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 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.

Shell size to 40 mm; shell very thin, fragile, elongate, tapering gradually toward posterior end. Sculpture of fine concentric growth lines. Surface glossy. Hinge with no teeth. Ligament thin, small. Periostracum thin, green. Color light-gray. Inner surface nacreous. Found in mud in protected bay areas.