6. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTHES
231
(1959) have since reported its occurrence inMytilus edulis taken in the
Woods Hole, Massachusetts, area. It is of interest to note that Stunkard
and Uzmann have not only found two generations of sporocysts in
addition to cercariae in the molluscan host but also found sexually
mature adults in the mollusc, thus indicating the occurrence of a telescoped life cycle. The adults were identified as Proctoeces maculatus, a
species previously reported in a number of species of bottom-feeding
labroid fishes and porgies (Labrus merula, Crenilabrus pavo, C. griseus
and Blennius ocellaris) from the Mediterranean and Black Sea (Looss,
1901 ; Odhner, 1911), and from Sparus macrocephalus, S. aries, Pagrosomus auratus, Epinephelus akaara and Semicossyphus reticulatus from
the Inland Sea of Japan, and Duymeria JEagellifera from Hamazima,
Japan (Yamaguti, 1938, 1953).
The ability of members of the genus Proctoeces to develop to sexual
maturity in molluscs had been reported earlier by Freeman and
Llewellyn (1958) and Fujita (1925), and more recently by Dollfus (1964).
Freeman and Llewellyn have reported that P. subtenuis, a species
normally parasitic in the hindgut of labrid and sparid marine fishes,
can attain sexual maturity in the renal organ of the pelecypod Scrobicularia plana. Fujita has reported what he considered to be progenetic metacercariae of P. ostreae in the gonads of Crassostrea gigas,
and Dollfus has found progenetic metacercariae of P. progeneticus in
the prosobranch Gibbula. In the case of P. maculatus, sporocysts,
cercariae, metacercariae (juveniles), and adults can all occur in Mytilus
edulis.
Description of stages in mollusc. Mother sporocysts globose and
sacculate, 0.34 mm long (according to Stunkard and Uzmann’s illustration), contains few daughter sporocysts. Daughter sporocyst simple,
sacculate, motile, orange in color, 0.857-1.652 mm (average 1.246 mm)
long, primarily in blood sinuses and lymph spaces in gonad and
digestive gland of host, may contain 100 or more cercariae. Cercaria
(Fig. 141) 0.147-0.525 mm long (living) or 0.221-0.284 mm (average
0.254 mm) long (fixed) x 0-072-0.084 mm (average 0.075 mm) wide ;
anterior sucker, usually longer than wide, 0.040-0.045 mm (average
0.043 mm) long x 0.038-0.041 mm (average 0.038 mm) wide; prepharynx 0.002-0.004 mm long; pharynx subspherical, 0.020 mm x
0.024 mm ; esophagus short ; intestinal caeca extend to level posterior
to bifurcation of excretory vesicle; caecal walls of large polygonal
cells ; ventral sucker 0.045-0-051 mm (average 0-048 mm) in diameter,
slightly larger than anterior sucker ; approximate anterior suckerpharynx-ventral sucker ratio being 2 : 1 : 2 ; small spherical tail, 0.0100.013 mm in diameter, attached to slight invagination at posterior end
231
(1959) have since reported its occurrence inMytilus edulis taken in the
Woods Hole, Massachusetts, area. It is of interest to note that Stunkard
and Uzmann have not only found two generations of sporocysts in
addition to cercariae in the molluscan host but also found sexually
mature adults in the mollusc, thus indicating the occurrence of a telescoped life cycle. The adults were identified as Proctoeces maculatus, a
species previously reported in a number of species of bottom-feeding
labroid fishes and porgies (Labrus merula, Crenilabrus pavo, C. griseus
and Blennius ocellaris) from the Mediterranean and Black Sea (Looss,
1901 ; Odhner, 1911), and from Sparus macrocephalus, S. aries, Pagrosomus auratus, Epinephelus akaara and Semicossyphus reticulatus from
the Inland Sea of Japan, and Duymeria JEagellifera from Hamazima,
Japan (Yamaguti, 1938, 1953).
The ability of members of the genus Proctoeces to develop to sexual
maturity in molluscs had been reported earlier by Freeman and
Llewellyn (1958) and Fujita (1925), and more recently by Dollfus (1964).
Freeman and Llewellyn have reported that P. subtenuis, a species
normally parasitic in the hindgut of labrid and sparid marine fishes,
can attain sexual maturity in the renal organ of the pelecypod Scrobicularia plana. Fujita has reported what he considered to be progenetic metacercariae of P. ostreae in the gonads of Crassostrea gigas,
and Dollfus has found progenetic metacercariae of P. progeneticus in
the prosobranch Gibbula. In the case of P. maculatus, sporocysts,
cercariae, metacercariae (juveniles), and adults can all occur in Mytilus
edulis.
Description of stages in mollusc. Mother sporocysts globose and
sacculate, 0.34 mm long (according to Stunkard and Uzmann’s illustration), contains few daughter sporocysts. Daughter sporocyst simple,
sacculate, motile, orange in color, 0.857-1.652 mm (average 1.246 mm)
long, primarily in blood sinuses and lymph spaces in gonad and
digestive gland of host, may contain 100 or more cercariae. Cercaria
(Fig. 141) 0.147-0.525 mm long (living) or 0.221-0.284 mm (average
0.254 mm) long (fixed) x 0-072-0.084 mm (average 0.075 mm) wide ;
anterior sucker, usually longer than wide, 0.040-0.045 mm (average
0.043 mm) long x 0.038-0.041 mm (average 0.038 mm) wide; prepharynx 0.002-0.004 mm long; pharynx subspherical, 0.020 mm x
0.024 mm ; esophagus short ; intestinal caeca extend to level posterior
to bifurcation of excretory vesicle; caecal walls of large polygonal
cells ; ventral sucker 0.045-0-051 mm (average 0-048 mm) in diameter,
slightly larger than anterior sucker ; approximate anterior suckerpharynx-ventral sucker ratio being 2 : 1 : 2 ; small spherical tail, 0.0100.013 mm in diameter, attached to slight invagination at posterior end