Abstract
Tardigrade research in Japan dates back over 100 years, and to date, 167 species of this ecdysozoan phylum have been reported from the country. Of these species, the Macrobiotus hufelandi complex has been represented only by the nominal taxon of this group, Macrobiotus hufelandi. In this article, a new species of the hufelandi group from Japan, Macrobiotus shonaicus sp. nov., is described using integrative taxonomy. In addition to the detailed morphological and morphometric data, obtained using phase contrast light microscopy (PCM) and scanning electron microscopy (SEM), we provide DNA sequences of four molecular markers (both nuclear and mitochondrial). The new species belongs to the persimilis subgroup and is most similar to M. anemone from USA, M. naskreckii from Mozambique, and M. patagonicus from Argentina, but it can be easily distinguished from these species by the presence of thin flexible filaments on terminal discs of the egg process. By the latter character, the new species is most similar to M. paulinae and M. polypiformis, but it can be easily distinguished from them by having a solid egg surface between egg processes (i.e., without pores or reticulum). A phylogenetic analysis of available DNA sequences of the COI marker for the hufelandi group revealed that the new species clusters with the two other species that exhibit filaments on egg process discs (M. paulinae and M. polypiformis) and with two species that have entire egg processes modified into filaments (M. kristenseni and M. scoticus). All five species form a clade distinct from all other sequenced species of the hufelandi group with typical mushroom- or inverted goblet-shaped egg processes, which may suggest that the ancestor of the five species with atypical egg processes had a mutation allowing derivations from the mushroom or inverted chalice-like shape of egg processes.
Highlights
Terrestrial tardigrades are micrometazoans most commonly found in mosses, lichens, leaf litter and soil [1]
The new species belongs to the persimilis subgroup, but it has modified egg processes with some teeth of terminal discs elongated to flexible filaments, such as those found in two other recently described species: Macrobiotus paulinae Stec, Smolak, Kaczmarek & Michalczyk, 2015 [11] from Africa and Macrobiotus polypiformis Roszkowska, Ostrowska, Stec, Janko & Kaczmarek, 2017 [12] from South America
The new species can be distinguished from both species by having a solid egg surface between processes instead of the surface covered by the reticulum, a cuticular fold on the internal surface of legs I–III, smaller pores, a different morphology of the ventral teeth in the third band under phase contrast light microscopy (PCM), and by the presence of a subterminal constriction in the second macroplacoid
Summary
Terrestrial tardigrades are micrometazoans most commonly found in mosses, lichens, leaf litter and soil [1].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
