Dr. Murai Éva szerk.: Parasitologia Hungarica 16. (Budapest, 1983)

Key to genera of Opisthodiscinae 1. Testes at the same zone, vitellaria along caeca, accessory sucker present . Opisthodiscus - Testes tandem or obliquely tandem, vitellaria at posterior part of caeca, central prominence present Megalodiscus Opisthodiscus Cohn, 1904 Diagnosis. Opisthodiscinae. Body cylindrical or pyriform. Primary pharyngeal sacs well developed. Pharynx Microrchis-type. Oesophagus short, bulb present. Caeca terminating at base of acetabulum, more or less arch-shaped. Two testes, preovarian, at the same zone; cirrus pouch present at primary pharyngeal sacs. Genital opening in front of bifurcation, Subclavatus-type. Ovary in acetabular or preacetabular zone, uterus intercoecal, anteriorly extracoecal. Egg numerous, embryonated. Vitellaria lateral between posterior end of pharynx and caecal ends. Acetabulum large, ventroterminal with accessory sucker. Parasitic in rectum of amphibians. Type and single species: Opisthodiscus diplodiscoides Cohn, 1904 (Fig. 26) Megalodiscus Chandler, 1923 Syn.: Pseudopisthodiscus Yamaguti, 1958 Before designation of the genus, in which the North American amphibian amphistomes were involved, Diplodiscus temperatus was already known (STAFFORD, 1905). At that time the characters of the genus Diplodiscus and Megalodiscus (the former one having one the latter two testes) were regarded to be specific rather than generic taxonomic feature. Therefore the validity of CHANDLER' s genus was questioned (CHAPIN, 1926; CORT, 1926; HUNTER, 1930) but HARWOOD (1932) pointed out the fundamental differences which distinguish the two genera in question. MILLZNER (1924) described M. ranophilus which was synonymized with M. temperatus by CHAPIN (1926). HOLL (1928) described the species, Opisthodiscus americanus for which YAMAGUTI (1958) created the genus Pseudopisthodiscus. BRAVO-HOLLIS (1941) described M. rankini from the same host (Triturus viridescens) as that of HOLL'

s O. americanus

. In the discussion, however, she did not compare her species with that of HOLL's. The correct systematic position of this species was clarified by BROOKS and FUSCO (1978). They pointed out: as BRAVO-HOLLIS* s species, M. rankini was recovered in the same host as O. americanus

, and as these two species are congeneric, the former should be transferred to the genus Megalodiscus. The type species of this genus, however, is M. americanus CHANDLER, 1923 thus, the name designated by HOLL (1928) is a junior synonym and BRAVOHOLLIS' s name is correct. SOKOLOFF and CABALLERO (1933), on the basis of Mexican material, described M. tem- peratus which was examined by TRAVASSOS (1934) who found that it represents a new species and was described under the name M. montezumae TRAVASSOS, 1934. MANTER (1938) was of the opinion that M. ranophilus MILLZNER, 1924; M. americanus (HOLL, 1928) and M. montezumae TRAVASSOS. 1934 are synonymous with M. temperatus. The writer shares MANTER's opinion on the basis of study of species available and the relevant literature data. Accordingly, the following species are regarded to be valid: M. americanus Chandler, 1923 M. temperatus (Staff

ord, 1905) Syns: M. ranophilus Millzner, 1924 M. montezumae Travassos, 1934 Opisthodiscus americanus Holl, 1928 Pseudopisthodiscus americanus (Holl, 1928)