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Mussel Glossary

This glossary will introduce the special names of the specific parts of a mussel, and the scientific terms for the functions, processes, and activities associated with mussel anatomy and life cycle. There are several labeled drawings to assist users with mussel anatomy.

Glossary Sources:
Bogan, Arthur E. 2002. Workbook and key to the freshwater bivalves of North Carolina. North Carolina Freshwater Mussel Conservation Partnership, Raleigh.
Burch, John B. 1975. Freshwater unionacean clams (Mollusca: Pelecypoda) of North America. Malacological Publications, Hamburg, Michigan.

Cummings, Kevin S., and Christine A. Mayer. 1992. Field guide to freshwater mussels of the Midwest. Manual 5. Illinois Natural History Survey, Champaign.

adductor muscles (noun)

a pair of muscles that close the two valves of a mussel shell. Each muscle extends from the left valve to the right valve, one in the anterior part of the shell and the other in the posterior part.

anterior end (noun)

front end of a mussel where its foot protrudes and its beak is located.

beak (noun)

the raised portion of the dorsal margin of a shell, also called the umbo. The beak is the oldest portion of a mussel shell, formed when the animal was very young.

beak cavity (noun)

the depression or cavity on the inside of each valve beneath the beak.

beak sculpture (noun)

natural surface markings on the beak, consisting of raised loops, ridges, or bumps.

bivalve (noun)

a type of mollusk with a shell consisting of two valves (Class Bivalvia).

byssus threads (noun)

a bundle of tough threads secreted by a gland in the foot of the zebra mussel (Dreissena polymorpha) and some other bivalves, used to anchor it to a hard object. The glochidial larvae of some pond mussels (e.g., Anodonta suborbiculata) also possess long byssus threads, which form underwater "nets" or "webs" that probably aid the attachment of larvae to host fish.

chevron (noun)

a V-shaped marking.

compressed (adjective)

flattened or pressed together from side to side.

concentric (adjective)

having a common center, such as a series of ridges or loops radiating outward from the beak of a mussel shell.

distal (adjective)

situated away from a point of origin or attachment.

dorsal (adjective)

pertaining to the top or back of an animal; in mussels, the hinge area.

elliptical (adjective)

having the form of an ellipse (an elongated circle).

elongate (adjective)

having a long or extended shape.

exotic species (noun)

a species of foreign origin, not native to an area where it occurs. Asian clams (Corbicula fluminea) and zebra mussels (Dreissena polymorpha) are exotic species in North America that were introduced by humans in the 20th century.

extirpated (adjective)

a species that has become extinct within a portion of its range.

foot (noun)

a muscular organ that a mussel uses to anchor itself in the substrate or move from one place to another.

gills (noun)

platelike respiratory organs in freshwater mussels that also help gather food particles ("filter-feeding") and provide a place for female mussels to store their glochidial larvae (marsupium).

glochidia (noun)

bivalved larvae of freshwater mussels, which are generally parasitic on a fish host.

growth lines (noun)

concentric lines on the outside of a shell that indicate periods of arrested growth. Extended periods of growth arrest occur during winter, forming darker or thicker growth lines.

hinge (noun)

the dorsal part of a mussel shell where the left and right valves attach.

hinge ligament (noun)

an elastic structure that unites the two valves of a mussel along the top of the shell.

hinge teeth (noun)

interlocking triangular or ridge-like structures located along the hinge of some mussels, which serve to keep the valves in alignment (pseudocardinal and lateral teeth).

inflated (adjective)

swollen or expanded from side to side.

interdentum (noun)

the portion of the hinge between the pseudocardinal and lateral teeth.

iridescent (adjective)

displaying an array of colors like those of a rainbow.

labial palp (noun)

an appendage of soft tissue that channels food particles to the mouth.

larva (noun)

immature form of an animal that undergoes complete metamorphosis.

lateral teeth (noun)

elongated, interlocking ridge-like structures (hinge teeth) located along the hinge of some valves.

