Echinoderms and Mollusks Invertebrates 2: Porifera, Cnidarians, Echinoderms, and Mollusks

Phylum Mollusca Over 80,000 different species of mollusks Section 27-4 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.

The Mollusk Body Plan Section 27-4 Squid Snail Shell Mantle cavity Foot Gills Digestive tract Clam Early mollusk

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 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 Scallops – Free Swimming Giant Clam

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

Compare/Contrast Table Section 27-4 Comparing the Three Major Groups of Mollusks MOLLUSK GROUP Gastropods Bivalves Cephalopods SHELL Shell-less or single-shelled Two shells held together by one or two muscles Internal shell or no 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. EXAMPLES Snail, slug, sea hare, nudibranch Clam, oyster, mussel, scallop Octopus, squid, cuttlefish, nautilus

Sea Stars Sand Dollar Sea Urchins Sea Cucumbers 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.

The Anatomy of a Starfish Section 28-1 Section 28-4 Eyespot Endoskeletal plates Anus Stomach Madreporite Reproductive glands Tube foot Sucker Ring canal Radial canal Digestive glands 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 