CHAPTER 14

Mollusks, Annelids,

Arthropods, and

Echinoderms

Mrs. Nell’s 7th Grade Life Science Class

Kingdom- Animalia

Phylum- Mollusca

Mollusks

Mollusks are the soft-bodied invertebrates in the phylum Mollusca. Mollusks usually have shells (not the slug, though) and bilateral symmetry.

The Body of a Mollusk

Mollusks have a soft body covered by a mantle (a thin layer of tissue that makes the shell or protects the body if the mollusk doesn’t have a shell).

Mollusk GillsMollusks have gills to exchange oxygen and CO2 with the

water.

gills

Visceral Mass

The body organs are located together in what is called the visceral mass.

Mollusk Foot

Mollusks have a muscular foot for movement.

Circulatory System

Mollusks have an open circulatory system (blood isn’t contained in vessels- blood bathes the mollusk’s organs).

Classifying Mollusks

There are three main classes of mollusks:

1) Gastropods

2) Bivalves

3) Cephalopods

GastropodsGastropods or univalves are the largest class of mollusks. Except for slugs, each has a single shell. Members of the gastropod class are:

• Snails• Slugs• Abalones• Whelks• Sea slugs• Conches

Nutrition

Gastropods feed on plant material using their radula (a tongue like organ with rows of teeth that works like a file).

Bivalves

Bivalves are mollusks with a two-part shell joined by a hinge. Bivalves use siphons to filter feed. Some bivalves are:

• Clams• Oysters• Scallops

Bivalve Defense

To protect themselves, clams will borrow deep into the sand with their muscular foot. Mussels and oysters will cement themselves to a surface. Scallops will open and close their shell rapidly to move away quickly.

CephalopodsCephalopods have a large, well-developed head. They have tentacles with strong suckers for capturing prey. They have a well developed nervous system and large eyes. Cephalopods have closed circulatory systems, unlike other mollusks.

Some cephalopods are:• Squid• Octopus• Chambered nautilus

Jet Propulsion

Cephalopods move by pushing water out through an opening in their head. This jet of water sends it backward. A squid can move more than 60m/s this way.

Squid Internal Anatomy

Importance of Mollusks (I)

Mollusks provide food for fish, sea stars, birds, and other organisms.

Importance of Mollusks (II)

Some invertebrates, like the hermit crab, use empty mollusk shells as shelter.

Importance of Mollusks (III)

Clams, oysters, snails, and scallops are used for food.

Importance of Mollusks (IV)

Pearls are produced by many species of mollusks.

Kingdom- Animalia

Phylum- Annelida

Segmented Worms

Segmented worms belong to the Phylum Annelida. Annelid means “little rings” and describes the segments that makeup the body of these worms. Some members of the annelid phylum are…

• Earthworm• Leeches• Marine Worms

Segmented Worms & Mollusks

Like mollusks, all segmented worms have a body cavity that holds their organs.

Setae

On the outside of each segment, annelids have little bristle-like structures called setae that help them move. Segmented worms also use the setae to help them stay in the soil if a bird gets a hold of them!

Earthworms

Earthworms eat soil. They use their crop for storage and their gizzard to grind the soil. Digested food moves to the intestine where it is broken down and absorbed by the blood. Undigested soil and waste leave the worm through the anus.

Leeches

The "medicinal leech" feeding on blood from a human arm.

Leeches feed on the blood of animals- including humans. They have two suckers that they use to attach to the animal. It will then cut into the flesh and suck out blood. Leeches produce an anesthetic so that the animal doesn’t feel the bite.

For centuries leeches were used for blood letting because of the mistaken belief that bodily disorders and fevers were caused by an excess of blood.

Today leeches are used to keep blood flowing to reattach body parts.

Marine WormsMarine worms also have segments with setae. Some marine worms trap food in tentacles. Others build tubes to hide in.

Annelids & Mollusks- related?

Scientists think segmented worms and mollusks share a common ancestor. They were the first of the animal groups to have bodies with space for the body organs, and they both have a larva stage early in their development.

Kingdom- AnimaliaPhylum-

Arthropoda

ARTHROPODSArthropods make up the largest phylum of animals in the animal kingdom. Members of the arthropod phylum include…

• Insects• Arachnids• Centipedes• Millipedes• Crustaceans

Molting Caterpillar

The Body of an Arthropod

Arthropoda means “jointed foot” and describes the jointed appendages of arthropods. The appendages on an arthropod include legs antennae, claws, and pinchers.

Arthropods and segmented worms- related?