left valve (noun)

the left half of a mussel shell, which can be identified by orienting the shell with the hinge facing up and the anterior end forward (away from the observer).

mantle (noun)

soft tissue enclosing the body of a mussel, the principal function of which is to secrete the shell. In some species of the Subfamily Lampsilinae, the posterior portion of the female mantle serves to attract host fish by mimicking the shape and movement of fish or crayfish.

mollusk (noun)

an invertebrate animal belonging to the Phylum Mollusca. Mollusks typically have soft, unsegmented bodies wholly or partially enclosed by calcareous shells. Includes tusk shells, chitons, bivalves, snails, squids, and octopuses.

muscle scar (noun)

a pit or depression marking the attachment of a muscle to the inside of the shell. For example, the anterior adductor muscle scar is the point of attachment for the anterior adductor muscle.

nacre (noun)

the lustrous interior layer of mussel shell, which is composed of shingle-shaped crystals of calcium carbonate (CaCO3). Usually white, pink, salmon, or purple, and often iridescent. Also called the "mother-of-pearl" layer.

oblong (adjective)

having an elongated shape, which may be rectangular or elliptical.

ovate (adjective)

having the shape or outline of an egg; egg-shaped.

pallial line (noun)

a linear groove on the inside of a shell marking the line of attachment of the mantle to the shell.

periostracum (noun)

exterior organic layer of mussel shell, which may be yellow, green, brown, or black and is sometimes marked by green rays. The periostracum protects the calcareous layers of shell (nacre and prismatic) from dissolution by acids in water.

plications (noun)

parallel ridges or folds on the outer surface of a shell.

posterior end (noun)

rear end of a mussel where its inhalent and exhalent siphons are located.

posterior ridge (noun)

a ridge on the exterior of a mussel shell that extends from the beak to the posterior margin.

posterior slope (noun)

the area on the exterior of a valve extending from the posterior ridge to the dorsal margin.

prismatic layer (noun)

the middle layer of mussel shell, which is composed of column-shaped crystals of calcium carbonate (CaCO3).

pseudocardinal teeth (noun)

triangular, often serrated structures (hinge teeth) located near the anterior-dorsal margin of some valves.

pustule (noun)

a small bump or raised knob on the outer surface of a valve, also called a tubercle.

quadrate (adjective)

square, or nearly square, in outline.

ray (noun)

a linear color marking, usually green, which appears on the outer surface (periostracum) of some mussel species.

ridge (noun)

an elongate elevation on the outer surface of a valve. Multiple parallel ridges form plications or undulations.

right valve (noun)

the right half of a mussel shell, which can be identified by orienting the shell with the hinge facing up and the anterior end forward (away from the observer).

sculpture (noun)

raised natural surface markings on the outside of the shell, consisting of knobs, pustules, ridges, or spines.

serrated (adjective)

notched or grooved.

sexual dimorphism (noun)

a condition in which males and females of a species differ from one another in shape. Evident in some female mussels by an enlargement or extension of the posterior-ventral part of the shell.

shell margin (noun)

the outer edge or circumference of a valve when laid flat.

siltation (noun)

the deposition of silt (fine mud) on the bottom of a river or lake, which, in great amounts, may threaten mussel survival.

siphon (noun)

Opening on the posterior end of a mussel, formed by the mantle tissue, which allow for the circulation of water inside the animal. Water enters through the inhalent siphon and is expelled through the exhalent siphon.

solid (adjective)

thick or heavy shell.

spawn (verb)

in reproduction, the release of sperm or eggs in water.

striated (adjective)

marked with numerous parallel furrows or grooves.

sulcus (noun)

a shallow, elongate furrow or depression on the outer surface of a shell that generally extends from the beak to the posterior or ventral margin.

truncate (adjective)

having an end that appears to be shortened or squared off.

tubercle (noun)

a raised bump or projection on the outside of a shell, also called a pustule.

umbo (noun)

the raised portion of the dorsal margin of a shell, also called the beak.

valve (noun)

the right or left half of a bivalve shell.

ventral (adjective)

the lower or bottom edge of a shell.


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