Comparative Parasitology 68(2) 2001 - Peru State College

222 COMPARATIVE PARASITOLOGY, 68(2), JULY 2001
ETYMOLOGY: This species is named for its
type locality, Vietnam.
Remarks
Singhiatrema vietnamensis is consistent with
members of Ommatobrephidae because it has a
preacetabular cirrus sac with an internal seminal
vesicle; large embryonated eggs, with some containing
an oculate miracidium; and opposite incompletely
lobed testes located in the posterior
region of the body, often with axes diverging
anteriorly. The species belongs in Ommatobrephinae
rather than Parorchiinae Lai, 1936, because
the collar of spines is interrupted dorsally
and ventrally as opposed to being arranged in a
continuous row. In addition, the tegument is
smooth rather than spinous, an external seminal
vesicle is absent, spines do not occur on the intromittent
organ, and the specimens are parasites
in reptiles rather than birds. The 2 genera within
Ommatobrephinae, Singhiatrema and Ommatobrephus
Nicoll, 1914, are distinguished by the
presence of a dorsally interrupted row of collar
spines in the former and the absence of the collar
spines in the latter. The presence of a dorsally
and ventrally interrupted row of 22-23 collar
spines in 5. vietnamensis enables us to assign
the worms to the genus Singhiatrema. Singhiatrema
was originally unveiled to science in an
oral presentation and abstract at the Forty-first
Session of the Indian Science Congress (Simha,
1954). The genus was described in more detail
by Simha (1958) and placed in Echinostomatidae
Poche, 1926, by the author without a subfamily
designation. Singhiatrema singhia Simha,
1954, from a colubrid ratsnake (Ptyas mucosus
(Linnaeus, 1758)) from Hyderabad in southern
India, was designated the type species (Simha,
1954). Two other species, Singhiatrema longifurca
Simha, 1958, and Singhiatrema hyderabadensis
Simha, 1958, parasitize another colubrid
water snake, the checkered keelback Xenochrophis
piscator (Schneider, 1799) (as Tropidonotus
piscator}, from the same locality
(Simha, 1958). Three other Indian species have
since been added to the genus. Singhiatrema najai
parasitizes the Indian cobra (N. najd) in Hyderabad,
S. lali parasitizes the turtle H. thurgii
in Lucknow, and Singhiatrema piscatora Dwivedi,
1968, parasitizes the water snake X. piscator
in Chhindwara (Chakrabarti, 1967; Chattopadhyaya,
1967; Dwivedi, 1968).
Singhiatrema vietnamensis differs from its
Copyright © 2011, The Helminthological Society of Washington
congeners, with the exception of S. lali, by having
ceca that extend to the posterior region of
the body and vitelline follicles that lie ventral
and lateral to the ceca in bands stretching from
the posterior margin of the acetabulum to the
midlevel of the testes. Singhiatrema vietnamensis
differs from S. lali by having larger eggs
(103-119 |xm long by 45-56 jxm wide vs. 65-
87 |xm long by 34-39 |xm wide), ceca that reach
beyond the posterior level of the testes rather
than to their midlevel, longer collar spines (31-
56 (Jim rather than 7-9 jxm), and a snake rather
than a turtle definitive host. Yamaguti (1971) reported
24 collar spines for S. lali; however,
Chakrabarti (1967) did not report the number of
collar spines in the description of S. lali, and the
illustration of the species did not permit the collar
spines to be counted. Specimens of S. lali
were apparently never deposited in a lending
museum. We report 22-23 collar spines in our
specimens of 5. vietnamensis. Three of 5 of our
specimens had 22 collar spines and the remaining
2 had 23 collar spines. It is possible that
some specimens could lose spines in life or handling,
but biological variation probably exists.
Initially, we obtained 4 specimens of S. vietnamensis
that had been placed in fresh water
prior to their fixation with slight pressure in unheated
formalin (see Fig. 2). The overall shape
of these specimens, as well as their measurements,
varied dramatically from those specimens
fixed with heat and used in the above description.
Specimens subjected to fresh water and
pressure had an oval rather than pyriform body
shape, and their width was greater (1.0-1.6 mm
vs. 0.75-0.91 mm). The pharynx was swollen
(131-158 |xm long by 127-140 jxm wide vs. 95-
106 (Jim long by 78-106 |xm wide), and the
esophagus was contracted in length but swollen
in width (285-415 (xm long by 77-203 |xm wide
vs. 547-640 (xm long by 80-105 |xm wide). In
addition, the ceca were contracted slightly,
reaching to the posterior level of the testes rather
than beyond the posterior level of the testes, and
the eggs were swollen or collapsed and therefore
larger in whole mounts (109—117 |xm long by
81-95 urn wide vs. 103-119 |xm long by 45-56
(xm wide). The long side of the oval cirrus sac
was oriented laterally rather than vertically, with
the pore on the sinistral end rather than at the
anterior end, and the testes were larger (411-560
|xm long by 258-339 |xm wide compared with
250-340 |xm long by 195-234 |xm wide). If the