Abductor muscle - A muscle that moves any part of the body away from the central
midline. In brachiopods, it opens the bivalve shell
Adaptive radiation - Evolution of a variety of different species from a single common
ancestor. Each is adapted for a particular niche, and the appearance of the
descendants may vary considerably from each other and the ancestor.
Adductor muscle - A muscle that moves part of the body toward the central midline. In
brachiopodsand bivalves, it closes the bivalve shell.
Albumen gland - The albumen gland is a compound tubular gland, the walls of the
tubules being composed of large apocrine gland cells with basal nuclei. These cells
contain numerous large ovoid granules, which stain a pale violet colour in
Atrium - each of the two upper cavities of the heart from which blood is passed to the
ventricles. The right atrium receives deoxygenated blood from the veins of the body; the
left atrium receives oxygenated blood from the pulmonary vein.
Bioluminescence - How living organisms produce light. Many organisms that live in the
deep, dark of the oceans, or in other environments at night, use flashing lights,
bioluminescence, to communicate
Branchial heart - Modification of the circulatory system to form secondary hearts that
pump blood into the gills
Cecum - pouch or large tubelike structure in the lower abdominal cavity that receives
undigested food material from the small intestine and is considered the first region of
the large intestine, absorb fluids and salts that remain after completion of intestinal
digestion and absorption and to mix its contents with a lubricating substance, mucus
Ciliated sorting field - Ciliary sorting fields are located between the stomach and
digestive gland where intracellular digestion of the food will occur. These sorting fields
allow only particles with the proper size to enter the digestive gland. Those larger than
this are either rejected and passed to the intestine or sent back into the stomach for
Ciliated ventral foot - The ventral foot is used in locomotion. This foot propels the
mollusc by utilizing muscular waves and/or cilia in combination with mucus,
Crystalline style - A rodlike structure in some mollusc stomachs made of enzymatic
proteins required for digestion. Cilia lining the stomach rotate the crystalline style, which
grinds against the gastric shield to release the digestive enzymes Ctenidia - Molluscan gills that often have additional functions other than respiration,
shaped like a comb or a feather, with a central part from which many filaments or plate-
like structures protrude, lined up in a row. It hangs into the mantle cavity and increases
the area available for gas exchange
Dart sac - an eversible appendage of the female reproductive organs in certain land snails, a sac connected
with the reproductive organs of land snails, which contains a dart, or arrowlike structure.
Digestive gland - Many invertebrates, including molluscs, arthropods, and echinoderms,
have pockets or evaginations from the main alimentary tract where specialized digestive
Elastic capsule chromatophore - Specialized pigmented cells on the surface of
cephalopods that, by changing their shape, expose differing amounts of pigment
changing the color and appearance of the cephalopod
Excurrent siphon - Incurrent and excurrent siphons refer to the way that clams take in
and release water. The clam takes in water the mantle cavity via an Incurrent siphon.
Excess water is released via the excurrent siphon.
Gastric shield - an organ in the digestive tract of bivalves and some gastropods against which
a crystalline style typically rotates, in an action resembling that of a mortar and pestle. The
gastric shield is permeated by microcanals which transmit digestive enzymes from the stomach,
and serves to protect the cells of the stomach lining from the abrasive effects of the style
Glochidia - Free-swimming, larval stage of some freshwater, bivalve molluscs. Glochidia are
brooded inside the gill chamber. After release, they parasitize fish until the glochidia's
development is complete.
Hectocotylus arm a modified arm of a male cephalopod that is specially and variously adapted to effect the
fertilization of the eggs, an arm that in argonauts and some octopods receives the spermatophores, is inserted into
the female mantle cavity, and then is broken free from the body of the male
Hermaphrodite duct a duct for the passage of both eggs and sperm in mollusks having an ovotestis
Hinge ligament A hinge ligament is an crucial part of the anatomical structure of a bivalve shell,
i.e. the shell of a bivalve mollusk. The shell of a bivalve has two valvesand these are joined
together by the ligament at the dorsal edge of the shell, the ligam