
  follicles of human eyelashes.

• Most mites are so small that they look like tiny
  specs to the unaided eye.

• Ticks attach to their hosts skin and remove
  blood through specialized mouthparts.

• Diseases carried by ticks include Lyme disease
  and Rocky Mountain spotted fever.

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Arthropods
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Centipedes and Millipedes

• Two groups of arthropodscentipedes and
  millipedeshave long bodies with many segments
  and many legs, antennae, and simple eyes.

• They can be found in damp environments, including
  in woodpiles, under vegetation, and in basements.

• Centipedes and millipedes reproduce sexually.
  They make nests for their eggs and stay with them
  until the eggs hatch.

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Arthropods
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Centipedes and Millipedes

• Centipedes hunt for their prey, which includes
  snails, slugs, and worms.

• They have a pair of venomous claws that they use
  to inject venom into their prey.

• Millipedes feed on plants and decaying material
  and often are found under the damp plant material.

Click image to view movie.
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Arthropods
3
Crustaceans

• Crabs, crayfish, shrimp, barnacles, pill bugs,
  and water fleas are crustaceans.

• Most crustaceans live in water, but some live in
  moist environments on land.

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Arthropods
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Crustaceans

• Crustaceans have five pairs of legs.

• The first pair of legs are claws that catch and
  hold food.

• The other four pairs are walking legs.

• They also have five pairs of appendages on the
  abdomen called swimmerets.

• If a crustacean loses an appendage, it will grow
  back, or regenerate.

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Arthropods
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Value of Arthropods

• Arthropods are a source of food for many animals,
  including humans.

• Bees, butterflies, moths, and flies pollinate
  crops.

• Bees manufacture honey, and silkworms produce
  silk.

• Many insects and spiders are predators of harmful
  animal species.

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Arthropods
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Value of Arthropods

• Not all arthropods are useful to humans. Almost
  every cultivated crop has some insect pest that
  feeds on it.

• Many arthropodsmosquitoes, tsetse flies, fleas,
  and tickscarry human and other animal diseases.

• In addition, weevils, cockroaches, carpenter
  ants, clothes moths, termites, and carpet beetles
  destroy food, clothing, and property.

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Arthropods
3
Controlling Insects

• One common way to control problem insects is by
  insecticides.

• However, many insecticides also kill helpful
  insects.

• Another problem is that many toxic substances
  that kill insects remain in the environment and
  accumulate in the bodies of animals that eat them.

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Arthropods
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Controlling Insects

• Different types of bacteria, fungi, and viruses
  are being used to control some insect pests.

• Other biological controls include using sterile
  males or naturally occurring chemicals that
  interfere with the reproduction or behavior of
  insect pests.

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Arthropods
3
Origin of Arthropods

• Because of their hard body parts, arthropod
  fossils are among the oldest and best-preserved
  fossils of many-celled animals.

• Scientists hypothesize that arthropods probably
  evolved from an ancestor of segmented worms.

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Section Check
3
Question 1
The word arthropoda means_______.
A. many bristles B. head-footed C. little
rings D. jointed foot
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Section Check
3
Answer
The answer is D. Crabs are an example of an
arthropod.
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Section Check
3
Question 2
Which is NOT one of the three body regions of an
insect?
A. abdomen B. appendage C. head D. thorax
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Section Check
3
Answer
The answer is B. Insect bodies consist of a
head, thorax, and abdomen.
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Section Check
3
Question 3
Which is an arachnid?
A. butterfly B. conch C. earthworm D. tick
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Section Check
3
Answer
The answer is D. Arachnids have two body regions
and four pairs of legs, but no antennae.
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Echinoderms
4
Echinoderm Characteristics

• Echinoderm (ih KI nuh durm) are found in oceans
  all over the world.

• Echinoderms have a hard endoskeleton covered by a
  thin, bumpy, or spiny epidermis.

• They are radically symmetrical, which allows them
  to sense food, predators, and other things in
  their environment from all directions.

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Echinoderms
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Echinoderm Characteristics

• All echinoderms have a mouth, stomach, and
  intestines.

• They feed on a variety of plants and animals.

