6. THE PHYLA PORIBERA, CNIDARIA AND PLATYHELMINTHES
217
this unlikely. Rees has suggested that it may be the larva of either G.
macroporus, an intestinal parasite of Melanitta (=Oidemia) nigra, or
G. deliciosus, a parasite of Larus argentatus, L. fuscus and L. canus, but
experimental data are wanting.
Relative to the infection of the second intermediate host, either
Tellina tenuis or Donax vittatus, Rees (1939a) has suggested that the
cephalic glands found in cercariae (and metacercariae) " are probably
histolytic in function, and enable the cercaria to bore its way out of the
digestive gland of its first intermediate host, and also to bore through
to the outside of the mantle of its second intermediate host ". This,
although possible, remains to be demonstrated.
8. Metacercaria (Gymnophallus) megalocoela Palombi, 1934. (Figs. 123
and 124)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Azygiata;
superfamily Fellodistomatoidea; family Fellodistomatidae)
Only the metacercarial stage of Gymnophallus megalocoela is known.
It was described by Palombi (1934a) from between the shell and mantle
of Tapes decussatus (=Amygdala decussata) collected in the Gulf of
Naples. The metacercaria is said to be covered by a thick ellipsoid
gelatinous coat of host origin impregnated with calcium particles
(Fig. 123). This coat appears to be comparable to the " jelly-like
mass " described by Lebour (1911) in which G. margaritarum metacercariae are found.
Description. Gelatinous cyst (Fig. 123) fairly transparent, 0.36 mm
in diameter. Metacercaria (Fig. 124) ovoid, 0.21-0.29 mm long, 0.220.23 mm wide ; body covered with minute cuticular spines ; anterior
sucker 0.07-0-08 mm in diameter ; ventral sucker, 0.03 mm in diameter,
in posterior half of body ; prepharynx absent ; pharynx and extremely
short esophagus present ; pharynx averages 0.02 mm in diameter ;
intestinal caeca large and globose, 0-11-0-13 mm long x 0.08-0.09
mm wide, reaching slightly past level of ventJral sucker; two testes
present, one on each side of stem of excretory vesicle ; ovary anterolateral to right testis ; excretory vesicle Y-shaped, large, with arms
reaching level of anterior sucker.
Other information. Nothing else is known about 0. megalocoela.
From what is known about the life cycle pattern among gymnophallids,
Tapes decussatus is undoubtedly the second intermediate host while
some other pelecypod is the first. The definitive host is most probably
one or more species of shore birds.
217
this unlikely. Rees has suggested that it may be the larva of either G.
macroporus, an intestinal parasite of Melanitta (=Oidemia) nigra, or
G. deliciosus, a parasite of Larus argentatus, L. fuscus and L. canus, but
experimental data are wanting.
Relative to the infection of the second intermediate host, either
Tellina tenuis or Donax vittatus, Rees (1939a) has suggested that the
cephalic glands found in cercariae (and metacercariae) " are probably
histolytic in function, and enable the cercaria to bore its way out of the
digestive gland of its first intermediate host, and also to bore through
to the outside of the mantle of its second intermediate host ". This,
although possible, remains to be demonstrated.
8. Metacercaria (Gymnophallus) megalocoela Palombi, 1934. (Figs. 123
and 124)
(Superorder Anepitheliocystidia; order Strigeatoidea; suborder Azygiata;
superfamily Fellodistomatoidea; family Fellodistomatidae)
Only the metacercarial stage of Gymnophallus megalocoela is known.
It was described by Palombi (1934a) from between the shell and mantle
of Tapes decussatus (=Amygdala decussata) collected in the Gulf of
Naples. The metacercaria is said to be covered by a thick ellipsoid
gelatinous coat of host origin impregnated with calcium particles
(Fig. 123). This coat appears to be comparable to the " jelly-like
mass " described by Lebour (1911) in which G. margaritarum metacercariae are found.
Description. Gelatinous cyst (Fig. 123) fairly transparent, 0.36 mm
in diameter. Metacercaria (Fig. 124) ovoid, 0.21-0.29 mm long, 0.220.23 mm wide ; body covered with minute cuticular spines ; anterior
sucker 0.07-0-08 mm in diameter ; ventral sucker, 0.03 mm in diameter,
in posterior half of body ; prepharynx absent ; pharynx and extremely
short esophagus present ; pharynx averages 0.02 mm in diameter ;
intestinal caeca large and globose, 0-11-0-13 mm long x 0.08-0.09
mm wide, reaching slightly past level of ventJral sucker; two testes
present, one on each side of stem of excretory vesicle ; ovary anterolateral to right testis ; excretory vesicle Y-shaped, large, with arms
reaching level of anterior sucker.
Other information. Nothing else is known about 0. megalocoela.
From what is known about the life cycle pattern among gymnophallids,
Tapes decussatus is undoubtedly the second intermediate host while
some other pelecypod is the first. The definitive host is most probably
one or more species of shore birds.