Under the lens: disclosing the Echiniscus lentiferus complex (Heterotardigrada), caudal plate bulge-bearing Australian endemics

The vast majority of knowledge on Australian tardigrades has its roots in the PhD thesis by Sandra Claxton from 2004. More than a decade later, one of the more spectacular species documented in the dissertation was described as Echiniscus lentiferus from Tasmania. The species is unique among all Echiniscidae in possessing a lens-shaped, strongly opalescent swelling in the middle of the caudal plate. We analysed Echiniscus populations exhibiting the caudal bulge from numerous localities in Victoria and Tasmania. A set of standard integrated morphological (light and scanning electron microscopy, morphometry, and statistics) and molecular (DNA barcoding) methods was applied. As a result, Echiniscus lentiferoides sp. nov. is described based on material from several localities. The morphological observations of numerous populations confirmed what was previously shown for E. lentiferus, i.e. a rather weak sexual dimorphism, a state rather atypical for Australian echiniscids. At the same time, a large variability in the development of the caudal bulge was detected, a findinng that is in contrast to Claxton’s reports. By delivering genetic data to supplement the highly scarce molecular dataset of Australian tardigrades, the complex was located in the Echiniscus phylogenetic tree, contributing to a better comprehension of the generic historical biogeography. Our results indicate the high importance of the Nothofagus cool temperate rainforests and mesic habitats for preserving distinctive Australian endemics. The E. lentiferus complex is likely restricted only to Victoria and Tasmania, since sampling in similar habitats in New South Wales and Queensland did not yield any representatives of this group.