R. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTHES
235
posterior to midlength of body ; body covered with fine cuticular spines ;
no tail in fully developed form ; immature cercaria with small knob-like
tail ; no stylet or other structures specialized for penetration at anterior
end ; prepharynx not usually visible in frontal view ; pharynx muscular,
averaging 0.045 mm long x 0.035-0.040 mm wide ; esophagus approximately of same length as pharynx ; intestinal caeca reaching to near
posterior body terminal; six small cephalic glands on each side of
pharynx, with ducts running dorsally over anterior sucker to anterior
end ; anlage of cirrus pouch immediately anterior to ventral sucker ;
anlager of testes and ovary immediately posterior to ventral sucker ;
excretory vesicle Y-shaped, with sac-like stem terminating anteriorIy
behind gonadal anlagen ; club-shaped arms extend anteriorly to level of
caecal bifurcation; flame-cell pattern 2[(2 + 2) + (2 + 2)]
Nothing else is known about C. brachidontis
except that Hopkins (1954b), as the result of not finding metacercariae
in forty Brachidontes recurvus and ( ( hundreds ” of oysters from the
area where the infected mussels were found, concluded : “ Therefore
it seems improbable that Cercaria brachidontis uses bivalve molluscs as
second intermediate hosts.’’
Other information.
24. Himasthla leptosoma Creplin, 1829. (Fig. 144)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
Nicoll (1906a,b) reported the occurrence of an echinostome metacercaria encysted in Cardium edule, Mytilus edulis and Mactra stultorum
which is morphologically sufficiently similar to adults found by him
in the oyster catcher, Haematopus ostmlegus, and herring gull, Larus
argentatus, for him to consider it as the larva of the adult in these birds.
He named this trematode Echinostomum secundum, a designation
adopted by Lebour (1906, 1909, 1911). Although Holliman (1961)
still lists E. secundum as a distinct species, in recent years several
investigators (Sprehn, 1932 ; Palombi, 1934a ; Dawes, 1946 ; Hutton,
1952 ; Yamaguti, 1958) have designated, and probably correctly, E.
secundum as a synonym of Himmthla leptosoma, a species described as
Distoma Zeptosomum by Creplin (1829) and later placed in the genus
Himasthla as H . leptosoma by Dietz (1909).
Not only has Nicoll’s metacercaria been found in the three pelecypods listed above, but Lebour (1911) has also reported it in Mya
arenaria and Tapes pullastra. I n addition, Cubnot (1892, 1917) has
found what he believed to be H . leptosoma metacercariae encysted in the
circumoral tentacles of the holothurian Leptosynapta inhoerens in
235
posterior to midlength of body ; body covered with fine cuticular spines ;
no tail in fully developed form ; immature cercaria with small knob-like
tail ; no stylet or other structures specialized for penetration at anterior
end ; prepharynx not usually visible in frontal view ; pharynx muscular,
averaging 0.045 mm long x 0.035-0.040 mm wide ; esophagus approximately of same length as pharynx ; intestinal caeca reaching to near
posterior body terminal; six small cephalic glands on each side of
pharynx, with ducts running dorsally over anterior sucker to anterior
end ; anlage of cirrus pouch immediately anterior to ventral sucker ;
anlager of testes and ovary immediately posterior to ventral sucker ;
excretory vesicle Y-shaped, with sac-like stem terminating anteriorIy
behind gonadal anlagen ; club-shaped arms extend anteriorly to level of
caecal bifurcation; flame-cell pattern 2[(2 + 2) + (2 + 2)]
Nothing else is known about C. brachidontis
except that Hopkins (1954b), as the result of not finding metacercariae
in forty Brachidontes recurvus and ( ( hundreds ” of oysters from the
area where the infected mussels were found, concluded : “ Therefore
it seems improbable that Cercaria brachidontis uses bivalve molluscs as
second intermediate hosts.’’
Other information.
24. Himasthla leptosoma Creplin, 1829. (Fig. 144)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
Nicoll (1906a,b) reported the occurrence of an echinostome metacercaria encysted in Cardium edule, Mytilus edulis and Mactra stultorum
which is morphologically sufficiently similar to adults found by him
in the oyster catcher, Haematopus ostmlegus, and herring gull, Larus
argentatus, for him to consider it as the larva of the adult in these birds.
He named this trematode Echinostomum secundum, a designation
adopted by Lebour (1906, 1909, 1911). Although Holliman (1961)
still lists E. secundum as a distinct species, in recent years several
investigators (Sprehn, 1932 ; Palombi, 1934a ; Dawes, 1946 ; Hutton,
1952 ; Yamaguti, 1958) have designated, and probably correctly, E.
secundum as a synonym of Himmthla leptosoma, a species described as
Distoma Zeptosomum by Creplin (1829) and later placed in the genus
Himasthla as H . leptosoma by Dietz (1909).
Not only has Nicoll’s metacercaria been found in the three pelecypods listed above, but Lebour (1911) has also reported it in Mya
arenaria and Tapes pullastra. I n addition, Cubnot (1892, 1917) has
found what he believed to be H . leptosoma metacercariae encysted in the
circumoral tentacles of the holothurian Leptosynapta inhoerens in