Summary

As a part of the ongoing biodiversity survey of aseptate gregarines in earthworms, samplings were carried out in the Murshidabad district of the state of West Bengal (India). The survey revealed a new species of the genus Monocystis Stein, 1848, M. septum sp. n., in the earthworm host Eutyphoeus orientalis (Beddard). The gamonts of M. septum are rectangular, slightly tapering towards the anterior and the posterior end. The unique feature of the gamonts is the presence of a constriction at the anterior body end that tends to divide the cell into two parts, similarly to septate gregarines. The gamonts measure 86.3-102.3 µm (90.4 ± 4.2, 36) in length and 66.1-89.3 µm (78.2 ± 0.9, 36) in width. The gametocyst consists of two gametocytes of unequal size and peculiar shape: one is axe-like, the other semicircular. The gametocysts measure 46.1-78.6 µm (64.2±1.2, 36) in length and 39.7-68.4 (62.4±1.8, 36) in width. Bi-conical oocysts measure 6.4-9.3 µm (8.2±0.9, 36) in length and 5.5-7.6 µm (6.1±2.1, 36) in width. Key words: gregarines, earthworm, seminal vesicles, systematics, Monocystis septum sp. n. have been reported. Out of them, 13 species have been reported from oligochaete hosts. The pros-pects of finding new gregarine species from the new earthworm hosts are immense. Only a few of over 350 species of Indian earth-worms have been studied for the occurrence of gregarines, but this research has gained momentum since the 1980ies. It has already resulted in the finding of representatives of the genera Apolocysti