312
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
medial distal angle of terminal segment ; lobes of genital segment with
a small seta on posterior margin ; denticles in posterior margin of anal
segment longer than those on female.
14. Other Pseudomyicoliids
I n addition to the pseudomyicolids given above, Humes (1958b)
described Pseudomyicola mirabilis from the mantle cavity of Arca
decussata collected a t Nossi-Bk, Madagascar. Later, Humes and
Cressey (1958) reported finding the same copepod in A . senilis collected
at Somone, Senegal, in Ostrea tulipa from the same locality, and in
Pitar tumens a t Haan, Senegal. Since these pelecypod hosts are of
limited commercial importance, P. mirabilis is being briefly recorded
herein.
15. Tisbe celata Humes, 1954. (Figs. 210 and 211)
(Order Harpacticoida; family Tisbidae)
The genus Tisbe includes twenty-seven recognized species and several
doubtful ones. Among these, only two, T . wilsoni and T . celata, have
been found as symbionts, possibly parasites, while two others, T .
elongata and T . furcata, which are usually free-living, have been found
in association with other invertebrates. Specifically, T . wilsoni was
described by Seiwell (1928) as a " commensal " from Amaroucium a t
Woods Hole, Massachusetts, and T . celata, the species under consideration, was described by Humes (1954a) from the mantle cavity of Mytilus
edulis collected a t St. Andrews, New Brunswick, Canada. T . elongata
was recorded by Gurney (1933) and Leigh-Sharpe (1935) on the gills of
Homarus vulgaris, and T . furcata was found by Aurivillius (1885, 1887)
in the tunicate Molgula ampulloides.
Relative to T . celata, Humes (1954a) is of the opinion that it is a
parasite of Mytilus edulis.
Description. Adult female (Fig. 210) colorless except for bright
red eye and pale orange egg sac ; total length (from tip of rostrum to
tip of caudal rami) 0.929-0.979 mm (average 0.961 mm); greatest
width, a t level of first thoracic segment, 0.415 mm ; genital segment,
0.641 mm long, distinctly divided dorsally and laterally by transverse
furrow; first four thoracic segments and genital segment each with
minute slender seta, 0.010 mm long, located near posterolateral margin
in addition to a pair of similar setae in front of transverse furrow;
abdomen of three segments ; anal operculum as a smooth flap ; rostrum,
0.028 mm long, broadly rounded, with two minute setae; second
thoracic segment 0.115 mm long; third thoracic segment 0-103 mm
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
medial distal angle of terminal segment ; lobes of genital segment with
a small seta on posterior margin ; denticles in posterior margin of anal
segment longer than those on female.
14. Other Pseudomyicoliids
I n addition to the pseudomyicolids given above, Humes (1958b)
described Pseudomyicola mirabilis from the mantle cavity of Arca
decussata collected a t Nossi-Bk, Madagascar. Later, Humes and
Cressey (1958) reported finding the same copepod in A . senilis collected
at Somone, Senegal, in Ostrea tulipa from the same locality, and in
Pitar tumens a t Haan, Senegal. Since these pelecypod hosts are of
limited commercial importance, P. mirabilis is being briefly recorded
herein.
15. Tisbe celata Humes, 1954. (Figs. 210 and 211)
(Order Harpacticoida; family Tisbidae)
The genus Tisbe includes twenty-seven recognized species and several
doubtful ones. Among these, only two, T . wilsoni and T . celata, have
been found as symbionts, possibly parasites, while two others, T .
elongata and T . furcata, which are usually free-living, have been found
in association with other invertebrates. Specifically, T . wilsoni was
described by Seiwell (1928) as a " commensal " from Amaroucium a t
Woods Hole, Massachusetts, and T . celata, the species under consideration, was described by Humes (1954a) from the mantle cavity of Mytilus
edulis collected a t St. Andrews, New Brunswick, Canada. T . elongata
was recorded by Gurney (1933) and Leigh-Sharpe (1935) on the gills of
Homarus vulgaris, and T . furcata was found by Aurivillius (1885, 1887)
in the tunicate Molgula ampulloides.
Relative to T . celata, Humes (1954a) is of the opinion that it is a
parasite of Mytilus edulis.
Description. Adult female (Fig. 210) colorless except for bright
red eye and pale orange egg sac ; total length (from tip of rostrum to
tip of caudal rami) 0.929-0.979 mm (average 0.961 mm); greatest
width, a t level of first thoracic segment, 0.415 mm ; genital segment,
0.641 mm long, distinctly divided dorsally and laterally by transverse
furrow; first four thoracic segments and genital segment each with
minute slender seta, 0.010 mm long, located near posterolateral margin
in addition to a pair of similar setae in front of transverse furrow;
abdomen of three segments ; anal operculum as a smooth flap ; rostrum,
0.028 mm long, broadly rounded, with two minute setae; second
thoracic segment 0.115 mm long; third thoracic segment 0-103 mm