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
notch would be found) (photo).
shell is not highly polished and is usually sculptured. The
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
species in the family (photo).
fossatus has the deep groove (photo)
has both axial
ribs and spiral
ridges, though the axial
ribs do not extend as far anteriorly as the anterior groove
ribs cover only about 1/3 of the body
whorl). The spire
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
to the anterior end of the outer lip (photo).
canal is short and wide (photo).
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
in this genus), with about 7 whorls.
Nassarius fossatus (Gould, 1850)
Common name(s): Channeled basket
whelk, Channeled nassa,
Channeled dog whelk, Basket shell, Giant western nassa
Nassa fossatus, Alectrion
|Nassarius fossatus shell (contains a
hermit crab) found intertidally
near Rosario. Note the deep groove at the anterior (right)
separates the anterior end of the body whorl from the rest of the shell.
|(Photo by: Dave Cowles
How to Distinguish from
Ilyanassa obsoleta and Searlesia
dira do not have the deep anterior
groove. Nassarius fraterculus
has spiral ridges only on the body whorl. Several other
axial ribs which reach to the angerior groove. Of these, N.
has much more pronounced axial ribs than spiral ridges, while N.
and N. perpinguis have small axial ribs and spiral
intersect to form distinct beads (may need magnification to see).
B.C. to Laguna San Ignacio, Baja California. This is the most
carnivorous snail on mud flats along the US west coast. It is
common in the northern parts of its range.
Low intertidal to 18
Intertidal and more commonly
subtidal on sandy areas and mud flats.
a predator or primarily a scavenger. Can crawl well on rock,
top of or just below the surface of sand or mud. They crawl
both sides of the large foot, leaving a distinctive track in the
Attracted from long distances by rotting meat, which it can smell with
its long proboscis. It can crawl rapidly. When
wraps its foot completely around the food until it is
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
At other times it may simply turn and crawl swiftly away, rocking its
back and forth. Sometimes the colonial hydroid
which is one of few hydroids that grow on exposed sandy shores, is
growing on shells of this species. Deposits its egg capsules
or other firm objects in mud flats in late winter and spring.
string of eggs may be 6 cm long and contain 45 eggs. The
capsules are about 3 mm long. They are laid overlapping one
to produce a "shingled" appearance.
The wicker-basketlike appearance of the intersecting radial
spiral ridges is the reason this species is called a basket whelk.
and Carlton, 1975
and Brusca, 1978
and McConnaughey, 1985
et al., 1980
et al., 1985
General Notes and
Observations: Locations, abundances,
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
end (right above) and a small notch at the posterior end.
The innr margin and columella have alarge callus which is usually
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