Diplodinium flabellum: Occurrence and Numbers in the Rumen of Sheep With a Description of Two New Subspecies*

SYNOPSIS. Diplodinium flabellum, previously described on the basis of its occurrence in rumen contents from 3 hosts of Bos indicus, has been observed in domestic sheep. Numbers of this species were quite high, constituting up to 18.8% of the total fauna in one instance. Diurnal changes in numbers for sheep fed once daily were similar to the cycles reported for other Ophryoscolecids. No obvious relationship was found between the occurrence and numbers of D. flabellum and other genera of rumen ciliates. Two new morphologically distinct forms of this species were observed, one without any spines on the posterior left side and one with a single spine. This is in contrast to the original species description in which 2 spines occur on the posterior left side. Intermediate forms were observed which connected the 3 morphological types, indicating their conspecific relationship. It is proposed that the species description for Diplodinium flabellum be emended to include a total of 3 subspecies: Diplodinium flabellum Kofoid and MacLennan, 1932 flabellum subsp. n.; Diplodinium flabellum aspinatum subsp. n.; and Diplodinium flabellum monospinatum subsp. n. Considerable variation in the shape and length of the caudal fan was observed in specimens of the subspecies aspinatum. In three of the four sheep studied, the subspecies aspinatum predominated, while the species monospinatum was highest in the fourth animal. D. flabellum flabellum occurred in very low numbers, ranging from 0 to 2.5% of the total species number.