Short Thracia Shell, Thracia curta

Short Thracia Shell, Thracia curta. Shell collected off the beach of Punta Chivato, Baja California Sur, January 2026. Size: 4.3 cm (1.7 inches) x 3.2 cm (1.3 inches) x 1.2 cm (0.5 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny: The Short Thracia Shell Thracia curta Conrad, 1837, is a bivalve mollusk in the Thraciidae Family of Lantern Shells. The genus Thracia is one of seventeen genera in this family, and there are forty-four species in this genus. Both the name Thraciidae and the genus name Thracia come from the Greek words referring to the ancient region of Thrace, where  shells from this family were found. The species name curta comes from the Latin adjective meaning “short” or “incomplete”. In Mexico, this species is called Thracia Corta.

Description: Short Thracia Shells may be ovate to trigonal in outline, and are inflated in profile. They vary in shape depending on the shape of the area where they nest. The shells are of thick construction and the right valve is usually more inflated than the left. The anterior end is rounded. The posterior is longer than the anterior, and truncate (appearing chopped-off). The posterior end is set off from the rest of the shell by a radial ridge. Depending on the nesting site, the ventral margin may be sinuous. These shells are sculpted with commarginal growth lines. The pallial sinus is short and wide. The hinge has a projecting resilifer. These shells are generally whitish, though some have a greenish interior. Short Thracia Shells reach a maximum length of around 5.3 cm (2.1 inches).

Habitat and Distribution: Short Thracia Shells are found nestled in rock crevasses and empty Pholad (piddock shells) holes. They live from the intertidal zone to depths of 48 m (157 feet). They are a temperate to tropical Eastern Pacific species. They are found along the entire Pacific coast of Mexico, including the entire Gulf of California.

Ecology and Behavior: Short Thracia Shells are suspension feeders that filter plankton and fine detritus from the surrounding water. In turn they are preyed upon by birds, crabs, carnivorous mollusks and rays. Their reproductive behavior is poorly documented. Species in this family may be gonochoric (male or female for life) or simultaneous hermaphrodites (having both male and female reproductive organs). They reproduce sexually, though some sources say fertilization is external, and others say internal. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formally documented.

Synonyms: Lepton clementinum, Mysella clementina, Thracia (Ixartia) curta, Thracia anconensis, Thracia quentinensis, and Ungulina luticola.