Comparative Parasitology 68(2) 2001 - Peru State College

226 COMPARATIVE PARASITOLOGY, 68(2), JULY 2001
vitellarium can be used as an informative generic
level taxonomic distinction.
Fixation techniques
A wide variety of techniques has been used
by parasitologists to fix specimens. Most of
those techniques yield satisfactory and consistent
results; however, those that produce results
inconsistent with other procedures should be
avoided. We advocate collecting digeneans by
initially placing them live in physiological saline
solution (7.7—8.5 g NaCl per liter of distilled water).
They should never be exposed to distilled
or tap water while alive. Unless specimens are
to be used for ultrastructural or other specific
puiposes, they should be killed rapidly with
heat. They can be killed by a flame under a slide
with worms in a small amount of saline or by
pouring a relatively large volume of hot or boiling
saline or tap water over specimens immersed
in little or no saline. The specimens then should
be transferred, without touching them with forceps,
into 5—10% buffered formalin solution
soon after being killed. Killing with hot formalin
solution or other fixatives is acceptable but produces
harsh fumes. Killing with heat produces
consistently fixed specimens, ideal for making
comparative measurements. Fixation with pressure
may be useful for examining certain organ
systems such as the female reproductive complex
or the terminal genitalia, but specimens
fixed under pressure should be used with care
for taxonomic purposes because the entire specimen
or specific structures may be distorted.
Comparison of heat-killed specimens with
specimens bathed in fresh water and then coldkilled
revealed differences. Specimens of S. vietnamensis
that were osmotically stressed prior to
fixation were a different shape, they were wider,
the pharynx and esophagus were distorted, the
ceca were slightly shorter, the testes were larger,
and the cirrus sac was oriented differently. Any
one of these conditions might be used to misidentify
a species, incorrectly describe specimens,
or provide misleading information.
Stressed specimens of 5. taiwanensis exhibited
some distortions at the specific level, but more
importantly, the confluent vitelline follicles represent
a generic distinction for Gogatea. Lack of
knowledge about the methods used on specimens
for descriptions of some species of Gogatea
and Szidatia shows the need to reevaluate
those species with heat-killed specimens. Until
Copyright © 2011, The Helminthological Society of Washington
such material is available, we prefer to treat the
genera separately.
Acknowledgments
We thank Cathy Schloss and Kristine Wilkie
of the Gulf Coast Research Laboratory for helping
with some of the literature. We also thank
Eric Hoberg and Pat Pilitt from the United States
National Parasite Collection, Beltsville, Maryland,
for the loan of a specimen and Dr. Richard
Heckmann of Brigham Young University for his
interest in the project. Partial support for this
study was provided by International Paper.
Literature Cited
Chakrabarti, K. K. 1967. On a new echinostome
(Singhiatrema lali n. sp.) from the intestine of a
turtle. Science and Culture 33:407-408.
Chattopadhyaya, D. R. 1967. On a new trematode of
the genus Singhiatrema Simha, 1954, from the
cloaca of the Indian cobra in Hyderabad. Indian
Journal of Helminthology 18:45-49.
Dollfus, R. P. 1953. Miscellanea helminthologica
Maroccana VII. Les Szidatia de Matrix viperina
(Latreille, 1802) [Trematoda Digenea]. Archives
de 1'Institut Pasteur du Maroc 4:505-512.
Dubois, G. 1938. Monographic des Strigeida (Trematoda).
Memoires de la Societe Neuchateloise des
Sciences Naturelles 6:1—535.
. 1951. Nouvelle cle de determination des groupes
systematiques et des genres de Strigeida
Poche (Trematoda). Revue Suisse de Zoologie
58(39):639-691.
-. 1953. Liste Systcmatique des Strigeida (Trematoda)
de 1'Inde. Pages 77-88 in J. Dayal and K.
Singh, eds. Thapar, G. S., Commemoration Volume.
University of Lucknow, Lucknow, India.
Dwivedi, M. P. 1968. On a new species of the genus
Singhiatrema Simha, 1954 (Trematoda: Echinostomidae).
Indian Journal of Helminthology 19:
141-144.
Fischthal, J. H., and R. E. Kuntz. 1975. Some trernatodes
of amphibians and reptiles from Taiwan.
Proceedings of the Helminthological Society of
Washington 42:1-13.
Hughes, R. C. 1929. Studies on the trematode family
Strigeidae (Holostomidae) No. XIV. Two new species
of diplostomula. Occasional Papers of the
Museum of Zoology, University of Michigan 202:
1-29 + 1 pi.
Joyeux, C., and J. G. Baer. 1934. Sur un trematode
de couleuvre. Revue Suisse de Zoologie 41:203-
215.
Langeron, M. 1924. Recherches sur les cercaires des
piscines de Gafsa et enquete sur la bilharziose
Tunisienne. Archives de FInstitut Pasteur de Tunis
13:19-67.
Lutz, A. 1935. Observances e consideracoes sobre
Cyathocotylineas e Prohemistomineas. Memorias
do Institute Oswaldo Cruz 30:157-182.
Mehra, H. R. 1947. Studies on the family Cyathoco-