Acanthina spirata (Blainville, 1832)

Common name(s): Angled unicorn, angular unicorn

Phylum Mollusca
 Class Gastropoda
   Subclass Prosobranchia
    Order Neogastropoda
      Suborder Rachiglossa
       Family Nucellidae
Acanthina spirata, about 3 cm long.  At San Simeon, CA
(Photo by: Dave Cowles, 1995)
Description:  This predatory intertidal snail does not have a hairy periostracum.  Its aperture has a siphonal notch but not an anal notch (picture).  It has a horny operculum and distinct spiral ridges but no axial ridges.  The spiral ridges are dark gray, brown, or greenish and often make a checkered pattern.  The corners of the whorls are angled with a prominent shoulder.  The columella has no folds (picture).  Has a sharp tooth on the outer lip of the aperture (picture).  Shell is up to 4 cm long.

How to Distinguish from Similar Species: This species looks similar to Nucella species, especially N. ostrina, but no Nucella species has the tooth on the outer lip of the aperture.  In California, may be confused with A. spirata but can be distinguished by the prominent shoulder and the strong spiral sculpture.

Geographical Range: Washington to Baja California. Uncommon north of California.

Depth Range:_

Habitat: Rocky intertidal.

Biology/Natural History: A predatory snail.  Prey includes Littorina, barnacles.  Egg capsules are 4-9 mm long.  Some only develop to the gastrula stage, while some continue development and eat these "nurse eggs".  There are 17 to 46 embryos per capsule.  Hatch as juveniles. Crepidula adunca are sometimes found on this snail, though Crepidula prefers the black turban snail.

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Dichotomous Keys:
Kozloff 1987, 1996
Smith and Carlton, 1975

General References:
Kozloff, 1993
Niesen, 1994

Scientific Articles:

General Notes and Observations:  Locations, abundances, unusual behaviors:

The aperture of Acanthina spirata has a distinctive tooth on the outer lip.  Note the operculum and smooth columella.  Photo by Dave Cowles, San Simeon, CA, 1995

Authors and Editors of Page:
Dave Cowles (2005):  Created original page