Echinoderms and Mollusks

Invertebrates 2: Porifera, Cnidarians, Echinoderms,

and Mollusks

Section 27-4 Phylum Mollusca

• Over 80,000 different species of mollusks

• 2nd largest phylum in the animal kingdom.

Mollusk

• Soft bodies covered with a mantle.• Most also have shells.• Gills are specialized organs for getting

oxygen from water.• Most mollusks move with a muscular foot.

Section 27-4

Shell

Mantle cavity

Foot

Gills

Digestive tract

Snail

Earlymollusk

Clam

Squid

The Mollusk Body Plan

• One-part shells, including snails. These mollusks are gastropods or univalves.

• Two-part shelled mollusks are bivalves include clams and oysters.

• Cephalopods, includes the octopus and squid, do not have external shells. They also have tentacles to swim and catch prey.

Section 27-4Three Kinds of Mollusks

The Unknowns• Caudofoveata: shell-less wormlike live in burrows on the deep-sea floor. • Aplacophorans: lack a shell live in the depths of the ocean• Monoplacopharans: caplike shell, less than 3 cm long • found in the deep ocean.• Polyplacophorans(chitons): Flat long shell w/ 8 plates. Live on rocky shorelines and graze on plants.• Scaphopods(tusk shells): Long tube-shaped shell tapered at one end with both

ends open. Burrow into the sand.

Class Gastropoda• Stomach-footed mollusks, or gastropods,

have broad flat foot on the bottom surface of their bodies.

• Snails and slugs are gastropods.

• They use the foot for moving from place to place.

Interesting GastropodsNudibranchs – No Shell (Slugs)

Sea hare – Defense System

Class Bivalvia• They have a wedge or hatchet-shaped

foot and two shells .• Include clams, muscles, oysters, and

scallops. • Use the hatchet-foot to burrow into the soft sand and mud.

Interesting Bivalves

Giant Clam Scallops – Free Swimming

Class Cephalopoda

• The foot of these forms tentacles, or arms, which are located on the animal’s head circling its mouth

• Tentacles have suckers that can attach to prey.

• Tentacles are used for capturing prey, to crawl and also to cling to rocks.

Cephalopods (continued)• Generally good swimmers, especially

squid, which are the fastest-swimming invertebrates.

• A squid swims by forcing a jet of water from between its mantle and body through a tube.

• Cephalopods have larger, better-developed brains than other invertebrates.

• Includes octopus and squid.

Extinct Cephalopods

• AMMONOIDEA (Also called ammonites or ammonoids)

• Extensive Fossil Record

Interesting CephalopodsBlue-Ringed Octopus – Very small but deadly

Cuttlefish – Changes color

Nautilus

•Deep Sea Swimmer

•Only Cephalopod with a full shell

Comparing the Three Major Groups of Mollusks

MOLLUSK GROUPGastropods

Bivalves

Cephalopods

SHELLShell-less orsingle-shelled

Two shells held together by oneor two muscles

Internal shell orno shell

FOOTMuscular foot located on ventral side and used for movement

Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot.

Head is attached to a single foot. The foot is divided into tentacles or arms.

EXAMPLESSnail, slug, sea hare, nudibranch

Clam, oyster, mussel, scallop

Octopus, squid, cuttlefish, nautilus

Section 27-4Compare/Contrast Table

Echinoderms

Sea StarsSand DollarSea Urchins

Sea Cucumbers

Echinoderms

• Name echinoderm means “spiny skin.”• The bodies of most echinoderms can be

divided into five parts, like wagon wheels with five spokes. = Radial Symmetry

Water Vascular System• Have a water vascular system

of tubes, or canals, inside and outside of their bodies.

• In canals the water is forced, under pressure, into structures called tube feet.

• Tube feet are used to crawl over the bottom of the ocean floor.

Digestive system• Some echinoderms, such

as starfish, can grip objects tightly enough with their tube feet and arms to pry open clam shells.

• Then they move their “reversible”

stomach into the clam to digest its soft tissues.

Section 28-1Section 28-4

Eyespot

Endoskeletal plates

AnusStomach

Madreporite

Reproductive glands

Tube footSucker

Ring canalRadial canal

Digestive glands

The Anatomy of a Starfish

Some Examples are….

Sea Urchins and Sand Dollars• Parts of the skeleton are

fused to form a bony shell.

• Have spines that pass through holes in the shell.

• The spines work with the tubefeet to help the animal crawl.

• Some spines have tiny pinchers on their ends for defense or feeding.

Sea Cucumbers• They are long and rounded and have short

tentacles around the mouths.• They lie on the sea floor, crawling slowly

over the ocean bottom or burrowing in soft mud or sand.

Sea Cucumber expelling intestines in defense mode

SEA APPLE