6. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTHES
215
nucleus of the pearl. But if it is ingested by the avian host before the
pearly wall is formed, it will attain maturity.
Nothing is known about the ecology of G.
margaritarum except that it is apparently widely distributed throughout Europe. Nothing is known about its physiology. Histopathological
changes in Cardium or Tapes resulting from the presence of sporocysts
have not been studied. Similarly, other than Jameson’s (1902) account
of pearl formation around the metacercaria, other changes, if any, in
M . edulis are not known.
Other information.
7. Metacercaria (Gymnophallus) strigata Lebour, 1908. (Fig. 122)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Azygiata;
This gymnophallid parasite was originally described as Cercaria
strigata by Lebour (1908, 1911) but there is no doubt that the form
described by her is a metacercaria. It is found between the mantle and
shell of Tellina tenuis and Donax vittatus a t Alnmouth, Northumberland,
England, and in Tellina tenuis a t Millport, Scotland. The sporocyst has
since been found by Rees (1939a) in Cardium edule collected a t the
Dovey estuary, Wales. Giard (1907) is of the opinion that Metacercaria
strigata is the larva of Gymnophallus somateriae but this has not been
proven.
Sporocyst (in digestive gland of
Cardium edule) thin-walled, colorless, ovoid, contains cercariae at
various stages of development. Cercariae removed from sporocysts
“ show the same structure as the metacercaria ” (Rees, 1939a).
Metacercaria (Fig. 122) (on mantle of Tellinn tenuis and Donas vittatus)
broadly ovate, tapers slightly to posterior extremity, 0.17-0.40 mm long,
0.30-0.396 mm? wide (Rees reported the maximum width to be 0-095
mni which is obviously a misprint), armed with cuticular spines;
anterior sucker 0.09 x 0.075 mm, ventral sucker, 0.05 x 0.048 mm,
situated slightly posterior to midlength of body ; prepharynx absent ;
pharynx 0.025 x 0.021 mm ; esophagus short ; intestinal caeca bulbous,
capable of expanding and contracting, extending to anterior border of
ventral sucker ; large number of glands a t anterior extremity around
anterior sucker with ducts opening by a series of pores along dorsal
border of mouth ; excretory vesicle, lyre-shaped (Y-shaped with lateral
projection off of arms), with arms reaching level of anterior sucker;
flame-cell pattern 2 [ ( 2 + 2) + (2 + a ) ] ; two oval testes, each measuring 0-05 x 0-024 mm, one on each side midway between ventral sucker
and posterior body terminal ; single ovoid ovary, 0-03 x 0.02 mm, in
front of right testis.
superfamily Fellodistomatoidea; family Fellodistomatidae)
Description of stages in mollusc.
215
nucleus of the pearl. But if it is ingested by the avian host before the
pearly wall is formed, it will attain maturity.
Nothing is known about the ecology of G.
margaritarum except that it is apparently widely distributed throughout Europe. Nothing is known about its physiology. Histopathological
changes in Cardium or Tapes resulting from the presence of sporocysts
have not been studied. Similarly, other than Jameson’s (1902) account
of pearl formation around the metacercaria, other changes, if any, in
M . edulis are not known.
Other information.
7. Metacercaria (Gymnophallus) strigata Lebour, 1908. (Fig. 122)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Azygiata;
This gymnophallid parasite was originally described as Cercaria
strigata by Lebour (1908, 1911) but there is no doubt that the form
described by her is a metacercaria. It is found between the mantle and
shell of Tellina tenuis and Donax vittatus a t Alnmouth, Northumberland,
England, and in Tellina tenuis a t Millport, Scotland. The sporocyst has
since been found by Rees (1939a) in Cardium edule collected a t the
Dovey estuary, Wales. Giard (1907) is of the opinion that Metacercaria
strigata is the larva of Gymnophallus somateriae but this has not been
proven.
Sporocyst (in digestive gland of
Cardium edule) thin-walled, colorless, ovoid, contains cercariae at
various stages of development. Cercariae removed from sporocysts
“ show the same structure as the metacercaria ” (Rees, 1939a).
Metacercaria (Fig. 122) (on mantle of Tellinn tenuis and Donas vittatus)
broadly ovate, tapers slightly to posterior extremity, 0.17-0.40 mm long,
0.30-0.396 mm? wide (Rees reported the maximum width to be 0-095
mni which is obviously a misprint), armed with cuticular spines;
anterior sucker 0.09 x 0.075 mm, ventral sucker, 0.05 x 0.048 mm,
situated slightly posterior to midlength of body ; prepharynx absent ;
pharynx 0.025 x 0.021 mm ; esophagus short ; intestinal caeca bulbous,
capable of expanding and contracting, extending to anterior border of
ventral sucker ; large number of glands a t anterior extremity around
anterior sucker with ducts opening by a series of pores along dorsal
border of mouth ; excretory vesicle, lyre-shaped (Y-shaped with lateral
projection off of arms), with arms reaching level of anterior sucker;
flame-cell pattern 2 [ ( 2 + 2) + (2 + a ) ] ; two oval testes, each measuring 0-05 x 0-024 mm, one on each side midway between ventral sucker
and posterior body terminal ; single ovoid ovary, 0-03 x 0.02 mm, in
front of right testis.
superfamily Fellodistomatoidea; family Fellodistomatidae)
Description of stages in mollusc.