An integrative redescription of the nominal taxon for the Mesobiotus harmsworthi group (Tardigrada: Macrobiotidae) leads to descriptions of two new Mesobiotus species from Arctic

Abstract

The Mesobiotus harmsworthi group has a global distribution, with localities in polar, temperate and tropical zones. Since the first species of the harmsworthi group was described in the beginning of the 20th century, tens of new species within the group were found and named. However, the diagnosis of the nominal Mesobiotus harmsworthi is insufficient and enigmatic, thus it can be is a serious obstacle in solving the taxonomy of this group. Here, we integratively redescribe the nominal species for the genus Mesobiotus, i.e., Mesobiotus harmsworthi and clarify taxonomic statuses of the two subspecies: M. harmsworthi harmsworthi and M. harmsworthi obscurus that have been recognised as distinct taxa for more than three decades. Traditionally, egg chorion in M. harmsworthi was considered almost smooth and without any traces of areolation, however here we report many misunderstandings that accumulated across decades and we show that, in fact, the chorion in this species exhibits a partially developed areolation. We present an integrative (morphological, morphometric and molecular) diagnosis of the nominal taxon and we confirm that it differs from other species of the harmsworthi group by morphological characters of both animals and eggs. Additionally, we describe two new species of the genus Mesobiotus: M. skorackii sp. nov. from the Kyrgyz Republic (using classical morphological description) and M. occultatus sp. nov. from Svalbard Archipelago (by means of integrative taxonomy). Finally, we also provide the first genetic phylogeny of the genus Mesobiotus based on COI sequences which, together with molecular species delimitation, independently confirms the validity of the analysed taxa.

The terrestrial invertebrate fauna of Edgeøya, Svalbard: Arctic landscape community composition reflects biogeography patterns

“…The use of additional sampling methodologies such as pitfall traps, sticky traps or water traps for highly mobile and flying invertebrates, are needed to obtain a more complete picture on the invertebrate fauna of Edgeøya. In addition, the use of innovative DNA techniques (Ekrem et al 2018;Søli et al 2018) along with integrative approaches (Kaczmarek et al 2018) and planned monitoring campaigns (Gillespie et al 2018) are required to fully documented biodiversity in the Arctic.…”

First records of tardigrades (Tardigrada) from Irish and Scottish leaf litter

“…While some molecular data are available for the Diphascon pingue, Ramazzottius oberhaeuseri, Macrobiotus hufelandi and Mesobiotus harmsworthi groups (see e.g. Bertolani et al, 2014;Stec et al, 2018;Kaczmarek et al, 2018), sequences have not yet been obtained for many of the known species within these complexes, thus molecular data for the collected specimens belonging to these groups would not necessarily enable assignment to a known species or confirmation of new species status for the Diphascon pingue group sp. The resolution of the species identities of H. cf.…”

“…In his description Murray included an unnamed variety differing in the morphology of the egg. The eggs found among the Irish and Scottish beech litters exhibit internally sculpted areoles with reticulated processes and are of the "richtersi type" as defined by Kaczmarek et al (2018). However, the collected eggs exhibit variation in several features.…”

“…Mesobiotus harmsworthi (Murray, 1907) is the nominal species of a complex in which eggs are important for identifying taxa. Mesobiotus harmsworthi harmsworthi has been recently re-described by Kaczmarek et al (2018). Those authors clarified the description of the egg morphology for Mesobiotus harmsworthi, which had become confused throughout previous decades of varying reports.…”

“…For this reason, open nomenclature is used to designate the presence of at least one other Mesobiotus species in Scotland and Ireland that is not M. h. harmsworthi. This is not considered as a new taxon record for either country as the status of all records for the taxon made prior to the re-description are also reset to unidentified species of the harmsworthi group (Kaczmarek et al, 2018).…”