The bodies of arthropods are divided into segments like those of segmented worms so scientists hypothesize they may have a common ancestor.

Exoskeletons

All arthropods have an external covering called the exoskeleton that protects the body. It is made of protein and a carbohydrate called chitin. Once the arthropod outgrows its shell it will molt.

Kingdom- AnimaliaPhylum- Arthropoda

Class- Insecta

Insects

Insects have three body regions: a head, thorax, and an abdomen. The head has a pair of antennae, eyes, and a mouth. The thorax has three pairs of jointed legs and sometimes wings. The abdomen doesn’t have wings or legs attached.

The Body of an Insect

Insects have open circulatory systems. For their respiratory system they have openings called spiracles on the abdomen and thorax through which air enters and waste gases are expelled.

Metamorphosis

Many species of insects go through a series of changes called metamorphosis. Most insects (butterflies, beetles, ants, bees, moths, flies…) develop through complete metamorphosis. There are four stages of development:

• Egg• Larva• Pupa• Adult

Incomplete Metamorphosis

Grasshoppers, silverfish, lice, and crickets develop through incomplete metamorphosis. The three stages of development are egg, nymph (a small adult without wings), and adult.

Kingdom- AnimaliaPhylum- Arthropoda

Class- Arachnida

Arachnids

Arachnids are arthropods with only two body regions (the cephalothorax and abdomen). They have four pairs of legs but no antennae. Arachnids have 8 legs and poison glands, stingers, or fangs. Some arachnids are:

• Spiders• Scorpions• Mites• Ticks

Kingdom- AnimaliaPhylum- Arthropoda

Class- Chilopoda/Diplopoda

Centipedes & Millipedes

Centipedes have one pair of jointed legs per segment. Millipedes have two per segment. Centipedes have a pair of poison claws to inject venom into their prey (they eat snails, slugs, and worms). Millipedes feed on plants.

Kingdom- AnimaliaPhylum- Arthropoda

Class- Crustacea

CrustaceansCrustaceans are arthropods that have one or two antennae and jaws called mandibles for crushing food. They have five pairs of legs. The claws are for catching and holding food. The other four pairs are walking legs. Some members of the class Crustacea are:

• Crabs• Crayfish• Lobsters• Shrimp• Barnacles• Pill bugs • Water fleas

Blue CrabsA male crab, or "Jimmy", has a long narrow, inverted "T" shaped abdomen and has blue tipped claws.

A female crab can be easily identified by the shape of her abdomen.

Abdomen of immature female crabAbdomen of mature female crab

“Jimmy”

Some watermen say that a male blue crab looks like it has the Washington Monument on his belly!

“Sally”

An immature female, called "she-crab" or "Sally," has an inverted "V" (or triangular) shaped abdomen.

“Sook”

An adult female, called a "sook," has an inverted "U" (dome) shaped abdomen. Some watermen say that a sook has the U.S. Capitol Building on her belly! Another easy way to tell a male from a female is that all female crabs "paint their fingernails" (have red tipped claws)- males do not.

Pesticides and InsectsMost insects are harmless, but farmers who are concerned about crop yields often use pesticides (chemicals that kill undesirable plants and insects).

For Pesticide Use

• Farmers can produce more food

• New ways of applying pesticides may reduce amount needed and ensure it affects only the insect pests

Against Pesticide Use

• Kill not only intended pest but other organisms as well• Pesticides accumulate in body tissues of organisms• Environmental impact is too great

Kingdom- AnimaliaPhylum- Echinodermata

Echinoderms

Echinoderms are spiny skinned invertebrates that live on the ocean bottom. They include:

• Sea stars• Brittle stars• Sea urchins• Sand dollars • Sea cucumbers

Water-Vascular System

Sea stars have a water-vascular system (a network of water-filled canals) which attach to thousands of tube feet (‘suction cups’ that help the sea star feed/move).

Sea Stars

The sea star turns its stomach inside out and pushes it through its mouth to eat. It then secretes enzymes that digest the animal. When the meal is over, the sea star pulls its stomach back in.

The Sea Cucumber

This sea cucumber is eviscerating a portion of its intestines to thwart an attack.

Sea cucumbers have soft-bodies and tentacles around their mouth. When threatened sea cucumbers may expel their internal organs and simply regenerate them in a few weeks!

Importance of Echinoderms

• Providing information about how body parts regenerate• Feed on dead organisms in the marine environment

Echinoderms Similar to Chordates

Of invertebrates- most similar to chordates (mammals, birds, reptiles, amphibians, and fish)– Complex body systems– Embryo develops similar to chordates