chapter: mollusks, worms, arthropods, echinoderms table of contents section 3: arthropodsarthropods...

Chapter: Mollusks, Worms, Arthropods, Echinoderms

Table of ContentsTable of Contents

Section 3: Arthropods

Section 1: Mollusks

Section 2: Segmented Worms

Section 4: Echinoderms

• 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.

Characteristics of Mollusks

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

• All mollusks have a thin layer of tissue called a mantle, which covers the body organs. These are located in the visceral (VIH suh rul) mass.

Body Plan

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Body Plan

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• Between the soft body and the mantle is a space called the mantle cavity. It contains gills—theorgans that exchange carbon dioxide for oxygen.

• 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 it’s added to throughout the life of the mollusk.

Body Plan

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• The inside layer also protects the soft body.

• 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.

Body Plan

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Body Plan

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• 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.

Classification of Mollusks

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• 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.

Gastropods

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• 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 teeth—to obtain food.

Gastropods

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• 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.

Bivalves

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

• Clams, oysters, and scallops are bivalve mollusks.

Bivalves

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

Bivalves

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• 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.

Cephalopods

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• 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.

Cephalopods

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• 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.

Cephalopods

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• 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.

Cephalopod Propulsion

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• 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 Newton’s 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.

Value of Mollusks

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• 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.

Value of Mollusks

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• 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.

11Section CheckSection Check

Question 1Which structure is responsible for exchanging carbon dioxide from the mollusk for oxygen in the water?


A. heartB. gills

C. mantleD. radula


AnswerThe answer is B. Gills are located in the mantle cavity.


Question 2Which structure is responsible for helping this organism move?


A. footB. mantle

C. Mantle cavityD. radula


Answer

The answer is A. Slugs and snails move by rhythmic contractions of the muscular foot.

Section CheckSection Check

Question 3

A squid is what type of mollusk?

A. bivalveB. cephalopodC. gastropodD. radula

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Section CheckSection Check

Answer

The answer is B. Cephalopods have large, well developed heads and their foot is divided into many tentacles.

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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.

Segmented WormsSegmented Worms

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Segmented Worm Characteristics

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

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


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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.


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

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.


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

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.


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

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

Circulation and Respiration• Earthworms have a closed circulatory system.


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• Two blood vessels meet in the front end of the earthworm andconnect to heartlike structures called aortic arches, which pump blood through the body.

Circulation and Respiration


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• Oxygen and carbon dioxides are exchanged through their skin, which is covered with a thin film ofwatery mucus.

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.


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• Earthworms respond to light, temperature, and moisture.

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 can’t fertilize its own eggs.


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

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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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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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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Leeches

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

• They feed on the blood of other animals.


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

Leeches• Leeches produce many

chemicals, including an anesthetic (a nus THEH tihk) that numbs the wound so you don’t 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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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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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.


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• 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.

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.


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

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

Origin of Segmented Worms• Mollusks and segmented worms may have a

common ancestor.


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• Their larvae are similar and are the best evidencethat they have a common ancestor.


Question 1Which letter corresponds with the setae?

A. AB. BC. CD. D


Answer

The answer is A. Setae are the bristlelike structures segmented worms use to hold onto soil and to move.


Question 2Which letter corresponds with the structures that pump blood through the body?

A. DB. EC. FD. G


AnswerThe answer is D. Earthworms have five aortic arches that pump blood throughout their bodies.


Question 3How are leeches valuable medically?

A. 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.


AnswerThe answer is A. Leeches are sometimes used after surgery to keep blood flowing to the repaired area.

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.

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

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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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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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.


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

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.


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

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.


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

Head• An insect’s head has a pair of antennae, eyes,

and a mouth.• The antennae are used for

touch and smell.


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

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

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.


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

• Flight also helps them escape from their predators.

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.


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

From Egg to Adult

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


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• Many insects go through changes in body form calledmetamorphosis (me tuh MOR fuh sihs).

From Egg to Adult• Many insects—butterflies, beetles, ants, bees,

moths, and flies—undergo complete metamorphosis.

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


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Click box to view movie.

