6. THE PHYLA PORIFERA, CNIDARIA AND PLATYHELMINTHES
243
30. Unidentified Echinostome of Nicoll, 1906. Himasthla sp.? (Fig. 148)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
During a survey of the parasites of Cardiurn edule collected a t the
mouth of the Eden, northern England, Nicoll (1906a) found an echinostome metacercaria encysted along the inner mantle fold and in the
foot musculature. He did not name this larva but did give a brief
description. According to him, the adult is an intestinal parasite of
the oyster-catcher, Haernatopus ostralegus, although experimental
proof was not provided. Neither his description of the adult nor his
illustration of what is assumed to be a very young adult are sufficient
to attempt a definite identification although the occurrence of a conspicuous spinous collar and the positions of its suckers definitely establish it as an echinostome, probably a member of the genus Himasthla.
Moreover, the morphology of the metacercaria and the fact that it
encysts in a pelecypod suggest that it is a species of Himasthla or some
closely allied genus.
Cyst transparent, slightly brownish,
0.21-0.25 mm in diameter ; cyst wall comprised of three layers which
collectively measure around 0.13 mm in width. Metacercaria (Fig.
148) 0.6-0.8 mm long x 0.19 mm a t its greatest width; cuticle
armed with thirty to forty alternate rows of conspicuous spines in
anterior half of body ; anterior sucker, 0.095 mm in diameter, smaller
than ventral sucker ; slender prepharynx, pharynx (0.05 mm x 0.03 mm),
and long slender esophagus present ; termination of intestinal caeca
undetermined ; ventral sucker immediately posterior to midlength
of body ; reniform collar armed with twenty-nine spines each measuring
0.025 mm long except for last three on each end which are smaller;
excretory vesicle with long lateral collecting tubules, with side
branches, reaching to posterior margin of collar.
Description of metacercaria.
31. Parorchis acanthus Nicoll, 1906. (Figs. 149 and 150)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Philophthalmidae)
The adult of Parorchis acanthus was originally described by Nicoll
(1906b) from the bursa Pabricii and cloaca of the herring gull, Larus
argentatus, under the name Zeugorchis acanthus. Later (Nicoll, 1907a),
he erected tho genus Parorchis and placed P. acanthus therein. Linton
(1914) described P. avitus also from Larus argentatus, but since then
Cable and Martin (1936) have demonstrated that it is a synonym of
P . acanthus although earlier Stunkard and Cable (1932), who carried
243
30. Unidentified Echinostome of Nicoll, 1906. Himasthla sp.? (Fig. 148)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
During a survey of the parasites of Cardiurn edule collected a t the
mouth of the Eden, northern England, Nicoll (1906a) found an echinostome metacercaria encysted along the inner mantle fold and in the
foot musculature. He did not name this larva but did give a brief
description. According to him, the adult is an intestinal parasite of
the oyster-catcher, Haernatopus ostralegus, although experimental
proof was not provided. Neither his description of the adult nor his
illustration of what is assumed to be a very young adult are sufficient
to attempt a definite identification although the occurrence of a conspicuous spinous collar and the positions of its suckers definitely establish it as an echinostome, probably a member of the genus Himasthla.
Moreover, the morphology of the metacercaria and the fact that it
encysts in a pelecypod suggest that it is a species of Himasthla or some
closely allied genus.
Cyst transparent, slightly brownish,
0.21-0.25 mm in diameter ; cyst wall comprised of three layers which
collectively measure around 0.13 mm in width. Metacercaria (Fig.
148) 0.6-0.8 mm long x 0.19 mm a t its greatest width; cuticle
armed with thirty to forty alternate rows of conspicuous spines in
anterior half of body ; anterior sucker, 0.095 mm in diameter, smaller
than ventral sucker ; slender prepharynx, pharynx (0.05 mm x 0.03 mm),
and long slender esophagus present ; termination of intestinal caeca
undetermined ; ventral sucker immediately posterior to midlength
of body ; reniform collar armed with twenty-nine spines each measuring
0.025 mm long except for last three on each end which are smaller;
excretory vesicle with long lateral collecting tubules, with side
branches, reaching to posterior margin of collar.
Description of metacercaria.
31. Parorchis acanthus Nicoll, 1906. (Figs. 149 and 150)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Philophthalmidae)
The adult of Parorchis acanthus was originally described by Nicoll
(1906b) from the bursa Pabricii and cloaca of the herring gull, Larus
argentatus, under the name Zeugorchis acanthus. Later (Nicoll, 1907a),
he erected tho genus Parorchis and placed P. acanthus therein. Linton
(1914) described P. avitus also from Larus argentatus, but since then
Cable and Martin (1936) have demonstrated that it is a synonym of
P . acanthus although earlier Stunkard and Cable (1932), who carried