科研之友
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摘要
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.
- 出版日期2016
