Pacific Fly-speck Cerith Shell

Pacific Fly-speck Cerith Shell, Cerithium sterimuscarum. Shell collected off a beach in the greater Los Cabos area, Baja California Sur, May 2005. Size: 3.0 cm (1.2 inches) x 1.5 cm (0.6 inches). Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Pacific Fly-speck Cerith Shell, Cerithium stercusmuscarum Valenciennes, 1833, is a gastropod mollusk that is a member of the Cerithiidae Family of Cerith Shells. The genus Cerithium is one of  forty-seven genera in this family, and there are seventy-six species in this genus. They are also known as the Fly Dung Cerithium, the Fly Dung Whelk, and the Pacific Fly-specked Sand Snail and in Mexico as Cerithium Estiércol de la Mosca. The name Stercusmuscarum comes from Latin and means Fly dung, referring to the tiny specks on the shell.

Description: The Pacific Fly-speck Cerith Shell is a stout and solidly built shell that consist of six to eight whorls.  A row of pointed knobs separate the whorls, though sometimes these knobs are minimal. The oval-shaped aperture and the siphon canal are fairly small. The exterior color of the shell may be blue-gray, charcoal, or brown, with fine white speckles. The apex is often white. The interior is white or bluish though the rim of the outer lip is often darker colored and the bottom of the inside edge of the aperture (columella) is often white.  Pacific Fly-speck Cerith Shells reach a maximum height of 3.5 cm (1.4 inches) and 1.7 cm (0.7 inches) in height.

Habitat and Distribution: Pacific Fly-speck Cerith Shells are found on sand flats and within sand and mud substrates, often within estuaries within the intertidal zone, and to depths up to 6 m (20 feet). They are a subtropical to tropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean from Magdalena Bay, Baja California Sur south to Guatemala. They are found throughout the Sea of Cortez.

Ecology and Behavior:  Pacific Fly-speck Cerith Shells are  herbivores that feed primarily on micro algae and occasionally detritus. They are gonochoric and reproduce indirectly with the male transferring a spermatophore packet to the entrance of the mantle cavity of the female. The eggs are laid as a gelatinous mass. They are known to host marine flatworms of the genus paraprostatum in what appears to be a commensal relationship. 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: Cerithium (Vertagus) stercusmuscarum, Cerithium (Vertagus) stercusmuscarum var. minor, Cerithium callisoma, Cerithium muscarum pacei, Cerithium muscarum var. protracta, Cerithium notatum, and Thericium chara.