TSW identify and describe the basic characteristics of mollusks

What is a mollusk? Soft-bodied animal with an internal or an external shell Very diverse phylum, but all share similar developmental stages Many have TROCHOPHORE larvae: free-swimming larval stage of aquatic mollusks

Form & Function True COELOMS surrounded by mesoderm tissue Complex, interrelated organ system

Body Plan 4 Main Parts FOOT: Muscular, used for crawling, burrowing, & capturing prey MANTLE: Thin layer of tissue covering the mollusk’s body like a cloak SHELL: Made of calcium carbonate; has been lost in some groups VISCERAL MASS: Internal organs

Feeding Can be herbivores, carnivores, filter feeders, detritivores, or parasites

Feeding Structures RADULA: Flexible, tongue-like structure to which hundreds of tiny teeth are attached SIPHON: Tubelike structure through which water enters and leaves the body

Respiration Aquatic mollusks typically breathe using gills inside their mantle cavity

Circulation Oxygen & nutrients are carried to all parts of a mollusk’s body via an open or closed circulatory system OPEN: Blood is pumped through vessels by a simple heart sinuses gills  heart Works best in slow-moving mollusks (snails & clams) b/c their demand for oxygen is low

Excretion Cells release nitrogen-containing waste into the blood in the form of ammonia Nephridia: tubular structures that collect fluids from the coelom and exchange salts and other substances with body tissues as the fluid passes along the tubules for excretion.

Response Complexity varies depending on the species

Movement Rippling motion of the foot (snails) Jet propulsion (octopi)

Reproduction Sexually via external fertilization Some have internal fertilization Some are hermaphrodites

Groups of Mollusks Divided into three main groups depending on the characteristics of the foot and shell Gastropoda Bivalvia Cephalopoda

Gastropoda Gastropods Shell-less or single-shelled Move using a muscular foot on the ventral side Examples: Pond snails, sea butterflies, sea hares, limpets, & nudibranchs

Bivalvia Bivalves 2 shells that are held together by 1 or 2 powerful muscles Most stay in one lace much of the time Many are filter feeders, but some use long, muscular extensions to collect food

Bivalve: Examples Clams, oysters, mussels, and scallops

Cephalopoda Cephalopods Soft-bodied, head is attached to a singular foot that is divided into tentacles or arms Most active of all mollusks Small internal shell or no shell at all Numerous, complex sense organs

Cephalopods: Examples Octopi, squid, cuttlefish, nautilus