Zoology Rainier Jr/Sr High School Mr. Taylor Phylum Mollusca Zoology Rainier Jr/Sr High School Mr. Taylor

Mollusks Kingdom Animalia Mollusca means “soft body” Phylum Mollusca Live in a variety of habitats; marine, freshwater, and land species.

Mollusca characteristics Bilateral symmetry Have a true coelom Body plan: 3 parts Head/foot: mouth, sensory organs, motor organs. Visceral mass: digestive, excretory, respiratory, circulatory, and reproductive organs Mantle: surrounds visceral mass & secretes the shell (if present)

Mollusca characteristics Shells: mollusks have zero, one, or two shells Shell is made of protein and often hardened by calcium carbonate. The shell can be internal or external. Radula: all mollusks except bivalves have a rasping tongue called a radula

Class Bivalvia The “classic” bivalves are clams, oysters, and scallops Bivalves have 2 external shells no distinct head region no radula few sensory organs

Clams Have typical bivalve anatomy Possess a few light and touch sensors on edge of shells Circulatory system is open and utilizes a 3 chamber heart Clams have separate sexes

Clams Have an incurrent and excurrent siphon Incurrent siphon pulls water into the clam’s shell and over the gills: O2 and CO2 exchange Gills are covered with mucus and traps food particles as water flows over the gills. Cilia move food to mouth then on to stomach, intestines, and out anus.

Clams

Scallops Scallops have “eyes” along the edge of their shells Non-visual photosensors Can detect movement by sensing light and dark passing from one sensor to another. Scallops move by forcefully closing their shells and ejecting water.

Scallops

Oysters Oysters are the sessile bivalves. As with other mollusks, the larval stage is a free-swimming trochophore and serves as a dispersal mechanism.

Class Gastropoda Gastropoda means “belly foot” This class is where we find snails and slugs. One shell Snails have an external shell Some slugs have an internal shell

Snails Bilateral symmetry, but many are coiled. Have a nerve system with 6 ganglia. Photosensors on “eyestalks” detect light and shadows. Have an open circulatory system. Sexual reproduction with internal fertilization.

Snails Respire using gills. Land-based snails must keep them moist: limits territory. See text page 661 to see where the gills are located under their shell. Movement by using cilia on bottom of foot Secrete mucus to glide on Provides protection of foot Gives traction so snails can climb smooth, vertical surfaces

Snails

Slugs and Nudibranchs Slugs have either no shell (most) or an internal shell (only a few) Live in moist environments as they need to keep their skin moist to allow for respiration. Nudibranchs are special sea slugs They have no shells, gills, or mantle Have decorative plumes on their backs that increase skin surface area to allow for gas exchange.

Slugs and Nudibranchs

Class Cephalopoda Cephalopoda means “head foot” Octopus, squid, nautilus, and cuttlefish Characteristics include Very well-developed head and tentacles Shell Nautilus has an external shell Cuttlefish and squid have an internal shell Octopus have no shell

Class Cephalopoda Characteristics include Closed circulatory system Well-developed nervous system with a complex brain! Have jaws with a radula and beak All are predators!

Octopus Jet propelled using an excurrent siphon They have no shell and are extremely agile Large eyes are image forming. Suckers on tentacles not only grasp but have chemosensors and tactile (touch) sensors to locate prey. Sexes are separate and females will brood eggs (she cares for them and keeps predators away) Have the ability to change colors (camouflage)

Octopus

Squid Very similar to octopus with 2 more, but less-developed, tentacles. Not as agile Have an internal shell Giant squid in excess of 20 feet long have been found. As do octopus and cuttlefish, squid use “ink” as a defense mechanism

Squid

Nautilus Have an external shell with chambers Secretes shell as it grows, chambers become progressively larger. Live in outermost chamber. Uses shell for buoyancy: deep ocean by day, comes to shallow depths to feed at night.

Nautilus

Cuttlefish Ink has been used as a paint pigment for centuries.