Subquadrate Cyclinella Shell, Cyclinella subquadrata

Subquadrate Cyclinella Shell, Cyclinella subquadrata. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2025. Size: 4.1 cm (1.6 inches) x 3.9 cm (1.5 inches) x 1.2 cm (0.5 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Subquadrate Cyclinella Shell, Cyclinella subquadrata. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2025. Size: 4.1 cm (1.6 inches) x 4.1 cm (1.6 inches) x 1.2 cm (0.5 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny: The Subquadrate Cyclinella, Cyclinella subquadrata (Hanley, 1845), is a bivalve mollusk that is a member of the Veneridae Family of Venus Clam Shells and the Dosiniinae subfamily. The Cyclinella genus is one of two genera in the Dosiniinae subfamily, and there are four species in the Cyclinella genus. They are known in Mexico as as the Almeja Subcuadrada.

Morphology: Subquadrate Cyclinella Shells vary in outline from round to ovate. They are moderately inflated in profile. The beaks are also moderately inflated. These shells are sculpted with fine commarginal striae. The exterior is cream colored with a translucent to tan periostracum. The interior is generally white to cream in color but sometimes the exterior color shows through. Subquadrate Cyclinella Shells reach a maximum of around 8.1 cm (3.1 inches), though some sources extend the maximum length to 9.5 cm (3.7 inches).

Habitat and Distribution: Subquadrate Cyclinella Shells are found in mud and sand substrates. They live in the intertidal zone, and to depths of 75 m (246 feet). They are a subtropical to tropical Eastern Pacific species.  Subquadrate Cyclinella Shells are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Isla Cedros, Baja California, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior: Subquadrate Cyclinella Shells  are suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are prey for shore birds, crabs, fish, sea stars, and predatory mollusks. Subquadrate Cyclinella Shells are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formally documented. From a conservation perspective they have not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: Artemis macilenta, Artemis subquadrata, Arthemis saccata, Cyclinella galera, Cyclinella kroeyeri, Cyclinella kroeyeri ulloana, Venus (Artemis) kroeyeri, and Venus kroeyeri.