Page 266 - The Freshwater Mussels of Oklahoma

GLOSSARY

Anterior end: the shorter end of the shell (from the umbo), the end of the shell usually embedded in the
substrate
Anterior wing: extension of the shell above the hinge area anterior to the umbo
Beak: (= Umbo): raised or inflated area on the dorsal part of the shell that represents the early growth
region
Beak cavity (= Umbo cavity): depression or pocket on the inside of the shell within the beak (umbo)
Dorsal: the part of the shell with the umbo and hinge ligament
Epidermis (= Periostracum): outside surface layer of the mussel shell
Excurrent siphon (= excurrent aperture): dorsal opening where mantles join posteriorly where water is
expelled from the mantle cavity, often characterized by a thickening of the mantle edge and may
have associated papillae and/or pigment
Fluting: series of parallel, undulating ridges on the shell surface
Foot: muscular structure that can be protruded from the ventral part of the valves and used for locomotion
Gills: pairs of tissue flaps within the mantle cavity, there are two on each side of the body, and responsible
for gas exchange, food entrapment and as a brooding pouch for developing young
Hinge: the dorsal region of the shell where the left and right valves are connected
Hinge plate: the dorsal region of the shell where the left and right valves connect, includes both
pseudocardinal and lateral teeth
Incurrent siphon (= incurrent aperture): ventral opening where mantles join posteriorly where water is
brought into the mantle cavity, often characterized by a thickening of the mantle edge and may
have associated papillae and/or pigment
Interdentum: the flat area of the hinge plate between the pseudocardinal and lateral teeth
Labial palps: flaps of ciliated tissue within the mantle cavity at the posterior end that deliver food ladened
mucous into the mouth
Lateral teeth: the elongated ridges (lamellae) extending toward the posterior part of the hinge area, allow
interlocking between the left and right valves
Left valve: the shell on the left when both shells are together with the dorsal portion upward and the
anterior end forward
Ligament (hinge ligament): the tough, flexible connection in the hinge (dorsal) area of the shell that
connects the left and right valves
Mantle: thin membranous structure that wraps the soft structures of the mussel and lines the shell
Mantle cavity: the area enclosed by the two membranous mantles, encloses the soft anatomy of the
mussel
Marsupium: a part of the gills where young are contained during early development
Marsupial swelling: expanded posterior/ventral region of the female shells of some mussel species
Mother of pearl(=nacre): the inner layer of shell, often white or iridescent, may be tinted with a variety
of colors
Muscle scar: rough or depressed area on the internal surface of the shell where muscles attach
Nacre (= Mother of Pearl): the inner layer of shell, often white or iridescent, may be tinted with a variety
of colors
Nodule: a bump, protuberance or knob on the external surface of the shell, generally larger than pustules
and are not usually as abundant as pustules
Pallial line: a line that is parallel to the ventral margin of the shell where the mantle attaches, usually
marked with a visible line or groove
Periostracum (= Epidermis): outside surface layer of the mussel shell
Posterior end: the longer end of the shell (from the umbo), the end of the shell usually protruding from
the substrate
Posterior ridge: a ridge extending from the umbo toward the posterior end of the shell
Posterior slope: the region of the shell between the dorsal margin and the posterior ridge
Posterior wing: extension of the shell above the hinge area posterior to the umbo
Pseudocardinal teeth: any of several projections on the anterior hinge area, the pseudocardinal teeth of
the left and right valves interlock
Pustule: small bump or protuberance on the external surface of the shell, often multiple pustules are

265