Obtaining Food• Grasshoppers and ants have large mandibles

(MAN duh bulz) for chewing plant tissue.


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• Butterflies and honeybees are equipped with siphons forlapping up nectar in flowers.

Obtaining Food• Praying mantises eat other

animals.• External parasites, such as

mosquitoes, fleas, and lice, drink the blood and body fluids of other animals.


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

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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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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Arachnids• Spiders, scorpions, mites, and ticks are

examples of arachnids (uh RAK nudz).


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• They have two body regions—a head-chest region called the cephalothorax (se fuh luhTHOR aks) and an abdomen.

Arachnids


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• 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.

Scorpions• Arachnids that have a sharp, venom-filled

stinger at the end of their abdomen are called scorpions.


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• Unlike other arachnids, scorpions have a pair of well-developed appendages—pincers—with which they grab their prey.

Spiders

• Because spiders can’t chew their food, they release enzymes into their prey that help digest it, then sucks it back into its mouth.


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Spiders


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• 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.

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.


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

• Ticks attach to their host’s skin and remove blood through specialized mouthparts.

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

Centipedes and Millipedes• Two groups of arthropods—centipedes

and millipedes—have long bodies with many segments and many legs, antennae, and simple eyes.


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• 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.

Centipedes and Millipedes• Centipedes hunt for their prey, which

includes snails, slugs, and worms.


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• 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.

Crustaceans• Crabs, crayfish,

shrimp, barnacles, pill bugs, and water fleas are crustaceans.


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

• Crustaceans haveone or tow pairs of antennae and mandibles, which are used for crushing food.

Crustaceans• Crustaceans have five pairs of legs.


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• 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.

Value of Arthropods• Arthropods are a source of food for many

animals, including humans.


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

• Bees manufacture honey, and silkworms produce silk.

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

Value of Arthropods• Not all arthropods are useful to humans.

Almost every cultivated crop has some insect pest that feeds on it.


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• Many arthropods—mosquitoes, tsetse flies, fleas, and ticks—carry human and other animal diseases.

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

Controlling Insects

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


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• 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.

Controlling Insects

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


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

Origin of Arthropods• Because of their hard body parts, arthropod

fossils are among the oldest and best-preserved fossils of many-celled animals.


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


Question 1

The word arthropoda means_______.

A. many bristlesB. head-footedC. little ringsD. jointed foot


Answer

The answer is D. Crabs are an example of an arthropod.


Question 2

Which is NOT one of the three body regions of an insect?

A. abdomenB. appendageC. headD. thorax


Answer

The answer is B. Insect bodies consist of a head, thorax, and abdomen.


Question 3

Which is an arachnid?

A. butterflyB. conch C. earthwormD. tick


Answer

The answer is D. Arachnids have two body regions and four pairs of legs, but no antennae.

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.

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

Echinoderm Characteristics• All echinoderms have a

mouth, stomach, and intestines.

• They feed on a variety of plants and animals.


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• 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.

Water-Vascular System• A characteristic unique to echinoderms is

their water-vascular system.


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

Water-Vascular System


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

Water-Vascular System• Tube feet are hollow, thin-walled tubes that

each end in a suction cup.


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

Types of Echinoderms

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

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


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• The arms are lined with thousands of tube feet.

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

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.


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• Sea stars also can repair themselves by regeneration.

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

Brittle Stars• Brittle stars have fragile, slender, branched

arms that break off easily.• This adaption helps a brittle star survive

attacks by predators.


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• 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.

Sea Urchins and Sand Dollars• Sea urchins, sea biscuits, and sand dollars

are disk- or globe-shaped echinoderms covered with spines.


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• 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.

Sea Cucumbers

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


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

Value of Echinoderms

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


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

Value of Echinoderms


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• 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.

Origin of Echinoderms


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• 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.

Origin of Echinoderms


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• 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.

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.


Answer

The answer is water-vascular system. The water-vascular system is unique to echinoderms.


Question 2Which letter corresponds with the tube feet?


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.



Question 3

Which is a survival tactic of an echinoderm?

A. arms break off easilyB. jet propulsion C. pinchersD. venom


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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