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Echinoderms and Mollusks. Invertebrates 2: Porifera , Cnidarians, Echinoderms, and Mollusks. Phylum Mollusca. Section 27-4. Over 80,000 different species of mollusks 2 nd largest phylum in the animal kingdom . . Mollusk. Soft bodies covered with a mantle.

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echinoderms and mollusks

Echinoderms and Mollusks

Invertebrates 2: Porifera, Cnidarians, Echinoderms, and Mollusks

phylum mollusca
Phylum Mollusca

Section 27-4

  • Over 80,000 different species of mollusks
  • 2nd largest phylum in the animal kingdom.
  • 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.
the mollusk body plan
The Mollusk Body Plan

Section 27-4




Mantle cavity



Digestive tract



three kinds of mollusks
Three Kinds of Mollusks

Section 27-4

  • 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.
the unknowns
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
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 gastropods
Interesting Gastropods

Nudibranchs – No Shell (Slugs)

Sea hare – Defense System

class bivalvia
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
Interesting Bivalves

Giant Clam

Scallops – Free Swimming

class cephalopoda
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
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
Extinct Cephalopods
  • AMMONOIDEA (Also called ammonites or ammonoids)
  • Extensive Fossil Record
interesting cephalopods
Interesting Cephalopods

Blue-Ringed Octopus – Very small but deadly

Cuttlefish – Changes color

  • Deep Sea Swimmer
  • Only Cephalopod with a full shell
compare contrast table
Compare/Contrast Table

Section 27-4

Comparing the Three Major Groups of Mollusks






Shell-less orsingle-shelled

Two shells held together by oneor two muscles

Internal shell orno shell


Muscular 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.


Snail, slug, sea hare, nudibranch

Clam, oyster, mussel, scallop

Octopus, squid, cuttlefish, nautilus



Sea Stars

Sand Dollar

Sea Urchins

Sea Cucumbers

  • 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
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
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




Endoskeletal plates



Digestive glands

Ring canal

Radial canal


Reproductive glands

Tube foot


The Anatomy of a Starfish

Section 28-1

Section 28-4

Some Examples are….

sea urchins and sand dollars
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
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.