190
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Description. C. carinata resembles C. kozlofi in general size and
shape except that its anterior end is more pointed and there is a pronounced ventral curvature of the entire body. A keel is said to occur
on the convex dorsal body surface along the anterior half. Details of
its thigmotactic ciliature are given by Raabe (1934, 1938) under the
name Hypocomina carinata.
11. Raabella helensis Chatton and Lwoff, 1950. (Figs. 98 and 99)
Other information. Nothing else is known about this species.
(Subclass Holotrichia; order Thigmotrichida; family Ancistrocomidae)
This small and active ciliate was originally described by Raabe
(1938) from the gill surfaces of Mytilus edulis collected at Hel, on the
Gulf of Danzig. Raabe believed it to be Hypocomides mytili (although
it is not the same animal as Chatton and Lwoff’s (1922a) H . mytili
which is now known as Isocomides mytili). In 1950, Chatton and Lwoff
established the genus Raabella with R. helensis, the new designation for
Raabe’s H . mytili, as the genotype. Kozloff (1964b) found R. helensis
on the ctenidia and palps of 80% of the mussels, Mytilus edulis,
collected from San Francisco Bay, California.
Description. According to Raabe (1938), two forms of R. helensis,
major and minor, exist, the latter being consistently smaller. Body of
both forms ovoid, slightly dorsoventrally compressed, narrows to
pointed anterior terminal which bears suctorial tentacle by which the
ciliate is attached to host; major form measures 26-36 p x 19-21 p
(Kozloff’s specimens measured 34-38 p long), minor form measures
17-26 p x 15-17 p ; anteriorly located tentacle hollow and continuous
with canal in endoplasm which leads half way along body length;
tentacle withdrawn while swimming ; anterior portion of central body
surface flattened as thigmotactic area ; body cilia, arranged in longitudinal rows, about 8.5 p long ; macro- and micronuclei spherical ; contractile
vacuole posterior (Kozloff’s specimens possessed an ovoid macronucleus and the contractile vacuole was centrally located).
Ecology. As stated, R. helensis has been found on Mytilus edulis
both in the Gulf of Danzig and in San Francisco Bay. There is some
doubt whether the specimens from these two areas are identical.
MacKinnon and Hawes (1961) have expressed the opinion that
Kozloff’s specimens may represent a new subspecies.
Although the feeding habit of R. helensis has not been studied, the
occurrence of an anterior suctorial tentacle, a feature shared by all the
members of the families Hypocomidae and Ancistrocomidae, suggests
that it may feed on the host’s tissues as in the case of Crebricorna
kozlofi.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Description. C. carinata resembles C. kozlofi in general size and
shape except that its anterior end is more pointed and there is a pronounced ventral curvature of the entire body. A keel is said to occur
on the convex dorsal body surface along the anterior half. Details of
its thigmotactic ciliature are given by Raabe (1934, 1938) under the
name Hypocomina carinata.
11. Raabella helensis Chatton and Lwoff, 1950. (Figs. 98 and 99)
Other information. Nothing else is known about this species.
(Subclass Holotrichia; order Thigmotrichida; family Ancistrocomidae)
This small and active ciliate was originally described by Raabe
(1938) from the gill surfaces of Mytilus edulis collected at Hel, on the
Gulf of Danzig. Raabe believed it to be Hypocomides mytili (although
it is not the same animal as Chatton and Lwoff’s (1922a) H . mytili
which is now known as Isocomides mytili). In 1950, Chatton and Lwoff
established the genus Raabella with R. helensis, the new designation for
Raabe’s H . mytili, as the genotype. Kozloff (1964b) found R. helensis
on the ctenidia and palps of 80% of the mussels, Mytilus edulis,
collected from San Francisco Bay, California.
Description. According to Raabe (1938), two forms of R. helensis,
major and minor, exist, the latter being consistently smaller. Body of
both forms ovoid, slightly dorsoventrally compressed, narrows to
pointed anterior terminal which bears suctorial tentacle by which the
ciliate is attached to host; major form measures 26-36 p x 19-21 p
(Kozloff’s specimens measured 34-38 p long), minor form measures
17-26 p x 15-17 p ; anteriorly located tentacle hollow and continuous
with canal in endoplasm which leads half way along body length;
tentacle withdrawn while swimming ; anterior portion of central body
surface flattened as thigmotactic area ; body cilia, arranged in longitudinal rows, about 8.5 p long ; macro- and micronuclei spherical ; contractile
vacuole posterior (Kozloff’s specimens possessed an ovoid macronucleus and the contractile vacuole was centrally located).
Ecology. As stated, R. helensis has been found on Mytilus edulis
both in the Gulf of Danzig and in San Francisco Bay. There is some
doubt whether the specimens from these two areas are identical.
MacKinnon and Hawes (1961) have expressed the opinion that
Kozloff’s specimens may represent a new subspecies.
Although the feeding habit of R. helensis has not been studied, the
occurrence of an anterior suctorial tentacle, a feature shared by all the
members of the families Hypocomidae and Ancistrocomidae, suggests
that it may feed on the host’s tissues as in the case of Crebricorna
kozlofi.