23G
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
addition to Arenicola marina and Scrobicularia tenuis plana, and Villot
(1875, 1878) has reported it in 8. tenuis and in isopods.
Description of metacercaria (the stage found in economically
important molluscs). Cyst (Fig. 144) spherical, 0.21-0.25 mm in diameter, commonly found in foot of pelecypods. The metacercaria has
not yet been described but the cercaria and adult, and therefore presumably the metacercaria, bear twenty-nine collar spines arranged in
an unbroken row, with the last lateral ones being slightly smaller and
situated slightly lower than the remainder.
Other information. Lebour (1909) has been able to infect Mytilus
edulis with cercariae emerging from the first intermediate host, Littorina
littorea. Although the other aspects of the life cycle of H . leptosoma
have not been demonstrated, there is no reason to believe that its life
cycle should be different from that of H . quissetensis given below. The
avian definitive host, which is also known to include Tringia aZpina,
T . canutus, Limosa and Arenaria, undoubtedly acquires its infection
by ingesting metacercariae-harboring pelecypods.
25. Himasthla quissetensis Miller and Northrup, 1926. (Fig. 145)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
During a survey of larval trematodes in the mud flat snail, Nassarius
obsoletus, Miller and Northrup (1926) examined 8 875 specimens from
Quamquisset Harbor, Massachusetts, and as the result described a new
echinostome cercaria, Cercaria quissetensis. Subsequently, Stunkard
(1934, 1937, 1938), following successful life cycle studies, has reported
that C. quissetensis is the larva of Himasthla quissetensis, an up until
then undescribed species. Stunkard has demonstrated that cercariae
escaping from Nassarius obsoletus will penetrate and encyst in the
mantle, gills and foot of Mya arenaria, Modiolus modiolus, Mytilus
edulis, Cumingia tellinoides, Aequipecten irradians, Ensis directus and
Crepidula fornicata. Of these, Uzmann (1951), as the result of a survey
in Merrimack Bay, Plum Island Sound, and Annisquam River, Massachusetts, and examination of clams from St. Andrews, New Brunswick,
Canada, has reported that Mya arenaria is a commonly parasitized
second intermediate host in nature. Cheng et al. (1966a) have extended
the list of known second intermediate hosts to include Modiolus
demissus, Mercenaria mercenaria and Tapes semidecussata. In addition,
we have reported the finding of metacercariae in the blood vessels and
heart of experimentally infected Crassostrea virginica and on the gill
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
addition to Arenicola marina and Scrobicularia tenuis plana, and Villot
(1875, 1878) has reported it in 8. tenuis and in isopods.
Description of metacercaria (the stage found in economically
important molluscs). Cyst (Fig. 144) spherical, 0.21-0.25 mm in diameter, commonly found in foot of pelecypods. The metacercaria has
not yet been described but the cercaria and adult, and therefore presumably the metacercaria, bear twenty-nine collar spines arranged in
an unbroken row, with the last lateral ones being slightly smaller and
situated slightly lower than the remainder.
Other information. Lebour (1909) has been able to infect Mytilus
edulis with cercariae emerging from the first intermediate host, Littorina
littorea. Although the other aspects of the life cycle of H . leptosoma
have not been demonstrated, there is no reason to believe that its life
cycle should be different from that of H . quissetensis given below. The
avian definitive host, which is also known to include Tringia aZpina,
T . canutus, Limosa and Arenaria, undoubtedly acquires its infection
by ingesting metacercariae-harboring pelecypods.
25. Himasthla quissetensis Miller and Northrup, 1926. (Fig. 145)
(Superorder Anepitheliocystidia; order Echinostomida; suborder Echinostomata; superfamily Echinostomatoidea; family Echinostomatidae)
During a survey of larval trematodes in the mud flat snail, Nassarius
obsoletus, Miller and Northrup (1926) examined 8 875 specimens from
Quamquisset Harbor, Massachusetts, and as the result described a new
echinostome cercaria, Cercaria quissetensis. Subsequently, Stunkard
(1934, 1937, 1938), following successful life cycle studies, has reported
that C. quissetensis is the larva of Himasthla quissetensis, an up until
then undescribed species. Stunkard has demonstrated that cercariae
escaping from Nassarius obsoletus will penetrate and encyst in the
mantle, gills and foot of Mya arenaria, Modiolus modiolus, Mytilus
edulis, Cumingia tellinoides, Aequipecten irradians, Ensis directus and
Crepidula fornicata. Of these, Uzmann (1951), as the result of a survey
in Merrimack Bay, Plum Island Sound, and Annisquam River, Massachusetts, and examination of clams from St. Andrews, New Brunswick,
Canada, has reported that Mya arenaria is a commonly parasitized
second intermediate host in nature. Cheng et al. (1966a) have extended
the list of known second intermediate hosts to include Modiolus
demissus, Mercenaria mercenaria and Tapes semidecussata. In addition,
we have reported the finding of metacercariae in the blood vessels and
heart of experimentally infected Crassostrea virginica and on the gill