8. THE PHYLUM MOLLUSCA
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have recorded it in association with Mytilus edulis. While feeding on
Chlarnp opercularis, it does not orient itself on the “ ears ” of the scallop
as does 0. eulirnoides, but sits near the ventral edge of the shell as it
does on Mytilus edulis. The specimens of Chlamys opercularis used
during this study were small and, according to Ankel’s (1959) earlier
report, it is perhaps doubtful if feeding could take place from its position
on the shell on larger scallops.
0. rissoides, a species reported by Pelseneer (1914) as a parasite on
Mytilus, is considered a synonym of 0. scdaris by Jeffreys (1867) and
several subsequent authors.
Description. About 4-5 mm long; shell white and polished, subconical, with five to six whorls ; each whorl slightly ballooned and with
summit with strongly tabulated shoulder ; post-nuclear whorls similarly
sculptured throughout ; spiral sculpture absent or as extremely fine
microscopic lines of growth or striae ; varices absent ; with outer lip at
edge of aperture ; with fold at base of columella.
Other information. Ankel and Christensen (1963) have noted that
0. scalaris will feed on hosts which are smaller than itself; for example,
Hydrobia ulvae and Rissoa membranacea.
5. Odostomia eulimoides Hanley, 1844 (=O. pallida Montagu)*
This species was the first pyramidellid to be reported as a parasite.
Jeffreys (1867) has stated that it occurs “ chiefly (if not only) on the
ears of Pecten (=Chlamys) opercularis and P. (= Aequipecten) maxirnus,
in the coralline zone ; it is widely distributed and rather common. The
trawl-refuse a t Plymouth and Brixham is especially productive of this
shell.” It has also been reported as a parasite of Pecten islandicus by
Sars (1878), of P. jacobaeus by Kobelt (1886)) of Mytilus edulis by
Marshall (1899), of Turritella comrnunis by Smart (1887), and of Xaxicava
rugosa by Ankel(l959). Fretter and Graham (1949) and Graham (1955)
have restated Jeffreys’ observations while Cole (1951b) has reported it
as a parasite of oysters (most probably Ostrea edulis) in British waters.
Cole and Hancock (1955) have reported it on Mytilus edulis in addition
to Ostrea edulis.
On both mussels and oysters this snail is found lodged in small
pockets inside the ventral margin of the shell. The pockets had resulted
from the withdrawal of the mantle in response to the irritation caused
(Class Gastropoda; subclass Opisthobranchia; family Pyramidellidae)
* According to Jeffreys (1867), 0. eulimoides is a synonym of 0. pall& and the letter
name has priority. For some reason undetermined by me, the more recent authors have
all designated this snail as 0. eulirnoidea.
283
have recorded it in association with Mytilus edulis. While feeding on
Chlarnp opercularis, it does not orient itself on the “ ears ” of the scallop
as does 0. eulirnoides, but sits near the ventral edge of the shell as it
does on Mytilus edulis. The specimens of Chlamys opercularis used
during this study were small and, according to Ankel’s (1959) earlier
report, it is perhaps doubtful if feeding could take place from its position
on the shell on larger scallops.
0. rissoides, a species reported by Pelseneer (1914) as a parasite on
Mytilus, is considered a synonym of 0. scdaris by Jeffreys (1867) and
several subsequent authors.
Description. About 4-5 mm long; shell white and polished, subconical, with five to six whorls ; each whorl slightly ballooned and with
summit with strongly tabulated shoulder ; post-nuclear whorls similarly
sculptured throughout ; spiral sculpture absent or as extremely fine
microscopic lines of growth or striae ; varices absent ; with outer lip at
edge of aperture ; with fold at base of columella.
Other information. Ankel and Christensen (1963) have noted that
0. scalaris will feed on hosts which are smaller than itself; for example,
Hydrobia ulvae and Rissoa membranacea.
5. Odostomia eulimoides Hanley, 1844 (=O. pallida Montagu)*
This species was the first pyramidellid to be reported as a parasite.
Jeffreys (1867) has stated that it occurs “ chiefly (if not only) on the
ears of Pecten (=Chlamys) opercularis and P. (= Aequipecten) maxirnus,
in the coralline zone ; it is widely distributed and rather common. The
trawl-refuse a t Plymouth and Brixham is especially productive of this
shell.” It has also been reported as a parasite of Pecten islandicus by
Sars (1878), of P. jacobaeus by Kobelt (1886)) of Mytilus edulis by
Marshall (1899), of Turritella comrnunis by Smart (1887), and of Xaxicava
rugosa by Ankel(l959). Fretter and Graham (1949) and Graham (1955)
have restated Jeffreys’ observations while Cole (1951b) has reported it
as a parasite of oysters (most probably Ostrea edulis) in British waters.
Cole and Hancock (1955) have reported it on Mytilus edulis in addition
to Ostrea edulis.
On both mussels and oysters this snail is found lodged in small
pockets inside the ventral margin of the shell. The pockets had resulted
from the withdrawal of the mantle in response to the irritation caused
(Class Gastropoda; subclass Opisthobranchia; family Pyramidellidae)
* According to Jeffreys (1867), 0. eulimoides is a synonym of 0. pall& and the letter
name has priority. For some reason undetermined by me, the more recent authors have
all designated this snail as 0. eulirnoidea.