BIOL 3610U: Comparative Zoology - Phylum Mollusca Part 1

Vocabulary practice flashcards covering anatomical features, shell layers, organ systems, and developmental stages of Phylum Mollusca based on Comparative Zoology Lecture 6.

Phylum Mollusca

The second-largest animal phylum after Arthropoda, comprising over $90,000$ living and $70,000$ fossil species of soft-bodied, bilaterally symmetrical, coelomate lophotrochozoans.

Head-foot

The anterior molluscan body region containing feeding, sensory, and locomotor organs that functions primarily through muscular action.

Visceral mass

The internal molluscan body region that contains the digestive, circulatory, excretory, and reproductive organs.

Mantle

A fold of tissue extending from the visceral mass that covers the soft body and secretes the calcium carbonate shell.

Mantle cavity

The space between the mantle and the visceral mass that typically houses the gills (ctenidia) and receives digestive, excretory, and reproductive products.

Radula

A rasping, protrusible, tongue-like organ found in most molluscs (absent in bivalves and solenogastres) that bears up to $250,000$ teeth and moves food into the digestive tract.

Odontophore

The cartilaginous supporting structure over which the molluscan radula lies and is moved back and forth by muscles.

Ctenidium

The specialized molluscan gill located inside the mantle cavity, composed of ciliated leaf-like filaments that serve as the site of respiratory gas exchange.

Countercurrent exchange

A respiratory flow arrangement where blood and water move in opposite directions across gill filaments to maintain a concentration gradient and maximize oxygen uptake.

Open circulatory system

A circulatory system found in most molluscs where hemolymph is pumped by the heart through vessels into blood sinuses to bathe body tissues directly.

Closed circulatory system

A circulatory network found in cephalopods where blood remains confined within vessels and capillaries to support their high metabolic demands.

Periostracum

The outer organic layer of the mollusc shell that protects the underlying calcareous layers.

Prismatic layer

The middle layer of the mollusc shell composed of calcium carbonate crystals embedded within a protein matrix.

Nacreous layer

The innermost iridescent shell layer (mother-of-pearl) situated next to the mantle, which continuously secretes nacre so the shell thickens throughout life.

Pearl

A calcareous structure formed when an irritant lodges within mantle tissue, prompting the mantle to deposit concentric layers of nacre around it.

Metanephridia

The pair of molluscan excretory organs (kidneys) consisting of tubules open at both ends to drain coelomic fluid and excrete waste.

Nephrostome

The ciliated funnel of a molluscan metanephridium that opens directly into the coelom.

Nephridiopore

The external opening of a molluscan metanephridium that discharges excretory waste into the mantle cavity.

Trochophore larva

The ancestral, free-swimming ciliated larval stage of lophotrochozoan protostomes characterized by an apical tuft of cilia and a prototroch band of cilia.

Veliger larva

A free-swimming molluscan larval stage following the trochophore, featuring ciliated velar lobes for swimming and feeding, an early foot, and a developing shell.

Molluscan coelom

A greatly reduced body cavity in molluscs that is limited primarily to the spaces surrounding the heart, gonads, and excretory organs.

Class Gastropoda

A major class of molluscs comprising snails, slugs, and limpets, typically featuring a broad crawling foot, cephalic sensory tentacles, and often a univalve shell.

Class Bivalvia

A major class of molluscs comprising clams, oysters, mussels, and scallops, characterized by a laterally compressed body, two hinged shell valves, a burrowing foot, and the absence of a radula.

Class Cephalopoda

A major class of marine molluscs comprising squids, octopuses, cuttlefish, and nautiluses, characterized by a closed circulatory system and a foot modified into arms, tentacles, and a funnel.