Update: 2004.11.17

Terminology

aculeate - having spines or prickles

acute - sharply angled

adductor muscles - posterior muscles which internally close the valves of the shell

adductor scar - impression on interior shell where adductor muscles attach

albino - white due to lack of colour pigments

angulate - angled, formed with corners

anterior - forward, front or head end (opposite of posterior)

antero- - combining form of anterior (e.g., anterodorsal)

antimarginal - sculpture more or less perpendicular to valve margin

aragonite - orthorhombic crystalline form of calcium carbonite

auricle(s) - ear-like projections on the anterior and posterior ends of the hinge line (also ears)

auricular crura - tubercles and ridges inside the auricles

bathymetric - pertaining to the measurement of depth of water

beak - projecting region above the hinge marking the earliest growth of the shell (see also umbo)

bifid - divided into two parts by a groove

bifurcate - divided into two, especially in sculpture

blotch - irregular dot of contrasting colour

bridged - partly covered

bulbous - globular

byssal fasciole - track left by developing byssal notch

byssal gape - opening remaining when the shell is closed for passage of the byssus

byssal notch - gap near anterior auricle on right valve for passage of the byssus

byssal sinus - embayment below anterior auricle on left valve corresponding to the byssal notch of the right valve

byssate - with a byssus

byssus - a bundle of fibers to anchor   to the substratum

calcareous - composed mostly of calcium carbonate

calcite - rhombohedral crystalline form of calcium carbonate

cancellate - having a pattern of intersecting radial and concentric ribs (see also reticulate)

cardinal - central part of the hinge area directly below the beaks

cardinal crura - narrow plate-like teeth radiating from the resilifer

cardinal teeth - teeth directly below and radiating from the umbo

carina - a prominent, sharp-edged or keel-like radial ridge on the surface of the shell

carinate - with a carinae

cementation - fixation to the substratum by shell secretion

cline - a geographically and gradually developing difference in appearance of certain populations of the same species

collar - a raised lip bordering a suture

commarginal - parallel to the ventral shell margin

commensal - living with another animal, a form of symbiosis

compressed - flattened

concave - curved or arched inwards

concentric - nearly commarginal, paralleling the ventral margin

conspecific - belonging to the same species

convex - inflated in left-right axis

corneus - horny in texture

corrugated - folded or ridged, broadly and haevily sculptured

costa (pl. costae) - a rib-like sculptural element

crenate (or crenulate) - with regular notches or corrugations

crura (singular, crus) - lamellar ridges on the hinge plate

ctenolium - row of small teeth on edge of byssal notch

cuneate - wedge-shaped

decussate - having a latticed surface formed by the intersection of fine ribs

demarcated - set off, as by a ridge, furrow or abrupt change in sculpture

denticle - low, rounded tooth

dentition - referring to the vertical hinge teeth

depressed - low in proportion to diameter

diameter - measure of shell convexity

disc (or disk) - central part of the external surface of the valve

dissoconch - post-larval shell

divaricate - antimarginal or diverging sculpture, often forming chevrons

dorsal - toward the hinge line

ears - lateral projections of the hinge line (see also auricles)

ecomorph - a morphology resulting from living in a particular place

elongate - extended, considerably longer in one dimension than another

epifaunally - living attached to the substratum

equilateral - anterior and posterior size of the shell nearly equal in size

equivalve - with valves equal in size and shape

extant      - not extinct

fascicle - a small bunch or radial ribs

flexuous - with a bend or curve in the shell

fold - a broad undulation

foliated layer - shell microstructure of lath-like calcitic crystals that form sheets like roof shingles

gape - opening left between valves when shell is closed

gibbous - swollen unevenly

globose - roughly spherical shape

granular - bearing granules as surface sculpture

granule - a pustular surface sculpture

growth striae - commarginal lines on the shell surface that mark growth intervals

height - the greatest dorsoventral dimension perpendicular to hinge line

heterodont - with distinct, differentiated cardinal and lateral teeth

hinge - collective term for structures of the dorsal region that function in opening and closing the valves