• Others feed on dead and decaying matter called
  detritus (de TRI tus) found on the ocean floor.

• Echinoderms have no head or brain, but they do
  have a nerve ring that surrounds the mouth.

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Echinoderms
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Water-Vascular System

• A characteristic unique to echinoderms is their
  water-vascular system.

• It allows them to move, exchange carbon dioxide
  and oxygen, capture food, and release wastes.

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Echinoderms
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Water-Vascular System

• The water-vascular system is a network of
  water-filled canals with thousands of tube feet
  connected to it.

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Echinoderms
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Water-Vascular System

• Tube feet are hollow, thin-walled tubes that each
  end in a suction cup.

• As the pressure in the tube feet changes, the
  animal is able to move along by pushing out and
  pulling in its tube feet.

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Echinoderms
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Types of Echinoderms

• Approximately 6,000 species of echinoderms are
  living today.

• Of those, more than one-third are sea stars.

• The arms are lined with thousands of tube feet.

• Sea stars use their tube feet to open the shells
  of their prey.

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Echinoderms
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Types of Echinoderms

• Sea stars reproduce sexually when females release
  eggs and males release sperm into the water.

• Females can produce millions of eggs in one
  season.

• Sea stars also can repair themselves by
  regeneration.

• If a sea star loses an arm, it can grow a new one.

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Echinoderms
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Brittle Stars

• Brittle stars have fragile, slender, branched
  arms that break off easily.

• This adaption helps a brittle star survive
  attacks by predators.

• Brittle stars quickly regenerate lost parts.

• They live hidden under rocks or in litter on the
  ocean floor.

• Brittle stars use their flexible arms for
  movement instead of their tube feet.

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Echinoderms
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Sea Urchins and Sand Dollars

• Sea urchins, sea biscuits, and sand dollars are
  disk- or globe-shaped echinoderms covered with
  spines.

• Some sea urchins have sacs near the end of the
  spines that contain toxic fluid that is injected
  into predators.

• The spines also help in movement and burrowing.

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Echinoderms
4
Sea Cucumbers

• Sea cucumbers are soft-bodied echinoderms that
  have a leathery covering.

• They have tentacles around their mouth and rows
  of tube feet on their upper and lower surfaces.

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Echinoderms
4
Value of Echinoderms

• Echinoderms are important to the marine
  environment because they feed on dead organisms
  and help recycle materials.

• Sea urchins control the growth of algae in
  coastal areas.

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Echinoderms
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Value of Echinoderms

• Sea urchin eggs and sea cucumbers are used for
  food in some places.

• Many echinoderms are used in research and some
  might be possible sources of medicines.

• Sea stars are important predators that control
  populations of other animals.

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Echinoderms
4
Origin of Echinoderms

• A good fossil record exists for echinoderms.

• Echinoderms date back more than 400 million years.

• The earliest echinoderms might have had bilateral
  symmetry as adults and may have been attached to
  the ocean floor by stalks.

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Echinoderms
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Origin of Echinoderms

• Scientists hypothesize that echinoderms more
  closely resemble animals with backbones than any
  other group of invertebrates.

• This is because echinoderms have complex body
  systems and an embryo that develops the same way
  that the embryos of animals with backbones
  develop.

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Section Check
4
Question 1
In echinoderms, the _______ is a network of
water-filled canals with thousands of tube feet
connected to it which allows for movement,
exchange of carbon-dioxide and oxygen, capture of
food and release of waste.
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Section Check
4
Answer
The answer is water-vascular system. The
water-vascular system is unique to echinoderms.
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Section Check
4
Question 2
Which letter corresponds with the tube feet?
106
Section Check
4
Answer
The letter C represents the tube feet. Tube feet
are hollow, thin-walled tubes that each end in
suction cup. They allow sea stars to move.
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Section Check
4
Question 3
Which is a survival tactic of an echinoderm?
A. arms break off easily B. jet propulsion C.
pinchers D. venom
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Section Check
4
Answer
The answer is A. Brittle stars have arms that
break off easily if they are grabbed by a
predator, allowing for escape. The lost parts
regenerate quickly.
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