Size
Shell length: reaching 25cm (10") Shell width: reaching: 10cm (4")
Recognition Characters
Has 10-15 radiating ribs, upper ribs are large and usually bear many erect, hollow, and sometimes tubular spines. Internal abductor muscle scar is completely surrounded by nacreous layer on inside of the shell.
Color
Dark, grayish brown
Habitat & Depth
Low tide line to 90'.
Distribution at GRNMS
Occasional. Bivalve remains only partially exposed above sediment with shell open. More common on soft sediments away from ledge.
Geographic Range
North Carolina south to Florida, Gulf of Mexico west to Texas and Brazil
Behavior & Notes
Atrina rigida and A. seminuda are very similar in morpholigical appearance. The two species are separated by the difference in the position of the posterior abductor muscle scar in the nacreous layer (the pearly interior region) of these bivalves. In A. rigida the scar reaches the edge or border of the nacreous layer while in A. seminuda the scar is completely enclosed within the nacreous layer.
Synonyms
Rehder 1981, Abbott and Dance 2000