Mollusc Glossary

Adductor muscle
Muscle(s) in bivalves attached to both shells (valves); adductor muscles pull the two shells together (closes the shells). An elastic hinge pushes the shells apart (opens the shells).

Bivalve
A mollusc with two valves, or shells, joined together by a hinge. Members of Class Bivalvia ("two valves") can be found in freshwater and marine environments. Examples include clams, scallops, oysters, and mussels.

Byssal thread
A mass of strong, silky filaments by which certain bivalve mollusks, such as mussels, attach themselves to rocks and other fixed surfaces.

Cephalopod
A marine mollusc with a well-developed head surrounded by a ring of eight or more arms. Members of Class Cephalopoda ("head-footed") have a well-developed nervous system and propel themselves by jetting water through a siphon. They include pelagic and bottom dwellers. These animals maybe shell-less such as the octopus, possess an internal shell (squid and cuttlefish), or they may have an external shell (chambered nautilus).

Filter feeder
An animal that filters phytoplankton from the water for food. Most filter-feeding molluscs pump water across their gills, which act like fine-screen filters. A pair of siphons (inhalant and exhalent) allows burrowing bivalves to reach the water column without leaving the safety of their burrow.

Gastropod
A mollusc with well-developed foot, head, and body. Class Gastropoda ("stomach-footed") is the largest group of molluscs and can be found in terrestrial, freshwater, and marine habitats. Members of this group may be shell-less (slugs and sea hares), or typically possess a spiral-shaped shell (snails or conch).

Harvest areas
Regions where recreational fishing is allowed (open) or prohibited (closed) during certain times of the year.

Hermaphrodite
Having both female and male reproductive organs.

Introduced species
A non-native species that is deliberately introduced into an area or inadvertently brought into a region due to human activities.

Invasive species
An introduced species that threatens economic or environmental harm to ecosystems, habitats, or species. Only some introduced species become harmful.

Landing
The act of bringing an animal (fish, scallop, lobster, etc.) ashore.

Metapopulation
A population composed of smaller, isolated populations.

Non-native species
A species that is not indigenous, or naturally occurring, in a region.

Pediveliger
A specialized term for molluskan planktonic larvae. This stage follows the veliger stage and the foot is well developed.

Pelagic organism
An organism that lives in open water rather than on the bottom.

Protandric
Develops male reproductive organs initially and female reproductive organs at a later time.

Spat
Juvenile bivalve. Bivalves at this stage are often attached to other structures.

Spawning organism
An animal that reproduces by expelling eggs or sperm (or both eggs and sperm) into the surrounding water resulting in external fertilization.

Trochophore
A very early larval stage of molluscs (and some worms). The body is ringed by a band of cilia.

Veliger
A specialized term for molluscan planktonic larvae. Although they do not always have the same appearance as in adults, the shell and most organs can be seen.