Calliostoma annulatum 

Common name(s):  Ringed top snail, Purple-ringed top snail

Phylum Mollusca
 Class Gastropoda
   Subclass Prosobranchia
    Order Archaegastropoda
     Suborder Trochina
      Family Trochidae
Calliostoma annulatum collected by Dave Cowles, summer 2002.  Unknown location near Rosario.  Approximate height/width:  2 cm
(Photo by: Dave Cowles)
Description:  A top shell with a pearly interior, no nodes on columella, umbilicus closed, spiral ridges are beaded and brown on a cream or yellow background.  Most anterior spiral ridge on each whorl is violet or purple.  The apex is also usually purple (a purple band is also made near the columella).  Base of body whorl is nearly flat.  The whorls are only slightly inflated, and the sutures between whorls are not deeply indented.  Animal is pinkish orange with brown dorsal spots.  Shell is up to about 2-3 cm diameter/height, and usually has 8 flattened whorls.  The shell colors fade after the animal dies.

How to Distinguish from Similar Species: C. variegatum also has beaded spiral ridges but they are all tan or brown and the animal is cream (not orange) with brown spots.  C. ligatum has unbeaded spiral ridges and the animal is orange.

Geographical Range:  Forester Island, Alaska to Isla San Geronimo, Baja California

Depth Range:  Almost never intertidal.  More common on the open coast than in the Sound/Straits, although it is abundant subtidally in some areas of the San Juan Islands.

Habitat:  Seaweeds in shallow water.  Lives higher on kelp than does C. ligatum but below C. canaliculatum in CA.

Biology/Natural History:  This species (along with C. ligatum and C. canaliculatum) were collected by Captain James Cook and were among the first mollusk species on the US Pacific Coast to be named.  May climb up kelp stalk toward surface in bright weather--can climb 20-30 feet in a day.  Feeds on the kelp itself, or on encrusting diatoms, bryozoans, and hydroids.  Will also eat detritus and copepods, even may scavenge dead fish or other sea creatures.  May attack anemones or nudibranchs.  Apparently have "lips" or "jaws" which serve to cut up prey.  Mucus is secreted on the shell, which may help deter predation.

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Dichotomous Keys:

Kozloff, 1987
Smith and Carlton, 1975

General References:
Morris et al., 1980
Flora and Fairbanks, 1966
Kozloff 1993

Scientific Articles:

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

Underwater photo by Aaron Baldwin.

Authors and Editors of Page:
Dave Cowles (2002):  Created original page