182
MARINE MOLLUSCS AS HOSTS F O R SYMBIOSES
3. Ancistrum subtruncatum Issel, 1903. (Figs. 83-85)
(Subclass Holotrichia; order Thigmotrichida; family Hemispeiridae)
This species was described by Issel (1903) from the gill surfaces of
Tapes decussatus collected in the Gulf of Naples.
Description. Body ovoid when viewed from lateral aspect, slightly
more blunt a t posterior terminal, laterally flattened ; 37-46 p long x
20-25 p in greatest width ; with nine longitudinal ciliary rows on right
side and twenty-one to twenty-two rows on left side; cytostome as
invagination on left margin for almost one-fourth body length ; rapidly
pulsating contractile vacuole in posterior one-fourth of body ; smaller
food vacuoles in posterior half of body ; elongate ovoid macronucleus
diagonally arranged in anterior half of body ; micronucleus, approximately 4.5 p in diameter, near anterolateral margin of macronucleus.
Other information. According to Issel, A. subtruncatum swims by
gyrating like a pinwheel and changes direction in a bizarre fashion. It
is non-motile when attached to its host.
4. Ancistrum isseli Kahl, 1931. (Figs. 86-88)
(Subclass Holotrichia; order Thigmotrichida; family Hemispeiridae)
I n his paper on thigmotrichous ciliates from the Gulf of Naples,
Issel (1903) described an Ancistrum from the mussel Modiola barbata
and, although he found certain differences between his specimens and
the earlier descriptions of A . mytili, he considered his specimens as
representative of that species. Kahl (1931), however, considered
Issel’s ciliates to represent a new species and named it Ancistruma
isseli (which should be designated as Ancistrum isseli). Kidder (1933c),
who found large numbers of this ciliate in the mussel Modiolus modiolus
at Woods Hole, Massachusetts, and Pelham Bay, New York, is in
agreement with Kahl that A . isseli is distinct from A . mytili. I have
found this ciliate intimately associated with the gill surfaces of Modiolus
modiolus collected in Narragansett Bay, Rhode Island (Fig. 88).
Description. Body oval, 70-88 p (average 77 p) x 31-54 p (average
42 p ) , more pointed at both ends than A. mytili, dorsoventrally
flattened, concave ventrally, convex dorsally, with both surfaces
ciliated ; peristome similar to that of A. mytili but with less prominent
flap under cytostome ; enormous macronucleus occupying center of
body ; micronucleus small and spherical, in> anterior quarter of body ;
numerous food vacuoles in posterior third of body, filled with yellow
pigments; contractile vacuole same as in A . mytili. For a detailed
description of the body ciliature and fibrillar system, see Kidder (1933~).
MARINE MOLLUSCS AS HOSTS F O R SYMBIOSES
3. Ancistrum subtruncatum Issel, 1903. (Figs. 83-85)
(Subclass Holotrichia; order Thigmotrichida; family Hemispeiridae)
This species was described by Issel (1903) from the gill surfaces of
Tapes decussatus collected in the Gulf of Naples.
Description. Body ovoid when viewed from lateral aspect, slightly
more blunt a t posterior terminal, laterally flattened ; 37-46 p long x
20-25 p in greatest width ; with nine longitudinal ciliary rows on right
side and twenty-one to twenty-two rows on left side; cytostome as
invagination on left margin for almost one-fourth body length ; rapidly
pulsating contractile vacuole in posterior one-fourth of body ; smaller
food vacuoles in posterior half of body ; elongate ovoid macronucleus
diagonally arranged in anterior half of body ; micronucleus, approximately 4.5 p in diameter, near anterolateral margin of macronucleus.
Other information. According to Issel, A. subtruncatum swims by
gyrating like a pinwheel and changes direction in a bizarre fashion. It
is non-motile when attached to its host.
4. Ancistrum isseli Kahl, 1931. (Figs. 86-88)
(Subclass Holotrichia; order Thigmotrichida; family Hemispeiridae)
I n his paper on thigmotrichous ciliates from the Gulf of Naples,
Issel (1903) described an Ancistrum from the mussel Modiola barbata
and, although he found certain differences between his specimens and
the earlier descriptions of A . mytili, he considered his specimens as
representative of that species. Kahl (1931), however, considered
Issel’s ciliates to represent a new species and named it Ancistruma
isseli (which should be designated as Ancistrum isseli). Kidder (1933c),
who found large numbers of this ciliate in the mussel Modiolus modiolus
at Woods Hole, Massachusetts, and Pelham Bay, New York, is in
agreement with Kahl that A . isseli is distinct from A . mytili. I have
found this ciliate intimately associated with the gill surfaces of Modiolus
modiolus collected in Narragansett Bay, Rhode Island (Fig. 88).
Description. Body oval, 70-88 p (average 77 p) x 31-54 p (average
42 p ) , more pointed at both ends than A. mytili, dorsoventrally
flattened, concave ventrally, convex dorsally, with both surfaces
ciliated ; peristome similar to that of A. mytili but with less prominent
flap under cytostome ; enormous macronucleus occupying center of
body ; micronucleus small and spherical, in> anterior quarter of body ;
numerous food vacuoles in posterior third of body, filled with yellow
pigments; contractile vacuole same as in A . mytili. For a detailed
description of the body ciliature and fibrillar system, see Kidder (1933~).