PETASIGER OSCHMARINI N. SP. (DIGENEA, ECHINOSTOMATIDAE) IN THE GREBESPODICEPS GRISEGENA (BOD.) AND P-AURITUS (L.) (AVES, PODICIPEDIDAE) FROM KAMCHATKA, RUSSIA

A re-examination of three sets of trematodes collected in two species of grebes, Podiceps grisegena and P. auritus, from the Kamchatka regio n of eastern Russia, previously identified as Petasiger neocomense, re vealed that they actually represent a new species, which is named Peta siger oschmarini. Characteristic morphological features of the new spe cies include: a head collar possessing a constant number of 19 spines; a large cirrus-sac comparable in size to the ventral sucker, containi ng a bipartite seminal vesicle and a well-developed pars prostatica; a large bulb-like cirrus similar in size to the testes; a long forebody ; a long oesophagus; testes situated obliquely or symmetrically; and l ateral vitelline fields which are not confluent in the forebody. The n ew species is distinguished from all Palaearctic and Nearctic members of Petasiger, which possess 19 collar spines. The material described b y Oschmarin (1950) as P. neocomense is considered to be conspecific.