freshwater mussels & endangered fish Glossary
Unless otherwise noted, these definitions represent a compilation from those previously published by Burch (1975),Clarke (1981), Cummings and Mayer (1992), Howells et al. (1996), and Webster’s Ninth New Collegiate Dictionary (1990).
- anadromous—ascending rivers from the sea for breeding
- anterior end—the shorter end of the shell as measured from the umbo to the margin. In a live animal, the foot extends from this end, and this end is usually embedded in the substrate
- beak cavity—a cavity that extends into the beak, usually under the pseudocardinal teeth (Oesch 1995)
- biramous—having two branches
- bradytictic—species with females gravid for long periods, usually becoming gravid in late summer or early fall and remaining gravid through the spring or early summer
- branchial septa—a dividing membrane within the gills or associated structures
- demibranchs—one-half of one of the paired gills of a freshwater bivalve (Parmalee and Bogan 1998)
- dendritic—resembling a tree in structure
- dorsal margin—the margin of the shell with the umbo, hinge, and ligament
- endemic—restricted or peculiar to a locality or region
- elliptical—oval
- elongate—stretched out
- excurrent aperture—an opening of the mantle at the posterior end of the mussel which expels water, wastes, glochidia or sperm; may be tube-like; above incurrent aperture
- extant—in reference to a population, present as live individuals in a particular area
- extirpated—in reference to a population, no longer present as live individuals in a particular area
- fish host—a species of fish parasitized by the glochidia of a mussel species
- foot—a muscular part of the body used for movement on or within the substrate; extends from antero-ventral shell area
- glochidia—the parasitic life stage of a freshwater mussel
- gravid—condition when glochidia or young mussels are present in the gills
- growth rests—a ridge formed during an intermediate stage of growth when this area was the edge of the shell (Clarke 1981)
- hermaphroditic—an individual that has both male and female sexual organs (Clarke 1981).
- hinge line—the dorsal edge where the two valves of a shell meet; connected by the hinge ligament
- incurrent aperture—an opening of the mantle at the posterior end of the mussel which brings water and other resources into the body of the mussel; may be tube-like; below excurrent aperture
- interdental projection—a "tooth" that juts out from the interdentum
- interdentum—the area between the pseudocardinal and lateral teeth
iridescent—a play of colors producing rainbow effects (as in a soap bubble)
- lateral teeth—the long blade-like structures along the hinge line of each valve and closest to the posterior end of the shell
- left valve—the shell half on the left side when the hinge is facing up and the anterior end is directed forward (away from you)
- mantle—the folds or lobes of the body wall of a mollusk that lines the shell and bears shell-secreting glands; the number of lobes or folds varies by species.
marsupium—structures for enclosing or carrying eggs or young
- nacre—the inner surface of the shell
- obovate—ovate with the narrower end basal
- pallial line—a linear impression on the inner surface of the shell, parallel to the ventral margin, the line of attachment of the mantle muscles.
- papillae—small finger-like sensory projections associated with the outer margins of the apertures, and in some species, associated with the outer margins of the mantle.
- periostracum—the external surface of the shell
- plications—parallel ridges
- posterior end—the longer end of the shell as measured from the umbo to the margin. In a live animal, the siphons extend from this end.
- posterior ridge—a ridge along the external surface of the shell extending from the umbo to the posterio-ventral margin.
- pseudocardinal teeth—the compact, often triangular, tooth like structures along the hinge line of each valve and closest to the anterior end of the shell.
- rays—streaks or lines of color on the external surface of the shell.
- right valve—the right half of the shell when the hinge is facing up and the anterior end is directed forward (away from you)
- sexually dimorphic—a condition in which males and females of the same species are morphologically different, usually indicated in unionoids by an expanded posterior marsupial area in the female in contrast to a more pointed or bluntly rounded area in the male. (Parmalee and Bogan 1998)
- shell—the hard outer covering of the mussel.
- subovate—less than ovate
- suprabranchial chamber—the dorsal portion of the gills
- tachytictic—species with females gravid for short periods, usually late spring or early summer
- teeth—the structures along the hinge line on the inner surface of the shell that serve to lock the two valves together when the animal closes its shell.
- terminus—an extreme point or element
- trapezoidal—a four sided form having only two sides parallel
- umbo—the raised part at the dorsal margin of each valve, an external structure
- valves—one of the two halves of the shell
- vestigial—a structure that is less fully developed compared with closely related forms
- ventral margin—the bottom edge of the shell, opposite the hinge line