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 Gastropods
Nudibranchs – 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 Cephalopods
Blue-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 MollusksComparing the Three Major Groups of Mollusks
MOLLUSK GROUP
Gastropods
Bivalves
Cephalopods
MOLLUSK GROUP
Gastropods
Bivalves
Cephalopods
SHELL
Shell-less orsingle-shelled
Two shells held together by oneor two muscles
Internal shell orno shell
SHELL
Shell-less orsingle-shelled
Two shells held together by oneor two muscles
Internal shell orno shell
FOOT
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.
FOOT
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.
EXAMPLES
Snail, slug, sea hare, nudibranch
Clam, oyster, mussel, scallop
Octopus, squid, cuttlefish, nautilus
EXAMPLES
Snail, slug, sea hare, nudibranch
Clam, oyster, mussel, scallop
Octopus, squid, cuttlefish, nautilus
Section 27-4Compare/Contrast Table
Echinoderms
Sea Stars
Sand Dollar
Sea 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
Anus
Stomach
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