232
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
of body ; tail may or may not be lost prior to emergence ; excretory
vesicle Y-shaped, arms longer than stem, extending anteriorly to level
of caecal bifurcation ; unicellular cystogenous glands present throughout body; three pairs of cephalic gland ducts emanate from postpharyngeal region and terminate in six distinct pores on dorsal lip of
anterior sucker (actual glands not seen by Uzmann (1953) but Stunkard
and Uzmann (1959) have depicted glands located on each side of
esophagus immediately anterior to caecal bifurcation. I n addition,
they reported two additional pairs of ducts arising from cell bodies
located lateral to the preacetabular area) ; flame-cell pattern 2[(2 + 2) +
Metacercaria progenetic, elongate, 2.0 mm long, 0.8 mm wide;
anterior sucker 0.18 mm x 0.22 mm; ventral sucker 0.34 mm x
0.37 mm; pharynx 0.125 mm x 0.150 mm; esophagus short; intestinal
caeca reaching beyond level of testes to near posterior end of body;
testes obliquely arranged in posterior one-third of body, each testis
measures 0.17 mm x 0-15 mm; ovary between anterior testis and
ventral sucker, 0.15 mm x 0.14 mm; cirrus pouch enclosing cirrus
anterior to ventral sucker.
Adult (from Mytilus edulis) 2.4 mm-3.2 mm (average 2.74 mm)
long, 0.6 mm-0.92 mm (average 0.81 mm) wide; aspinous; anterior
sucker 0.24 mm x 0.21-0.32 mm (average 0.30 mm) ; pharynx 0.160.20 mm (average 0.18 mm) in diameter; extremely short or no esophagus ; intestinal caeca reaching posterior one-fifth of body ; testes in
posterior half of middle one-third of body, anterior testis 0.15-0.20 mm
(average 0.18 mm), posterior testis 0.16-0.23 mm (average 0.19 mm);
sterile and abnormal, 0.055 mm x 0.026 mm.
Normally the metacercaria of P. maculatus found in
Mytilus edulis is ingested by the definitive fish host within which it
develops to maturity. But, as has been demonstrated by Stunkard
and Uzmann (1959) for P. maculatus and Freeman and Llewellyn (1958)
for P. subtenuis, the progenetic metacercariae of Proctoeces are capable
of developing to sexually mature adults in the molluscan intermediate
host although these produce small and abnormal sterile eggs.
Ecology. The production of cercariae in P. maculatus sporocysts
appears to be temperature influenced. Uzmann (1953) has shown that
the smaller germ-ball-bearing sporocysts (most probably mother sporocysts) dominate in number during July and August while during the
relatively cooler months of April, May and June, the cercariae-bearing
daughter sporocysts are more plentiful. Moreover, in Mytilus edulis
found in subtidal regions, the numerical dominance of daughter sporo(2 + 211.
Life cycle.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
of body ; tail may or may not be lost prior to emergence ; excretory
vesicle Y-shaped, arms longer than stem, extending anteriorly to level
of caecal bifurcation ; unicellular cystogenous glands present throughout body; three pairs of cephalic gland ducts emanate from postpharyngeal region and terminate in six distinct pores on dorsal lip of
anterior sucker (actual glands not seen by Uzmann (1953) but Stunkard
and Uzmann (1959) have depicted glands located on each side of
esophagus immediately anterior to caecal bifurcation. I n addition,
they reported two additional pairs of ducts arising from cell bodies
located lateral to the preacetabular area) ; flame-cell pattern 2[(2 + 2) +
Metacercaria progenetic, elongate, 2.0 mm long, 0.8 mm wide;
anterior sucker 0.18 mm x 0.22 mm; ventral sucker 0.34 mm x
0.37 mm; pharynx 0.125 mm x 0.150 mm; esophagus short; intestinal
caeca reaching beyond level of testes to near posterior end of body;
testes obliquely arranged in posterior one-third of body, each testis
measures 0.17 mm x 0-15 mm; ovary between anterior testis and
ventral sucker, 0.15 mm x 0.14 mm; cirrus pouch enclosing cirrus
anterior to ventral sucker.
Adult (from Mytilus edulis) 2.4 mm-3.2 mm (average 2.74 mm)
long, 0.6 mm-0.92 mm (average 0.81 mm) wide; aspinous; anterior
sucker 0.24 mm x 0.21-0.32 mm (average 0.30 mm) ; pharynx 0.160.20 mm (average 0.18 mm) in diameter; extremely short or no esophagus ; intestinal caeca reaching posterior one-fifth of body ; testes in
posterior half of middle one-third of body, anterior testis 0.15-0.20 mm
(average 0.18 mm), posterior testis 0.16-0.23 mm (average 0.19 mm);
sterile and abnormal, 0.055 mm x 0.026 mm.
Normally the metacercaria of P. maculatus found in
Mytilus edulis is ingested by the definitive fish host within which it
develops to maturity. But, as has been demonstrated by Stunkard
and Uzmann (1959) for P. maculatus and Freeman and Llewellyn (1958)
for P. subtenuis, the progenetic metacercariae of Proctoeces are capable
of developing to sexually mature adults in the molluscan intermediate
host although these produce small and abnormal sterile eggs.
Ecology. The production of cercariae in P. maculatus sporocysts
appears to be temperature influenced. Uzmann (1953) has shown that
the smaller germ-ball-bearing sporocysts (most probably mother sporocysts) dominate in number during July and August while during the
relatively cooler months of April, May and June, the cercariae-bearing
daughter sporocysts are more plentiful. Moreover, in Mytilus edulis
found in subtidal regions, the numerical dominance of daughter sporo(2 + 211.
Life cycle.