Dart Screw Shell, Turritella radula

Dart Screw Shell, Turritella radula. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, March 2015. Size: 8.2 cm (3.2 inches) x 1.7 cm (0.7 inches).

Phylogeny: The Dart Screw Shell, Turritella radula (Keiner, 1843), is a gastropod mollusk that is a member of the Turretellidae Family of Turret Shells. The genus Turritella is one of twenty-four genera in this family, and there are seventy-three species in this genus.

Description: The Dart Screw Shell has sixteen to twenty deeply convex whorls. There are two beaded ridges that follow along the whorls and finely beaded lines in between these ridges. The exterior of the shell is marbled with yellowish-brown, and darker brown and white. The interior is either brown or white with brown blotches. Dart Screw Shells reach a maximum of 10.0 cm (3.9 inches) in length and 2.1 cm (0.8 inches) in height.

Habitat and Distribution:  Dart Screw Shells are found on and within sand substrate at depths between 10 m (35 feet) and 150 m (500 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 Cedros Island, Baja California along the central and northwest coasts of the Baja Peninsula and north of La Paz, Baja California, in the Sea of Cortez.

Ecology and Behavior: Dart Screw Shells are suspension feeders, which use mucous sheets on their gills to capture organic particles from the water. In turn they are preyed upon by crabs, fish, and predatory mollusks. They are gonochoric and reproduce sexually, through broadcast spawning, with internal fertilization. The eggs are laid in protective capsules, attached to rocks. They are known to host several species of endoparasites, especially trematodes. There is no mention in the available literature of them engaging in any types of  commensal or symbiotic relationships. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Turritella mariana.