A

Adductor muscle scars - where adductor muscles attach.

Ala - a wing-like extension of the dorsal shell margin.

Alate -having a wing.

Apustulose - without pustules.

B

Beak - the umbo.

Beak cavity - the inside of the beak.

Beak sculpture - patterns of ridges, loops, and bumps.

Biangular - with two angles.

C

Chevron - V- or arrowhead shaped.

Compressed - flattened or pressed together.

Concentric - circles, rings, or crescents.

Conglutinate - a cluster of few to many glochidia contained in a mucus matrix.

Corrugated - with ridges, wrinkles, or grooves.

Crenulate - with corrugated notches or wrinkles.

D

Demibranch - one gill of a pair of mussel gills.

Denticle - small tooth-like structures adjacent to the right pseudocardinal tooth.

Dimorphic - having two distinct forms.

Disk - the shell surface.

E

Ecophenotype - forms of a single species that are physically distinct in different environments.

Elliptical - ellipse shaped.

Elongate - long or extended.

Extant - still surviving.

Endemic - native only to a particular area.

Extinct - no longer surviving.

Extirpated - eliminated from a particular area.

F

Fecundity - the number of eggs, larvae, or both.

Fluted - grooves and ridges with a ruffle-like appearance.

G

Glochidium (glochidia - plural) - the larval stage of unionid and margaritiferid mussels prior to transformation to the juvenile stage.

Gravid - a female with eggs, embryos, or glochidia in her marsupia.

Growth-rest lines - alternating dark and light concentric lines in a mussel shell indicating periods of slow and fast growth, respectively. 

H

Hinge - the area where the right and left shelf halves articulate.

Hinge ligament - the elastic tissue that connects the right and left valves.

I

Inflated - swollen, expanded.

Interdentum - the area of the hinge between the lateral and pseudocardinal teeth.

Iridescent - a lustrous, pearly, or rainbow color appearance.

J

Juvenile - sexually immature.

K

Knob - a large pustule.

L

Lachrymose - drop-shaped.

Lamellar - thin and leaf- or blade-like.

Lateral teeth - elongate tooth structures along the hinge.

Lectotype - a primary type designated from the syntypic series subsequent to the original description.  

Ligulate - tongue-shaped.

Lotic - flowing water environments such as streams, springs, and rivers.

Lunule - a cavity or depression.

M

Mantle -  soft tissues surrounding the viscera.

Marsupial swelling - an inflated area of some female unionids to provide room for developing marsupia.

Marsupium - pouch-like structure on the gills where glochidia are held.

Muscle scars -  areas on the interior of the shell where muscles were attached.

N

Neotype - a primary type designated subsequent to its original description if no syntypes are available. 

Nacre - the inner layer of the shell, mother-of-pearl.

Nodular - with knobs or nodules.

O

Oblique - an axis not perpendicular to the base.

Oval (ovate) - egg shaped.

P

Periostracum - the outer shell layer, shell epidermis.

Plications - folds, ridges, particularly multiple ridges.

Posterior ridge - a ridge on the posterior half of the shell running from the beak to the margin.

Posterior slope - shell area between the posterior ridge and the dorso-posterior margin.

Pseudocardinal teeth - tooth-like structures located below the beak area.

Pustule - a bump or raised knob on the shell exterior.

Pyriform - pear shaped.

Q

Quadrate - square.

R

Radial - extending from a central area in a ray-like pattern.

Ray - colored lines on the shell exterior.

Reniform - kidney shaped.

Rib - a long, narrow strip or ridge.

Robust - stout, thick, more well-developed.

S

Sculpture - ridge, pustules on exterior of shell. 

Serrated - notched or grooved.

Shell margin - the exterior circumference edge of each valve.

Solid - hard, thick, not soft and chalky.

Striated - with fine lines or grooves.

Sulcus - a groove or long depression.

Syntype - one of a series of specimens used for an original series description when no holotype is designated; all have equal rank unless a a primary type (lectotype) is chose from among them, at which time the remainder become secondary types (paralectotypes). 

T

Type locality - the geographical place of capture, collection or observation of the name-bearing type.

Truncate - shortened or squared off.

U

Umbo - beak.

Umbonal cavity - the cavity inside the beak.

V

Valve - one half of a shell.

Vernacular name - common name; not the scientific name.

W

Wing - ala.