Resolving the systematics of Richtersiidae by multilocus phylogeny and an integrative redescription of the nominal species for the genus Crenubiotus (Tardigrada)

Abstract

The family Richtersiidae, although established recently with the use of phylogenetic methods, was considered potentially paraphyletic at the time of its erection. Until now, the family comprised four genera, Richtersius, Diaforobiotus, Adorybiotus and a newly erected genus Crenubiotus. However, the genetic characterisation for the latter two genera was very limited or absent. To address concerns about the phylogenetic affinity of these two genera, we present a multilocus phylogeny of the families Richtersiidae and Murrayidae based on four molecular markers (18S rRNA, 28S rRNA, ITS-2 and COI). Our results show a distinct evolutionary lineage composed of Adorybiotus and Crenubiotus, which is sister to Murrayidae. In order to accommodate the phylogenetic and morphological distinctiveness of this lineage, we erect a new family, Adorybiotidae fam. nov. The new taxon differs morphologically from other families in the superfamily Macrobiotoidea by a unique combination of traits: (1) the presence of tubercles/cushions with aggregations of microgranules on their surfaces present on all legs and on the dorso-caudal cuticle, (2) a system of internal septa in claws, and (3) buccal apparatus morphology. Moreover, in order to stabilise the taxonomy and nomenclature in the genus Crenubiotus, we redescribe its type species, Crenubiotus crenulatus, by means of integrative taxonomy and designate a new neotype based on a population from the original terra typica.

An integrative description of a new Richtersius species from Greece (Tardigrada: Eutardigrada: Richtersiusidae)

“…1.8 template available from the Tardigrada Register (Michalczyk & Kaczmarek 2013) and are provided as Supplementary Material (SM.01 and SM.02). Tardigrade taxonomy follows Bertolani et al (2014), Stec et al (2020b) and Guidetti et al (2021).…”

“…Specifically, the new genus Crenubiotus Lisi, Londoño et Quiroga, 2020 was erected using classical taxonomic methods and detailed morphological examination of the animals and eggs of Macrobiotus crenulatus (Richters, 1904) as well as those of a very similar new species from Colombia, and then placing the new genus within the family Richtersiidae. Subsequently, Stec et al (2020b) integratively redescribed Crenubiotus crenulatus, pinpointing its phylogenetic position within Macrobiotoidea. The analysis, in addition to the new genetic data for two analysed Crenubiotus species, also included novel genetic data for Adorybiotus cf.…”

“…granulatus, demonstrating the presence of a distinct evolutionary lineage composed of Adorybiotus and Crenubiotus. In order to acknowledge the phylogenetic and morphological distinctiveness of this lineage, (Stec et al 2020b) erected a new family, Adorybiotidae Stec, Vecchi et Michalczyk, 2020. Soon after, Guidetti et al (2021 described an additional new Crenubiotus species from Germany, presenting its phylogenetic position that was congruent with the results provided by Stec et al (2020b).…”

“…In order to acknowledge the phylogenetic and morphological distinctiveness of this lineage, (Stec et al 2020b) erected a new family, Adorybiotidae Stec, Vecchi et Michalczyk, 2020. Soon after, Guidetti et al (2021 described an additional new Crenubiotus species from Germany, presenting its phylogenetic position that was congruent with the results provided by Stec et al (2020b). Moreover, Guidetti et al (2021) changed the name of the family Richtersiidae into Richtersiusidae Guidetti, Schill, Giovannini, Massa, Goldoni, Ebel, Förschler, Rebecchi et Cesati, 2021, because the former was a junior homonym of a nematode family.…”

Reaching the Monophyly: Re-Evaluation of the Enigmatic Species Tenuibiotus hyperonyx (Maucci, 1983) and the Genus Tenuibiotus (Eutardigrada)

“…Over the last ten years, the implementation of molecular techniques and taxonomic analyses by means of an integrative approach have accelerated the emergence of new species being characterized morphologically and genetically in detail, e.g., [5][6][7][8][9][10][11][12]. The acquisition and accumulation of genetic data tightly associated with phenotypic information enhanced studies on two major subjects in tardigrade taxonomy: (i) The recognition and disentanglement of cryptic/pseudocryptic diversity, e.g., [13][14][15][16][17][18][19] and (ii) the construction of comprehensive molecular phylogenies at the family level or higher that considerably impacted tardigrade systematics, e.g., [20][21][22][23][24][25][26][27][28][29][30]. Notably, there were not only integrative descriptions of new species for science that have contributed greatly to these subjects' investigation, but also revisional notes with updated diagnoses and new information on already-known taxa, e.g., [31][32][33][34][35][36][37].…”