An integrative revision of <i>Mesocrista</i> Pilato, 1987 (Tardigrada: Eutardigrada: Hypsibiidae)

<i>Mesocrista</i> is a Holarctic tardigrade genus currently classified within the subfamily Itaquasconinae (Eutardigrada: Parachela: Hypsibiidae). The position of the genus has been so far inferred solely on the basis of light microscopy observations. Here, we present the first-ever scanning electron microscopy images of a dissected bucco-pharyngeal apparatus and DNA sequences for <i>Mesocrista</i> from Spitsbergen, mainland Norway and Poland. The new data allowed an integrative redescription of the nominal <i>M. spitzbergensis</i> from the <i>locus typicus</i> and uncovered a new species, <i>M. revelata</i>, from the European localities. The two species differ phenotypically by the oral cavity armature and claw morphology as well as by a number of morphometric traits, and they are also distinct genetically in all sequenced DNA markers, three nuclear (18S rRNA, 28S rRNA, ITS-2) and one mitochondrial (COI). Both molecular and morphometric data presented in this paper suggest that previous records of <i>M. spitzbergensis</i> should be treated with caution, since most probably some of them signify different <i>Mesocrista</i> species. Our phylogenetic analysis confirmed that <i>Mesocrista</i> is indeed a member of the Itaquasconinae. We also found that the most closely related, among genera for which there are molecular data available, is <i>Adropion</i>, from which <i>Mesocrista</i> differs by the shape of the apophyses for insertion of stylet muscles and the width of the bucco-pharyngeal tube. Finally, we advocate that <i>Diphascon marcusi</i>, a rare species hypothesised to represent either <i>Mesocrista</i> or <i>Adropion</i>, should be transferred to the latter genus and that the species should be redescribed to confirm its validity and systematic position. http://zoobank.org/urn:lsid:zoobank.org:pub:6515D58D-8469-4854-8687-177232112BDA