Waxy Pacific Thracia Shell, Cyathodonta undulata

Waxy Pacific Thracia Shell, Cyathodonta undulata. Shell collected off the beach of Punta Chivato, Baja California Sur, April 2025. Size: 4.8 cm (1.9 inches) x 3.4 cm (1.3 inches) x 1.0 cm (0.4 inches). Collection, photograph and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Waxy Pacific Thracia Shell, Cyathodonta undulata, Resilifer. A key to the identification. Photograph and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny: The Waxy Pacific Thracia Shell, Cyathodonta undulata, Conrad, 1849 is a bivalve mollusk in the Thraciidae Family of Lantern Shells. The Cyathodonta Genus is one of seventeen genera in the Thraciidae Family, and there are eight species in the Cyathodonta Genus.

Description: Waxy Pacific Thracia Shells are ovate in outline and inflated in profile. The right valve is more convex than the left. These shells are thin and brittle. The anterior end is longer and rounded. The posterior is truncate (appearing cut off) and offset by a radial ridge. Waxy Pacific Thracia Shells are sculpted with commarginal undulations and fine radial pustules.  Interiorly, they have a projecting resilifer (process where internal ligament attaches at the hinge). These shells a white in color with a thin, tan, periostracum, which is most obvious at the posterior end. Waxy Pacific Thracia Shells reach a maximum of 5.0 cm (2.0 inches) in length.

Habitat and Distribution: Waxy Pacific Thracia Shells are found buried in sand, from the intertidal zone to depths of 64 m (210 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Magdalena Bay, Baja California Sur, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior: Waxy Pacific Thracia Shells are a poorly researched and documented species. Little is known about their behavior. Other species in this family are suspension feeders that filter plankton and fine detritus from the surrounding water. Again, for other species in this family, their predators include shorebirds, crabs, carnivorous mollusks, and rays. 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.

Conservation: From a conservation perspective the Waxy Pacific Thracia has not been formally evaluated.

Synonyms: Cyathodonta lucasana and Cyathodonta undulata peruviana.