Ilyanassa obsoleta (family Nassariidae) is probably the commonest
mollusk of muddy shores in the New England area (It also ranges north
and south of New England, but my observations are mainly in New
England).  You won't normally find a specimen in rocky areas or on
sandy beaches, but in most shallow muddy areas they are present by
the tens of thousands at least.  On some muddy shores at low tide the
density of exposed individuals exceeds 500 per square meter of beach.
One has to wonder how such a dense population can find sufficient
food.  Last spring, in one tidal inlet, I found an area of several
square meters that was absolutely blanketed with immature Ilyanassa
obsoleta (measuring about 5 to 8 mm).  You couldn't find a square
inch of uncovered bottom sediment among them.  In some places they
were piled several individuals deep. Just out of curiosity, I used a
pecten shell to cut out an area of one square inch (estimated),
scooped up the snails in that area, and counted them - there were79
individuals.  Extrapolating from that figure, I estimated there were
well over a million snails within a few meters of where I was
standing.  I could not see a single adult snail among this mass of
juveniles.
Ilyanassa obsoleta, like most members of its family, are scavengers,
feeding on detritus and especially on any dead animal tissue they can
find.  When the beach is covered with water, most of the snails burrow
into the mud and remain there until the next low tide.  However, a
bivalve with a broken shell, or a dead crab or fish will bring them
out of hiding in a hurry.  Such a food item, placed on the mud in an
area with no snails visible will often be completely covered with
snails within 15 minutes.  They have a keen sense of smell which
guides them quickly to available food.
Juveniles of this species have a sharp apex and a fine reticulated
sculpture, but the adults almost always have eroded spires, obscured
sculpture, heavy growth lines, and are generally pretty rough looking
and unattractive.
If the high school student who is working on this project needs any
specimens, I'll be glad to send him some.
Paul M.
Rhode Island, USA