Mollusca & Echinodermata – Key Vocabulary

Vocabulary flashcards highlighting essential terms and definitions for the phyla Mollusca and Echinodermata.

Radula

Chitinous, tongue-like scraping or drilling organ found in most mollusks (absent in bivalves).

Mantle

Membranous or muscular covering that surrounds the visceral mass and often secretes the shell in mollusks.

Mantle Cavity

Space between mantle and visceral mass; houses gills, anus, and excretory openings.

Trochophore Larva

Free-swimming, ciliated larval stage shared by mollusks and annelids.

Muscular Foot

Strong ventral structure in mollusks used for locomotion; modified into tentacles in cephalopods.

Visceral Mass

Soft-bodied region of a mollusk containing internal organs such as digestive, excretory, and reproductive systems.

Calcium Carbonate Shell

External exoskeleton secreted by the mantle in many mollusks for protection and support.

Open Circulatory System

Circulatory arrangement where blood flows through sinuses instead of vessels; typical of most mollusks.

Closed Circulatory System

Blood remains in vessels; characteristic of cephalopods among mollusks.

Nephridia

Primitive kidney-like organs in mollusks that remove nitrogenous wastes such as ammonia.

Dioecious

Having separate male and female individuals; common in mollusks and echinoderms.

External Fertilization

Gametes are released into the water for fertilization; used by bivalves and many marine gastropods.

Internal Fertilization

Sperm deposited inside the female body; occurs in cephalopods and terrestrial gastropods.

Operculum (Gastropods)

Lid-like structure attached to the foot that seals the shell opening when the animal withdraws.

Bivalvia

Mollusk class with two-part hinged shells (clams, mussels, oysters, scallops).

Gastropoda

Mollusk class that includes snails, slugs, limpets; generally possess a single shell or none.

Cephalopoda

Fast-moving, tentacled mollusks (octopus, squid, cuttlefish, nautilus) with well-developed brains and closed circulation.

Camouflage (Cephalopods)

Ability to rapidly change skin color and texture for concealment or communication.

Ink Cloud

Dark fluid released by cephalopods as a defense mechanism.

Protostome

Developmental pattern in which the mouth forms from the embryonic blastopore; mollusks are protostomes.

Coelomate

Animal possessing a true body cavity completely lined by mesoderm; both mollusks and echinoderms are coelomates.

Pentaradial Symmetry

Five-part radial body plan seen in adult echinoderms (e.g., sea stars).

Deuterostome

Developmental pattern where the blastopore becomes the anus; echinoderms are deuterostomes.

Endoskeleton (Echinoderms)

Internal skeleton of calcium carbonate plates providing support and protection.

Water Vascular System

Hydraulic network in echinoderms used for locomotion, feeding, and gas exchange.

Madreporite

Porous, sieve-like plate through which water enters an echinoderm’s water vascular system.

Tube Feet

Fluid-filled, suction-cup appendages connected to the water vascular system for movement and respiration.

Class Asteroidea

Echinoderm class containing sea stars; usually predatory with five arms and tube feet.

Class Ophiuroidea

Echinoderm class of brittle stars; slender flexible arms, often filter feeders or scavengers.

Class Echinoidea

Echinoderm class including sea urchins and sand dollars; spiny, typically herbivorous or detritivorous.

Class Holothuroidea

Echinoderm class consisting of sea cucumbers; elongated bodies, detritus feeders.

Cardiac Stomach

First stomach of sea stars that can be everted outside the body to digest prey externally.

Pyloric Stomach

Second stomach in sea stars that completes digestion before passing food to the intestine.

Skin Gills (Echinoderms)

Tiny projections on the body surface that aid in gas exchange and waste removal by diffusion.

Statocyst

Sensory organ in some echinoderms that detects body orientation relative to gravity.

Eyespot (Sea Stars)

Light-sensitive structure at the tip of each arm enabling basic vision.

Open vs. Closed Sinuses

In mollusks, blood flows through open sinuses except in cephalopods which maintain closed vessels.