6. THE PHYLA PORIFERA, CNIDARIA A N D PLATYHELMINTHES
207
Louisiana. It was most probably this species that Tennent (1905, 1906,
1909) found in C. virginica taken from the Rappahannock River in
Virginia and a t Beaufort, North Carolina, although he designated his
specimens as B. haimeanus. Although B. cuculus is extremely difficult
to distinguish from B. haimeanus morphologically, I am in agreement
with Hopkins (1954a) that : “ it would be very difficult to believe that
two forms with such striking ecological and physiological differences
could belong to one species.” B. haimeanus is found in molluscs in
waters of high salinity, while B. cuculus is confined to the least saline
parts of the range of Crassostrea virginica.
Description of stages in mollusc. The tubular and dendritic sporocysts
of B. cuculus are extremely similar to those of B. haimeanus (Fig. 113).
Tennent (1906), under the name B. haimeanus, has given a good
description of the developing stages of the sporocyst of B. cuculus.
The most characteristic features of the sporocyst are that its diameter
is rather uniform, measuring 0.1 mm, and the growing end is rounded
and somewhat greater in diameter than the older portions (Fig. 112).
The following description of the cercaria is based on the descriptions
given by Tennent (1906) and Hopkins (1954a).
Cercaria (Fig. 114) with characteristic forked tail, with each furca
measuring 0-04-0.20 mm long x 0.07-0.17 mm wide in contracted
state, it may be as long as 5-10 mm when extended ; each furca attached
to globose, more or less bilobed stem a t its anteroventral borders ; body
proper elongate, 0.15-0.40 mm long x 0-04-0.12 mm wide, covered
with cuticular spines anteriorly ; mouth a t middle of body, surrounded
by ventral sucker which measures 0.026-0.029 mm in diameter ; mouth
leads into simple blind sac caecum ; anterior holdfast (rhynchus)
surrounded with gland cells as is ventral sucker ; genital anlagen
posterior to pharynx and intestine ; subcuticular glands opaque,
scattered over entire body surface, also along posterior edge of tail
stem and furcae; flame-cell pattern 2[2 + 2 + 2) + (2 + 2 + a)].
Life cycle. Tennent (1906) has reported what he assumed to be the
life cycle of B. cuculus (referred to by him as B. haimeanus). He
reported the finding of encysted metacercariae in the silverside, Menidia
menidia, and adults in the intestine of Strongylura marina. Thus the
life cycle is similar in pattern to what has been assumed for B. haimeanus.
Hopkins (1954a), however, has correctly pointed out that Tennent has
not proven beyond doubt that there is any connection between B.
cuculus from Crassostrea virginica and the stages found in Menidia and
Xtrongylura. Furthermore, as the result of examining bucephalid
trematodes in these two species of fish, Hopkins has convincingly
207
Louisiana. It was most probably this species that Tennent (1905, 1906,
1909) found in C. virginica taken from the Rappahannock River in
Virginia and a t Beaufort, North Carolina, although he designated his
specimens as B. haimeanus. Although B. cuculus is extremely difficult
to distinguish from B. haimeanus morphologically, I am in agreement
with Hopkins (1954a) that : “ it would be very difficult to believe that
two forms with such striking ecological and physiological differences
could belong to one species.” B. haimeanus is found in molluscs in
waters of high salinity, while B. cuculus is confined to the least saline
parts of the range of Crassostrea virginica.
Description of stages in mollusc. The tubular and dendritic sporocysts
of B. cuculus are extremely similar to those of B. haimeanus (Fig. 113).
Tennent (1906), under the name B. haimeanus, has given a good
description of the developing stages of the sporocyst of B. cuculus.
The most characteristic features of the sporocyst are that its diameter
is rather uniform, measuring 0.1 mm, and the growing end is rounded
and somewhat greater in diameter than the older portions (Fig. 112).
The following description of the cercaria is based on the descriptions
given by Tennent (1906) and Hopkins (1954a).
Cercaria (Fig. 114) with characteristic forked tail, with each furca
measuring 0-04-0.20 mm long x 0.07-0.17 mm wide in contracted
state, it may be as long as 5-10 mm when extended ; each furca attached
to globose, more or less bilobed stem a t its anteroventral borders ; body
proper elongate, 0.15-0.40 mm long x 0-04-0.12 mm wide, covered
with cuticular spines anteriorly ; mouth a t middle of body, surrounded
by ventral sucker which measures 0.026-0.029 mm in diameter ; mouth
leads into simple blind sac caecum ; anterior holdfast (rhynchus)
surrounded with gland cells as is ventral sucker ; genital anlagen
posterior to pharynx and intestine ; subcuticular glands opaque,
scattered over entire body surface, also along posterior edge of tail
stem and furcae; flame-cell pattern 2[2 + 2 + 2) + (2 + 2 + a)].
Life cycle. Tennent (1906) has reported what he assumed to be the
life cycle of B. cuculus (referred to by him as B. haimeanus). He
reported the finding of encysted metacercariae in the silverside, Menidia
menidia, and adults in the intestine of Strongylura marina. Thus the
life cycle is similar in pattern to what has been assumed for B. haimeanus.
Hopkins (1954a), however, has correctly pointed out that Tennent has
not proven beyond doubt that there is any connection between B.
cuculus from Crassostrea virginica and the stages found in Menidia and
Xtrongylura. Furthermore, as the result of examining bucephalid
trematodes in these two species of fish, Hopkins has convincingly