Nassarius fossatus (Gould, 1850)

Common name(s): Channeled basket whelk, Channeled nassa, Channeled dog whelk, Basket shell, Giant western nassa

Synonyms:  Nassa fossatus, Alectrion fossatus
Phylum Mollusca
 Class Gastropoda
  Subclass Prosobranchia
   Order Neogastropoda
    Suborder Rachiglossa
    Family Nassariidae
Nassarius fossatus shell (contains a hermit crab) found intertidally near Rosario.  Note the deep groove at the anterior (right) end that separates the anterior end of the body whorl from the rest of the shell.
(Photo by: Dave Cowles July 2006)
Description:  As with all members of family Nassariidae, the coiled shell has a well-developed spire and a siphonal notch or canal but no anal notch (though this species has a narrow posterior notch near where the anal notch would be found) (photo).  The outer shell is not highly polished and is usually sculptured.  The widest part of the aperture is less than half the diameter of the shell.  Has a horny operculum.  The lowermost portion of the body whorl, including the siphonal canal, is set off from the rest of the shell by a deep groove for most species in the family (photo).  Nassarius fossatus has the deep groove (photo) and has both axial ribs and spiral ridges, though the axial ribs do not extend as far anteriorly as the anterior groove on the body whorl (the axial ribs cover only about 1/3 of the body whorl).  The spire is acute.  The outer lip of the aperture is finely toothed at the margin and ridged inside (photo).  The inner lip of the aperture has a broad callus on the columella, usually orange, that spreads out over the body whorl and extends well posterior to the anterior end of the outer lip (photo).  The siphonal canal is short and wide (photo).  Besides the anterior siphonal canal, the aperture also has a narrow notch at the posterior end (photo).  Usually gray-brown to ash colored shell, with the callus on the columella often orange.  Height to 4.5 cm (which is one of the largest species in this genus), with about 7 whorls.

How to Distinguish from Similar Species:  Ilyanassa obsoleta and Searlesia dira do not have the deep anterior groove.  Nassarius fraterculus has spiral ridges only on the body whorl.  Several other species have axial ribs which reach to the angerior groove.  Of these, N. mendicus has much more pronounced axial ribs than spiral ridges, while N. rhinites and N. perpinguis have small axial ribs and spiral ridges which intersect to form distinct beads (may need magnification to see).

Geographical Range:  Vancouver Island, B.C. to Laguna San Ignacio, Baja California.  This is the most common carnivorous snail on mud flats along the US west coast.  It is most common in the northern parts of its range.

Depth Range:  Low intertidal to 18 m

Habitat:  Intertidal and more commonly subtidal on sandy areas and mud flats.

Biology/Natural History:  Feeds as a predator or primarily a scavenger.  Can crawl well on rock, or on top of or just below the surface of sand or mud.  They crawl with both sides of the large foot, leaving a distinctive track in the sand.  Attracted from long distances by rotting meat, which it can smell with its long proboscis.  It can crawl rapidly.  When feeding, it wraps its foot completely around the food until it is consumed.  May also drill in clams or snails.  Predators include the seastar Pisaster brevispinus.  When contacted by P. brevispinus, N. fossatus may writhe so violently with its foot that it twists into somersaults and even vaults into the water column.  At other times it may simply turn and crawl swiftly away, rocking its shell back and forth.   Sometimes the colonial hydroid Clytia bakeri, which is one of few hydroids that grow on exposed sandy shores, is found growing on shells of this species.  Deposits its egg capsules on eelgrass or other firm objects in mud flats in late winter and spring.  A typical string of eggs may be 6 cm long and contain 45 eggs.  The individual capsules are about 3 mm long.  They are laid overlapping one another to produce a "shingled" appearance.

The wicker-basketlike appearance of the intersecting radial ribs and spiral ridges is the reason this species is called a basket whelk.

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Dichotomous Keys:
  Griffith, 1967
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
  Brusca and Brusca, 1978
  Harbo, 1997
  Hinton, 1987
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris, 1966
  Morris et al., 1980
  Niesen, 1994
  Niesen, 1997
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

Web sites:

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

The outer margin of the aperture has small teeth on the margin and is ridged inside.  It has a short siphonal notch or canal at the anterior end (right above) and a small notch at the posterior end.
The innr margin and columella have alarge callus which is usually orange.
This shell has a hermit crab inside.

Another, smaller individual

This anterior view of the shell clearly shows the groove which sets off the anterior end from the rest of the shell.

Authors and Editors of Page:
Dave Cowles (2006):  Created original page