American horse mussel

Modiolus americanus

Family Mytilidae - mussels, true

Bivalve (2 shells); shell thin, oblong, moderately inflated, wider at the posterior end than anterior end, shell widest in the center, beak just behind anterior end, lower margin slightly concave; color reddish brown to brown, may have slight purplish tinge; inside smooth, glossy with pink to purple color on ventral half, dorsal half bluish white; prominent oblique hump or ridge from beak to posterior margin, sometimes with whitish streak beneath keel; fine concentric growth rings; depression from beak to widest part of shell on ventral margin.
Similar Species
Similar to the chestnut mussel but more narrow at anterior end.
Gulf, sandy-shelly bottoms, may attach to coral
Maximum Size
12.7 cm (5 in)
Other Common Names
Atlantic ribbed mussel, tulip mussel
Previous Scientific Names
Modiolus tulipa