Two New Species of the Mite Genus Stereotydeus Berlese, 1901 (Prostigmata: Penthalodidae) from Victoria Land, and a Key for Identification of Antarctic and Sub-Antarctic Species

Abstract

Two new mite species belonging to the genus Stereotydeus Berlese, 1901 were discovered from locations along the coast of Victoria Land, continental Antarctica. Previous records of this genus in the area under study only reported the presence of S. belli and S. mollis. Although those studies included no morphological analyses, it has since been assumed that only these species were present within the area. Specimens of S. ineffabilis sp. nov. and S. nunatakis sp. nov. were obtained, sometimes in sympatry, from four different localities in Central and South Victoria Land and are here described and illustrated using optical and scanning electron microscopy (SEM) techniques. Features useful for identification of the two new Stereotydeus species include the size of the specimens, the length of the apical segment of pedipalps, the presence/absence of division of the femora, the position of solenidia, the shape and disposition of the rhagidiform organs on the tarsi, the shape of the apical setae of the tarsi, the numbers of aggenital setae and the position of the anal opening. A key to 14 of the 15 currently described Antarctic and sub-Antarctic Stereotydeus species is provided.

Overlooked Species Diversity and Distribution in the Antarctic Mite Genus Stereotydeus

“…In parallel to this study, morphological analyses have been performed on numerous specimens (between 20-50 for each sampled species, data not published). The morphological comparisons clearly defined the boundaries between all the Stereotydeus species occurring on Victoria Land, as recently published in Brunetti et al [48], where not only the new species of S. ineffabilis and S. nunatakis are described, but also all the characters so far used to describe and distinguish the Antarctic Stereotydeus species are reviewed (see [48] Tables A1-A7), and the keys to identification are provided. Unfortunately, the lack of specimens of S. mollis, S. shoupi and S. villosus from accessible localities prevented us from improving the original descriptions with the new characters studied in these species and, therefore, were not available for combined morphological analyses.…”

“…9.49 9.9 9.9 10.1 10.1 9.9 9.7 9.9 9.9 9.7 9.9 9.7 9.9 10.1 9.9 10.1 8.89 6.46 6.26 6.26 6.46 0 MB9 9.29 9.7 9.7 9.9 9.9 9.7 9.49 9.7 9.7 9.49 9.7 9.49 9.7 9.9 9.7 9.9 9.09 6.67 6.46 6.46 6.67 0.2 0 MB8 9.49 9.9 9.9 10.1 10.1 9.9 9.7 9.9 9.9 9.7 9.9 9.7 9.9 10.1 9.9 10.1 8. 48 12.9 12.1 11.5 11.9 11.9 12.12 12.3 12.5 13.1 13.94 13.5 12.9 13.5 13.3 13.5 12.9 12.9 15.8 14.1 0 Stereotydeus sp.a 12.3 12.7 12.7 12.9 12.9 13.7 13.3 13.3 13.7 13.5 13.3 13.9 13.1 13.3 13.1 13.1 12.1 9.49 9.7 9.7 9.7 11.11 11.1 10.7 10.9 12.32 11.9 11.7 11.7 11.5 11.9 13.7 13.7 13.3 15.4 14.1 0 Stereotydeus sp.b 12.3 12.7 12.7 12.9 12.9 13.7 13.3 13.3 13.7 13.5 13.3 13.9 13.1 13.3 13.1 13.1 12.5 9.49 9.7 9.7 9.7 11.52 11.5 11.1 10.9 12.73 11.9 11.7 11.7 11.5 11.9 13.7 13.7 13.9 15.6 13.9 1.21 0 S. villosus 12.9 12.9 12.9 13.1 13.1 13.1 12.7 13.1 12.9 12.7 12.9 13.1 12.9 13.1 12.7 13.1 13.9 10. 5 Green frame-S. ineffabilis; orange frame-S. delicatus; red frame-S. punctatus; purple frame-S. belli; blue frame-S. nunatakis; light blue frame-S. ineffabilis.…”

“…Due to the small size of the specimens and, consequently, of the characteristics useful for an accurate taxonomic determination, 22 adult individuals (13 S. ineffabilis from four localities and 9 S. delicatus from Campo Icaro; Table 2) were selected for the joint morphological/molecular investigation and also used in all the molecular analyses. Only adult specimens were considered in the morphological comparison because, at the nymphal stages, most of the characteristics useful for the positive identification of Stereotydeus species are not yet developed (e.g., small size, sex structures not developed, division of the femora absent or incomplete, reduced number of aggenital and genital setae, and reduced number of rhagidial organs; see [48]).…”

“…Indeed, after early morphological studies in the 1960s [43][44][45], few studies on the physiology and ecology of the genus have been conducted [11][12][13]40,46,47], these are particularly focusing on S. mollis. Very recently, two new Stereotydeus species (S. ineffabilis and S. nunatakis) have been described from an area of Victoria Land [48], bringing the number of known Antarctic and sub-Antarctic members of the genus to 15 [48]. Focusing on Victoria Land, five species (S. delicatus Strandtmann, 1967, S. punctatus Strandtmann, 1967, S. belli Trouessart, 1902, S. ineffabilis Brunetti and Siepel, 2021 and S. nunatakis Brunetti, 2021) are currently known from North Victoria Land and two (S. mollis and S. shoupi Strandtmann, 1967) from South Victoria Land and the central Transantarctic Mountains [36].…”

“…At the same time, given the recent discovery of the two new Stereotydeus species in Northern Victoria Land in a study that also reviewed the morphological characters relevant to the identification of Antarctic Stereotydeus species [48], the question of a possible overlap between these new taxa with the species already known from the area (S. belli, S. punctatus and S. delicatus) and with S. mollis from Southern Victoria Land has to be addressed. In addition to that, the current lack of genetic knowledge of a species morphologically described more than fifty years ago needs addressing, not only for the systematic understanding of the genus, but also to contribute to the future development and implementation of sustainable conservation planning in Antarctica.…”