An illustrated description of five new tardigrade species belonging to genus Milnesium is given. The new species differ from all known species of this genus mainly by the proportions of the claws and bucco-pharyngeal apparatus. A new key to the determination of recent species of the genus Milnesium is presented.

Pseudechiniscus, the second-largest genus of the family Echiniscidae (Tardigrada: Heterotardigrada: Echiniscoidea), is notoriously difficult for taxonomic studies. In this study, I performed a morphological analysis of a new species from Croatia, based on a light microscopic and scanning electron microscopic examination of 45 specimens from the same sample. Furthermore, I have summarized all available data on Pseudechiniscus species, including their original descriptions, and have analysed the following complexes of morphological characters: (1) arrangement and morphology of dorsal cuticular plates, (2) ventral sculpture, (3) morphology of cephalic, trunk and leg sensory organs and (4) claw morphology. The applicability of these characters in the taxonomy and their distribution in the genus are discussed. Some of the characters traditionally used for species delimitation were shown to be unsuitable and others in need of a thorough reinvestigation. The meaning of the old term ‘faceted’, commonly used but often misapplied, has been clarified, based on the initial definition. Several characters of the claw structure were suggested as potentially useful for species delimitation. The taxonomic status of several old forms and species was discussed.

ABSTRACT

An illustrated description of Macrobiotus barabanovi sp. nov. and Macrobiotus kirghizicus sp. nov. from Tien Shan (Kirghizia) is given. Macrobiotus barabanovi sp. nov. belongs to the harmsworthi group. It differs from the majority of species of this group in having very long claws. Macrobiotus kirghizicus sp. nov. is similar to M. ariekammensis in claw morphology, but differs clearly from this species in having differences in bucco-pharyngeal apparatus and characters of the egg processes. Based on the details of the claws structure, M. ariekammensis is excluded from the tenuis group of the genus Macrobiotus and grouped together with M. kirghizicus sp. nov. in the new ariekammensis group.

An integrative redescription of Hypsibius pallidoides Pilato, Kiosya, Lisi, Inshina & Biserov, 2011 was undertaken following a reexamination of the type material and new material using high-quality light microscopy, scanning electron microscopy and methods of molecular taxonomy. Detailed morphological investigations revealed a unique complex of characters that precluded the attribution of this species to the genus Hypsibius Ehrenberg, 1848. Furthermore, phylogenetic analyses indicated the affinity of this species within the subfamily Pilatobiinae (Hypsibiidae). Notahypsibius gen. nov. is erected for H. pallidoides and two putatively related species: H. scaber Maucci, 1987 and Ramazzottius arcticus (Murray, 1907). An emended diagnosis for the genus Pilatobius is given, while the subfamily Pilatobiinae lacks a cohesive morphological diagnosis despite representing, at the same time, a well-supported molecular clade. Obvious controversy between the results of the morphological and molecular analyses of the phylogeny of Hypsibioidea is discussed. The distribution of morphological characters such as the claw type, organization of the bucco-pharyngeal apparatus, and egg shell sculpture type within Eutardigrada is analyzed and their phylogenetic significance discussed.