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Together, Indian plus Seychelles caeciliid caecilian amphibians (Gymnophiona) constitute approximately 10% of the extant species of this order. A molecular phylogenetic analysis of all but one (or two) nominal species (16, in five genera) is presented based on mitochondrial (12S, 16S, cytb, cox1) and nuclear (RAG1) sequence data. Results strongly support monophyly of both Seychelles and peninsular Indian caeciliids, and their sister-group status. Within the Indian caeciliids, Indotyphlus and Gegeneophis are monophyletic sister genera. The phylogenetic position of Gegeneophis ramaswamii, Gegeneophis seshachari, and Gegeneophis carnosus are not well resolved, but all lie outside a well-supported clade of most northern Western Ghats Gegeneophis (madhavai, mhadeiensis, goaensis, danieli/nadkarnii). Most nominal species of Indian caeciliid are diagnosed by robust haplotype clades, though the systematics of G. carnosus-like forms in northern Kerala and southern Karnataka requires substantial further investigation. For the most part, Indian caeciliid species comprise narrowly distributed, allopatric taxa with low genetic diversity. Much greater geographic genetic diversity exists among populations referred to G. seshachari, such that some populations likely represent undescribed species. This, the first phylogenetic analysis of Indian caeciliids, generally provides additional support for recent increases in described species (eight since 1999), and a framework for ongoing taxonomic revision.

Morphological evidence suggests harpacticoid copepods have recurrently entered into symbiosis with other crustaceans but only members of the family Cancrincolidae have successfully made the transition from marine habitats to semiterrestrial hosts. Cancrincolids are primarily amphi-Atlantic in distribution (with one outlier in the western Pacific) and typically inhabit the gill chambers of grapsoidean land crabs belonging to the families Grapsidae, Sesarmidae, Varunidae and Gecarcinidae. Morphologically, they are difficult to place because they exhibit unusual autapomorphies and the shared derived characters claimed to unite them with the primitively marine Ameiridae are equivocal. Both maximum parsimony and Bayesian inference solutions based on SSU rDNA gene sequences show topological congruence in placing the Cancrincolidae within the Ameiridae and in firmly resolving it as the sistergroup of taxa that have been reported as obligate or commensal associates of crayfish. This relationship is further supported by swimming leg sexual dimorphism and mandibular palp morphology. Morphological comparison with ameirid copepods revealed the majority of synapomorphies previously proposed in support of cancrincolid monophyly and familial distinctiveness can be attributed to heterochrony. The progressive evolution of cancrincolid associates appears to be largely concordant with the sequential adaptation to terrestriality by their grapsoidean hosts. The current amphi-Atlantic distribution of Cancrincola may suggest its possibly free-living ancestor had already assumed a virtually continuous distribution along the northern seaboard of Gondwana prior to the opening of the South Atlantic during the early Cretaceous, implying symbiotic relationships were established only much later when grapsoidean crabs started to emerge, radiate and diversify in the mid-Tertiary (15–35 mya). The adoption of semi-terrestriality in cancrincolid copepods can be viewed as yet another independent attempt (incursion) to colonize low-salinity environments by members of the family Ameiridae. The possible sistergroup relationships of the Ameiridae and the position of the genus Argestigens Willey are discussed.