Ceratostoma foliatum (Gmelin, 1791)

Common Name: Leafy Hornmouth, Foliate hornmouth, Murex, Leafy thorn purpura, Foliated thorn purpura

Synonyms: Purpurata foliata, Pterorytis foliatus, Ceratostoma foliata
Phylum Mollusca
 Class Gastropoda
   Subclass Prosobranchia
    Order Neogastropoda
     Suborder Rachiglossa
      Family Muricidae
(Ceratostoma foliatum found on Northwest Island)
(Photo by Nathaniel Charbonneau July 27, 02)
Description:  Grows up to 10 cm high, but usually on more then 8 cm high, but usually no more then 8 cm high. The body whorl has three wide flanges or varices. Outer lip of aperture has a very strong protruding tooth near anterior end (picture); operculum is also horny (picture). The siphonal canal forms a closed tube and is bent backward (picture).  Coloring varies from gray, white (picture); to yellow-brown on body whorl, interior is white (picture). "In this species the juvenile shell is sculptured with numerous longitudinal ribs crossed at right angles by equally spaced spiral cords." As the shell increases the longitudinal ribs become channeled into groups that form projecting flanges called varices.  One of the varices ends on the closed siphonal canal and another ends on the previous canal, which is still visible but unused.  The body whorl is much larger than the whorls in the spire.  Length to 10 cm.

How to Distinguish from Similar Species:  Large Nucella lamellosa have a similar shape but do not have a closed siphonal canal, the tooth on the outer lip of the aperture, nor do the varices form into three large flanges as seen in this species.  In oyster beds, Ceratostoma inornatum, which has a duller shell ,may have more or less than 3 varices, and in which the spiral cords alternate large and small, may be found.  Ceratostoma nuttalli, which is found south of Piont Conception in California, is smaller, has nodules on the shell, has smaller varices, and has a single large axial rib between the varices.

Geographical Range:  Sitka (Alaska) to San Diego; uncommon south of Point Conception (CA)

Depth Range:  Low intertidal zone and subtidal to 60 m.

Habitat:  Found on rocky faces near barnacles and bivalves.  Avoids sand and mud.  Most common in areas of strong surf--is not found in protected waters in Alaska (but can commonly be found around Rosario)

Biology/Natural History:  Ceratostoma foliatum is a carnivorous snail that eats mainly barnacles such as Semibalanus cariosus and Balanus glandula, and bivalves such as Protothaca staminea, Mytilus californianus, and Mytilus trossulus.  It drills through their protective shell with its radula. After drilling through the shell Ceratostoma foliatum injects digestive enzymes into the prey's body cavity and sucks out the dissolved tissue. Sexes are separate and may form large groups during spring copulation.  After copulation, females lay their eggs in a communal mass nearby in stalked, yellow, flattened egg cases about 13 mm long, attached to rocks.  Each capsule has about 50 orange eggs and each female lays about 40 capsules per year.  Larval stages occur within the capsule, and the snails hatch as juveniles after 4-10 months.  Matures in about 4 years and can live 16 years.  Individuals older than this may have shells which have eroded so much at the apex that they are shorter than younger individuals (16-year olds may be only 5-6 cm long). 

Return to:
Main Page Alphabetic Index Systematic Index Glossary

Dichotomous Keys:
  Flora and Fairbanks (as Pterorytis foliatus)
  Griffith, 1967
  Kozloff, 1987, 1996
  Smith and Carlton, 1975

General References:
  Harbo, 1997
  Harbo, 1999
  Johnson and Snook, 1955 (As Purpura foliata)
  Kozloff, 1993
  Morris, 1966
  Morris et al., 1980
  Niesen, 1997
  O'Clair and O'Clair, 1998
  Rice, 1973
  Ricketts et al., 1985
  Sept, 1999
  White, 1976

Scientific Articles:

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

This view of the underside shows the horny operculum, the distinctive tooth on the outer lip of the aperture, and the closed siphonal canal.
Photo of a specimen from Coffin Rocks, Dave Cowles, July 2005

This white individual was found at Cape Flattery.

A striped individual, also from Cape Flattery.

The foot is a mottled cream color, as can be seen on this animal which is crawling along the aquarium wall.  Photo by Dave Cowles, July 2007

The varices on this species seem to have several functions.  According to a student project "Determination of functions of the varices on C. foliatum" by Mark Sauser and Deanna Berger at the Walla Walla College Marine Station in summer 2001, this species turns its shell so that the varices provide enhanced shading to the shell when in bright light.  Also, the varices cause the shell to land aperture downwards when dropped through water.  Shells from which the varices were removed most often landed aperture up.

Authors and Editors of Page:
Nathaniel Charbonneau (2002):  Created original page
Edited by:  Dave Cowles 8-2002, 2005, 2007
Edited by Hans Helmstetler 1-2003