Shape of the Spermathecal Atrial Glands: A Novel Taxonomic Character to Distinguish Earthworm Species of the Genus <i>Moniligaster</i> Perrier, 1872 (Clitellata, Moniligastridae)

The order Moniligastrida Brinkhurst & Jamieson, 1971, comprises a large and diverse group of terrestrial megadrile worms with a single nominate family Moniligastridae Claus, 1880. They are considered as the most primitive group among the earthworms. Being primitive, certain classical characters such as dimension, extent of clitellum, shape of the testis sacs, shape of the prostate when it is glandular, number of gizzards etc. have little systematic importance in moniligastrids. Consequently, moniligastrids are taxonomically complex and challenging with regard to their identification. For the identification of moniligastrids, all the characteristics related to prostate (shape of the prostate and prostatic capsule, segmental location, entry point of vas into the prostate, etc.) and spermathecal atrium (shape, segmental location, etc.) are required to be elaborated, whereas remaining features only have supportive roles. At present, 5 genera comprising 176 species are recognised in this family. Among these, Moniligaster Perrier, 1872 is the second largest genus with 14 species, which is endemic to southern Western Ghats with one record from Eastern Ghats of south-western Peninsular India. In Moniligaster genus, atrial glands are associated with spermatheca, glands branched in a more or less regularly dichotomous fashion, the branches and terminal tubules closely compacted into a shape with mammillated surface. Former pioneers have not detailed about the size and shape of the spermathecal atrial glands as a taxonomical character. Here, we have recognised the size and shape of the spermathecal atrial glands as an additional taxonomic character to distinguish all the known Moniligaster species based on the collections of 12 out of 14 species from several areas of the Western Ghats of Kerala state. Other two species data were gathered from the published literature. The description of the spermathecal atrial glands of each species provided in this article will serve as a baseline database for distinguishing various Moniligaster species.