A comparative account of the embryonic lineage and gonad development in two species of Rhabditidae (Nematoda)

ABSTRACT Nematodes serve as excellent models for developmental studies, with a good number of favourable properties. The family Rhabditidae is a paraphyletic group of bacterivorous nematodes showing diversity in the structure of gonads, mode of reproduction, cleavage pattern, etc. In the present paper, two species of Rhabditidae, namely Mesorhabditis paucipapillata Paetzold, 1955 and Cephaloboides anisospiculus Tahseen et al., 2017, with monodelphic and didelphic types of gonads, respectively, were selected for a comparative analysis of the embryonic patterns and trends in gonad development. The cleavage patterns of the early cell lineages were observed to vary considerably with the division of EMS after three consecutive divisions in the AB line in C. anisospiculus. The patterns of gonad development differed, with the number of branches being the key factor in determining the shape and orientation of the primordium; in contrast, vulva formation largely depended on the position and shape of the vulval opening.