278
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
For example, the characteristics recognized by Dall and Bartsch (1909)
in their monograph on the western American pyramidellids are considerably more conservative than those employed by Laseron (1951,
1959) in his papers on the species of Australia. No attempt is being
made in this paper to resolve the taxonomic problems involved. For
a good account of the morphology and development of pyramidellids,
the reader is referred to Fretter and Graham (1949).
As the pyramidellids are now recognized not to be as host-specific
as originally thought, the species included in this review cannot
definitely be said to be the only parasites associated with the hosts
under consideration. Other yet unknown species will undoubtedly be
found associated with commercially important molluscs. The following
are those species which have been reported from such molluscs. In
addition to the specific characteristics given for each species under
consideration, it is noted that the species of Odostomia all possess a
tooth on the columella, i.e. a tooth-shaped projection on its lower end.
According to Fretter and Graham (1962)) this " tooth " is " probably
due to secretion of material over the surface of the columella by a
mantle which has outgrown the space available for it and which has
therefore become folded." Also, the shell includes a heterostrophic
apex.
1. Odostomia impressa Say, 1822. (Figs. 180 and 181)
(Class Gastropoda; subclass Opisthobranchia; order Tectibranchia; family
Pyramidellidae )
Odostomia impressa has been reported by Hopkins (19564, Allen
(1958) and Wells (1959) t o feed on Crassostrea virginica. It is not
specific for this oyster since Allen has demonstrated that it will also
feed on the prosobranchs Bittiurn varium, Crepidula convexa, Triphora
nigrocincta and Urosalpinx cinerea, as well as a polychaete and the
tunicate Molgula.
Description. About 7 mm long, although younger specimens attached
to oysters may be as small as 0.7 m m ; shell milky white, elongate,
consisting of six or seven rather flattened whorls ; with channeled
sutures ; surface with three equally spaced spiral grooves ; aperture
oval, with outer lip thin and sharp, occasionally slightly flared in
older shells.
Ecology. According to Morris (1947), this species ranges from
southern New England to the Gulf of Mexico and is commonly found
on oyster beds. Hopkins ( 1 9 5 6 ~ )
has shown that, unlike 0. bisuturalis,
0. impressa prefers large oysters. Furthermore : " Rough surfaces, such
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
For example, the characteristics recognized by Dall and Bartsch (1909)
in their monograph on the western American pyramidellids are considerably more conservative than those employed by Laseron (1951,
1959) in his papers on the species of Australia. No attempt is being
made in this paper to resolve the taxonomic problems involved. For
a good account of the morphology and development of pyramidellids,
the reader is referred to Fretter and Graham (1949).
As the pyramidellids are now recognized not to be as host-specific
as originally thought, the species included in this review cannot
definitely be said to be the only parasites associated with the hosts
under consideration. Other yet unknown species will undoubtedly be
found associated with commercially important molluscs. The following
are those species which have been reported from such molluscs. In
addition to the specific characteristics given for each species under
consideration, it is noted that the species of Odostomia all possess a
tooth on the columella, i.e. a tooth-shaped projection on its lower end.
According to Fretter and Graham (1962)) this " tooth " is " probably
due to secretion of material over the surface of the columella by a
mantle which has outgrown the space available for it and which has
therefore become folded." Also, the shell includes a heterostrophic
apex.
1. Odostomia impressa Say, 1822. (Figs. 180 and 181)
(Class Gastropoda; subclass Opisthobranchia; order Tectibranchia; family
Pyramidellidae )
Odostomia impressa has been reported by Hopkins (19564, Allen
(1958) and Wells (1959) t o feed on Crassostrea virginica. It is not
specific for this oyster since Allen has demonstrated that it will also
feed on the prosobranchs Bittiurn varium, Crepidula convexa, Triphora
nigrocincta and Urosalpinx cinerea, as well as a polychaete and the
tunicate Molgula.
Description. About 7 mm long, although younger specimens attached
to oysters may be as small as 0.7 m m ; shell milky white, elongate,
consisting of six or seven rather flattened whorls ; with channeled
sutures ; surface with three equally spaced spiral grooves ; aperture
oval, with outer lip thin and sharp, occasionally slightly flared in
older shells.
Ecology. According to Morris (1947), this species ranges from
southern New England to the Gulf of Mexico and is commonly found
on oyster beds. Hopkins ( 1 9 5 6 ~ )
has shown that, unlike 0. bisuturalis,
0. impressa prefers large oysters. Furthermore : " Rough surfaces, such