Family Mytilidae

Shell size to 90 mm; shell mussel-shaped, ventral margin straight or slightly concave, posterior end rounded. Shell surface smooth except for fine growth lines. Hinge with one or two teeth. Periostracum flaky. Externally brown with green tinges usually concentrated around margins. Internally nacreous, whitish or light-purple. This species has been introduced to the East Coast of the USA, part of the Caribbean Sea, and the Gulf of Mexico from New Zealand.

Shell size to 9 mm; shell small for family, elongate-ovate, inflated, thin-walled, with taller section on posterior one third. Umbo poorly defined. Two slanted lines divide valve in three areas: a smooth central one, anterior and posterior areas with strong radial ribs. Color greenish-brown, but central area of lighter color. Inner nacreous layer very thin, translucent.

Shell size to 65 mm; shell similar to Modiolus americanus, but with umbones smaller and not swollen, and coarse, thick, brown periostracum with long filaments. Color brownish with oblique whitish ray on older specimens; umbones white.

Shell size to 100 mm; shell mussel-shaped, trigonal. Sculpture of fine growth lines. Umbones swollen, not terminal (away from end of shell). No hinge teeth. Periostracum heavy, sometimes hair-like. Color light-brown with blush of rose (concentrated on umbones) and purple streaks.

Shell size to 28 mm; shell small for family, elongate-ovate, inflated, thin-walled, with taller section on posterior one third. Hinge with slight expansion under umbo. Color brown, with very sharp, slanted line separating lighter color posterior end from darker anterior end. Nacreous bluish inside.

Shell size to 35 mm; shell elongate, cylindrical, tapering at posterior end, thin-walled. Two grooves run obliquely from the shell beak to the posterior (rear) area of each valve. The posterior half of each valve can be heavily encrusted with a relatively soft, calcium-carbonate deposit. This deposit projects backward, forming a spatula-like structure that reaches beyond the posterior end of each valve. A rock-boring species, found in calcium carbonate substrates such as live or dead coral and mollusk shells. The second photo shows a Mahogany Date Mussel boring into the top valve of a Jewel bBx. All specimens from the Museum collection, all collected on Sanibel.

Shell size to 50 mm; shell moderately inflated. Umbonal region strongly curved. Sculpture of numerous, fine radial lines. Color dark-grayish to dark-brown with interspaces between radial sculpture of lighter color. Internally purplish to rosy-brown with narrow light-blue or grayish edge. Living in protected bay areas.

Shell size to 20 mm; Shell inflated, with ridge on postero-dorsal part of shell bearing radiating lines. Shell margins finely serrated. Interior of shell iridescent, bluish-white. Periostracum thick, heavy, but often absent in dead shells. This is a coral-rock boring species, found locally within small coral heads. The common name is a misnomer, as these mussels do not eat coral, only use the coral skeleton as substrate for boring.

Shell size to 75 mm; Shell mussel-shaped, thin but strong. Sculpture of numerous bifurcating ribs. No hinge teeth. Color yellowish- to greenish-brown, inner surface bluish-white with posterior end (rounded area) flushed with purple. Species found on hard substrates in the back bay areas of Southwest Florida.

Shell size to 25 mm; shell mussel-shaped, trigonal, elongate. Sculpture of hundred or more fine ribs which form minute denticles on inner edge of valves. Color yellowish-brown to dark-brown, inner surface metallic-purple mottled with white.