hinge line - antero-posterior axis of the hinge

hinge teeth - shelly structures fitting into sockets in the opposite valve and serving to assure accurate closure

hyaline - thin and nearly transparent

hypertrophied scales - inflated

imbricate - roof-like shingles overlapping sculpture

incremental lines - faint concentric growth lines

inequilateral - anterior and posterior sections of the valves dissimilar in shape and size

inequivalve - having the two valves dissimilar in shape and size

inflated - swollen or strongly convex

intercalary - between (e.g., smaller ribs between two major ribs)

intercostal - between ribs

interspaces - region between adjacent ribs

interstitial - channels between ribs

lamella (pl. lamellae) - thin, raised ridge(s) of external sculpture

lamellate - covered with scales

lamellose - with thin scales or plates

lamina (pl. laminae) - thin, raised ridge(s) of the hinge

left valve - upper valve

length - dimension along antero-posterior axis

lenticular - flattened and generally circular

ligament - elastic proteinaceous structure joining the two valves dorsally

ligamental pit - broad subumbonal depression accommodating a ligament

lira (pl. lirae) - a threadlike sculptural element

lirate - having a threadlike sculpture

longitudinal - direction of ribs or lines from hinge to ventral margin

maculations - spots, generally of irregular size, shape and distribution

margin - the edge, particularly of a shell surface

medial - central

monophyletic - with a single evolutionary origin

nacreous - shell microstructure of thin aragonite layers, characterized by iridescence

nestling - fixed in a crevice or crack

node - a small knob

nodose - sculpture of nodes or tubercles

oblique - intermediate between dorso-ventral and antero-posterior direction

obsolete - sculpture that disappear or remain undeveloped

ocelli - minute, simple eyes

opisthogyrate form - with beaks pointed backwards, or posteriorly

orbicular - circular in outline

ovate or ovoid - having an oval shape

pallial line - scar on valve interior from attachment of marginal pallial muscles

pellucid - transparent or translucent

plica - fold

plicae - folds

plicate - folded or twisted lengthwise

polyphyletic - with more than one unrelated origin

posterior - towards the back end (opposite of anterior)

postero- - combining form of posterior

prismatic - shell microstructure consisting of calcitic or aragonitic prisms

prodissoconch - the shell secreted by the larva, preserved at the tip of the umbones

punctate - surface with minute pits

pustule - knobby sculpture, generally smaller than a tubercle

radial - radiating in relatively unbroken lines from the umbones to the ventral margin

resilifer - a structure that supports the internal ligament

resilium (pl. resilia) - internal portion of the ligament

reticulate - external sculpture of a network of intersecting elements

rib - an elongated radial or concentric structural element

riblet - a narrow rib

right valve - lower valve

rostrate - pointed or beaked

scabrous - rough, scaly

scale - a localized projection of shell sculpture

sculpture - relief pattern on the shell exterior

serrate - a saw-like margin

sessile - attached to some substrate, not free to move

shagreen - net-like or honeycomb-like exterior sculpture

spine - long calcareous projecting sculpture

spinose - having spines or thornlike protuberances

squamose - sculpture of small scales

stria (pl. striae) - minute linear sculpture, indication a growth stage

striate - marked with a sculpture of fine scratches, grooves, or lines

sub- - combining form meaning nearly (e.g., suborbicular)

substratum (pl. substrata) - bottom sediment

symbiotic - two dissimilar organisms living in intimate or close association

thread - narrow rib

trigonal - triangular in outline

truncate - sharply or squarely cut off

tubercle - a small knob or lump

umbo (pl. umbones) - the upper part of a valve as seen from the outside

undulated - waved

variant - a shell differing slightly in form or colour from other   shells of the same species

variegated - with patches of different colours

ventral margin - the lower margin, opposite to the hinge line

ventricose - strongly inflated or swollen

width - the antero-posterior dimension of the shell

xenomorphic - assumption in form and sculpture of the substratum

 

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