Irregular Spindle Shell, Callifusus irregularis

Irregular Spindle Shell, Callifusus irregularis. Shell collected off the beach at Punta Chivato, Baja California Sur, April, 2025. Size: 10.3 cm (4.0 inches) x 2.8 cm (1.1 inches). Photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Phylogeny: The Irregular Spindle Shell, Callifusus irregularis (Grabau, 1904) is a gastropod member of the  Fasciolaridae Family of Spindle, Horse Conchs and Tulip Shells. The genus Callifusus is one of sixty-eight genera in this family, and there are two species in this genus. They are known in Mexico as Eje Irregular.

Description: Irregular Spindle Shells have a spindle-shaped outline and they consist of around eight whorls. The exterior is sculpted with coarse spiral lines and vertical ridges, which form knobs on the whorls. They have a high spire and a very long, open, anterior canal. The canal is sinuous. Irregular Spindle Shells are white, with some specimens showing purple tinge inside the outer lip and the tip of the canal. These shells reach a maximum of 23.5 cm (9.2 inches) in length, although most specimens are much smaller.

Habitat and Distribution: Irregular Spindle Shells are found on sandy substrates within the subtidal zone at depthts between 22 m (72 feet ) and 50 m (165 feet). They are a subtropical to tropical Eastern Pacific species that are found in Mexican waters of the Pacific  Ocean from Cedros Island, Baja California to the southern tip of the Baja Peninsula. Within the Sea of Cortez they are found from Punta Chivato, Baja California Sur to Cabo San Lucas, Baja California Sur.

Ecology and Behavior:  Irregular Spindle Shells are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Other species in Family Fasciolariidae are predatory carnivores that feed on mollusks, worms, and barnacles. They are gonochoric and reproduce sexually, with internal fertilization. The eggs are laid in protective capsules. There is no mention in the available literature of this species engaging in any types of parasitic, commensal, or symbiotic relationships. From a conservation perspective they have not been formally evaluated.

Synonyms:  Fusinus irregularis, Fusus dupetitthouarsi var. irregularis, and Fusus irregularis.