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Hipponix cranioides Carpenter, 1864
Common names
Flat Hoofsnail, Hoofsnail, Horse's hoofsnail, Hoof shell.
Synonyms
Antisabia cranioides, Have been incorrectly called Hipponix antiquatus, an Atlantic species.
Taxonomy
Phylum: Mollusca
Class: Gastropoda
Subclass: Prosobranchia
Order: Mesogastropoda
Suborder: Taenioglossa
Family: Hipponicidae
Description
This limpetlike snail family, called hoof snails is distinctive because it has an apex well behind the center of the shell so it looks somewhat like a horse hoof. In life, the foot attaches to rocks by a calcified platform. The shell is white, often with some brown periostracum. Shell sculpture is primarily of concentric rings. The apex is low. Diameter to 2.5 cm. Often overgrown with algae and encrusting organisms.
How to Distinguish from Similar Species
This is the only local native species of gastropod that has the apex well behind the center of the shell. Another member of this family, Sabia conica, from the Western Pacific, is found locally as an introduced species in British Columbia. Farther south and on Table Island north of Vancouver Island, Hipponix tumens, which has strong radial ridges, a periostracum of fine hairs, and the apex overhangs the posterior margin can be found. H. tumens grows to 1.5 cm diameter.
Geographical Range
Vancouver Island to Baja California (perhaps to Panama or Peru); most common in California.
Depth Range
Intertidal and shallow subtidal.
Habitat
On rocks on the open coast, occasionally attached to other shells. Often found in the burrows of piddock clams.
Biology/Natural History
Sessile as adults. The foot secretes a calcareous base on the rock and adheres to it like a "ventral valve". The shell fits tightly to the margins of the base so the animal can close tightly. Individuals of this species are often found in aggregations. Commonly found on the underside of overhangs or in crevices, especially in areas of heavy surf or subtidally. Easily overlooked. Males in a cluster tend to be smaller than females, so the species may be a protandric hermaphrodite. Females brood their eggs under the shell, and brooding females seem to be present year-round. The young hatch as creeping juveniles. The species feeds by extending a long, movable proboscis and dragging back fragments of detritus and coralline algae.
Scientific Articles
Reitzel, AM; Miner, BG; and McEdward, LR, 2004. Relationships between spawning date and larval development time for benthic marine invertebrates: a modeling approach. Marine Ecology Progress Series 280: 13-23
Sagarin, Raphael D., James P. Barry, Sarah E. Gilman, and Charles H. Baxter, 1999. Climate-Related Change in an Intertidal Community over Short and Long Time Scales. Ecological Monographs 69(4): 465-490
Valentine, James W., 1980. Camalu: A Pleistocene Terrace Fauna from Baja California. Journal of Paleontology 54(6): 1310-1318
Hipponix cranioides shell from Hobuck Beach on open coast. (Photos by: Dave Cowles, July 2007)
Hipponix cranioides anterior view.
Hipponix cranioides distribution.