An integrative revision of Mesocrista Pilato, 1987 (Tardigrada: Eutardigrada: Hypsibiidae)

ABSTRACT

Mesocrista 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 Mesocrista from Spitsbergen, mainland Norway and Poland. The new data allowed an integrative redescription of the nominal M. spitzbergensis from the locus typicus and uncovered a new species, M. revelata, 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 M. spitzbergensis should be treated with caution, since most probably some of them signify different Mesocrista species. Our phylogenetic analysis confirmed that Mesocrista 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 Adropion, from which Mesocrista differs by the shape of the apophyses for insertion of stylet muscles and the width of the bucco-pharyngeal tube. Finally, we advocate that Diphascon marcusi, a rare species hypothesised to represent either Mesocrista or Adropion, 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

KEYWORDS:

• 18S rRNA
• 28S rRNA
• Adropion marcusi comb. nov.
• AISM
• Arctic
• biodiversity
• bucco-pharyngeal apparatus extraction protocol
• COI
• Hypsibiidae
• Itaquasconinae
• ITS-2
• Mesocrista revelata sp. nov.
• M. spitzbergensis
• Svalbard

Acknowledgements

We would like to thank Genowefa and Maja Przybycień for moss samples from Kamienna Góra and for their for help in the hunt for A. marcusi. We also acknowledge Wojciech and Kasper Hlebowicz for moss samples from Tromsø, and Henryk Marszałek (University of Wrocław) for soil samples from Hyttevika. ŁM is grateful to Jette Eibye-Jacobsen (University of Copenhagen, Denmark) who demonstrated the sodium hypochlorite extraction method to him during his scientific visit to the Natural History Museum in Copenhagen.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Foundation for Polish Science [HP/2012-5/8 to ŁM]; European Regional Development Fund [POIG.02.01.00-12-023/08 to the Jagiellonian University]. European Commission’s (FP 6) Integrated Infrastructure Initiative SYNTHESYS [DK-TAF-2510 to ŁM]; Ministry of Science and Higher Education of the Republic of Poland [DI2011 035241 to KZ].