Indobathynella prehensilis n. gen., n. sp., an Aberrant Species of Bathynellacea (Eumalacostraca) from India

Abstract

A B S T R A C TA new bathynellacean, Indobathynella prehensilis n. gen., n. sp., is described from farm bores in southeastern India. This is an aberrant species, possessing such a unique combination of plesiomorphic and apomorphic characters that it cannot be assigned outright to any of the three known families of the order Bathynellacea, viz., Bathynellidae, Parabathynellidae, and Leptobathynellidae. And yet, it is provisionally placed in Bathynellidae pending reconstruction of the phylogenetic relationships within Bathynellacea. This decision is based mainly on the following plesiomorphies: 1) antennule is 7-segmented; 2) antenna has exopodal segment; 3) mandibular palp is 3-segmented; and 4) male thoracopod VIII has a basal penile lobe. The new taxon also displays some close apomorphic affinities with Parabathynellidae such as a 3-segmented prehensile maxilla, a lobe-like female thoracopod VIII, and a 1-segmented pleopod I. The other spectacular apomorphies of the new species, some of them suggesting its possible neotenic origin, are unique to Bathynellacea as a whole, and these include: 1) antenna is 4-segmented, with extremely reduced armature; 2) gnathobase consisting of 5 distinct teeth is fused with the first segment of mandibular palp; 3) thoracopods I-VII have 2-segmented exo-and endopod, except for 3-segmented endopod on thoracopod I, and with only a single endopodal seta on thoracopods II-VII; and 4) male thoracopod VIII is greatly reduced and uncinate, with exopod being fused with basis and having only two setae. All in all, the new taxon seems to be a crucial phylogenetic link between Bathynellidae and Parabathynellidae. A note on the ecology and biogeography of the new species is also added.