8. THE PHYLUM MOLLUSCA
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becomes thickened, sometimes as wide as 1 cm, and with double or
triple lips.
Cole and Hancock are also of the opinion that: “ I n the most
severe cases, the constant irritation appears to interfere with the normal
metabolism of the oyster,” and may even lead to death. One cause of
death is the destruction of the adductor muscle resulting from the
gradual withdrawal of the mantle. When the mantle edge reaches the
muscle, the latter is almost completely covered by a horn-like ridge of
brownish deposited shell material and atrophies. Such destruction
naturally leads to gaping.
6. Odostomia tri$da Totten, 1834. (Figs. 186 and 187)
Fretter and Graham (1949) have listed Odostomia trijda as a
parasite of M y a arenaria.
Description. About 3-5 mm long ; shell pale greenish-white, conical,
with five or six whorls, each separated by a well-defined suture ; two
or three impressed lines below suture giving shell the appearance of
having multiple sutures; aperture oval; outer lip simple; inner lip
with a single oblique fold.
Ecology. This species is often found off of its host(s) under stones and
driftwood at low tide.
7. Other Pyramidellids
In addition to the six species given above, two others have been
reported associated with commercially important pelecypods. Cole
and Hancock (1955) have reported Chrysallida obtusa attached to
oysters, most probably Ostrea edulis, from Salcombe harbour, England,
and Verrill (1873) found a species referred to by him as Turbonilla
interrupta associated with ‘‘ Pecten and other shells ” in Vineyard
Sound, Massachusetts. Since the shells on which Verrill found T .
interrupta were empty, it cannot be definitely stated at this time whether
this gastropod was a parasite of the living animals.
285
becomes thickened, sometimes as wide as 1 cm, and with double or
triple lips.
Cole and Hancock are also of the opinion that: “ I n the most
severe cases, the constant irritation appears to interfere with the normal
metabolism of the oyster,” and may even lead to death. One cause of
death is the destruction of the adductor muscle resulting from the
gradual withdrawal of the mantle. When the mantle edge reaches the
muscle, the latter is almost completely covered by a horn-like ridge of
brownish deposited shell material and atrophies. Such destruction
naturally leads to gaping.
6. Odostomia tri$da Totten, 1834. (Figs. 186 and 187)
Fretter and Graham (1949) have listed Odostomia trijda as a
parasite of M y a arenaria.
Description. About 3-5 mm long ; shell pale greenish-white, conical,
with five or six whorls, each separated by a well-defined suture ; two
or three impressed lines below suture giving shell the appearance of
having multiple sutures; aperture oval; outer lip simple; inner lip
with a single oblique fold.
Ecology. This species is often found off of its host(s) under stones and
driftwood at low tide.
7. Other Pyramidellids
In addition to the six species given above, two others have been
reported associated with commercially important pelecypods. Cole
and Hancock (1955) have reported Chrysallida obtusa attached to
oysters, most probably Ostrea edulis, from Salcombe harbour, England,
and Verrill (1873) found a species referred to by him as Turbonilla
interrupta associated with ‘‘ Pecten and other shells ” in Vineyard
Sound, Massachusetts. Since the shells on which Verrill found T .
interrupta were empty, it cannot be definitely stated at this time whether
this gastropod was a parasite of the living animals.