Microthalestris variabilis, sp. nov.

• Main Authors: Huys, Rony, Mu, Fanghong
• Format: Other/Unknown Material
• Language: unknown
• Published: 2021
• Subjects: Biodiversity; Taxonomy; Animalia; Arthropoda; Hexanauplia; Harpacticoida; Miraciidae; Microthalestris; Microthalestris variabilis; King George Island; Argentine; Seta; Ushuaia; Maxwell Bay; isla Grande; Tierra del Fuego
• Online Access: https://zenodo.org/record/5579339; https://doi.org/10.5281/zenodo.5579339

Microthalestris variabilis sp. nov. urn:lsid:zoobank.org:act: 5CD772EB-A539-4FF2-B83E-531ED6767E80 Parastenhelia? costata Pallares, 1982 sensu Mielke (1990) Based solely on P1 morphology P. gracilis appears morphologically close (and potentially conspecific) with P. costata, another Argentine species originally described from Bahía Thetis on the east coast of Tierra de Fuego (Pallares 1982: 9–11; Plates I–II) and which occurs sympatrically with M. minuta comb. nov. (Pallares 1982: 12–14; Plate III). Bick & Arlt (2013) recorded both species in considerable numbers from a soft-bottom area in Maxwell Bay (King George Island, South Shetlands) but it is not clear how they distinguished them. Mielke (1990) reported a second population on Isla Grande Tierra del Fuego from Bahía Lapataia near Ushuaia which he tentatively attributed to P. costata. An exceptionally high degree of variability in the armature of P2–P4 was observed in a relatively small sample (13 ♀♀, 6 ♂♂), causing Mielke (1990) to suggest that both Tierra del Fuego species, P. costata and P. minuta represented populations of the same species. Accepting this view would unnecessarily blur the species boundaries in Microthaletris even further and, considering the recent progress that has been made (e.g. Gee 2006), be a retrograde step in the revision of the genus. Mielke’s (1990) specimens differ from the P. costata type population in the smaller body size [580–780 μm (♀), 420–560 μm (♂) vs 789–960 μm (♀), 600–706 μm (♂)], the shape of caudal ramus seta IV (with bulbous swelling near the base), the presence of only one or two inner setae (instead of three) on P3–P4 exp-3, the length of the inner seta on the male P3 enp-2, and the weakly developed endopodal lobe of the male P5, reaching barely beyond the proximal exopod segment (vs reaching well beyond the middle exopod segment). The female P5 differs in the shape of the exopod which is rounder in the type population and shows a wider spacing between the proximal and middle outer setae, and in the length ...