| Summary: | Microthalestris santacruzensis sp. nov. urn:lsid:zoobank.org:act: 6A60E30B-3CF6-4E72-915D-0EF22C6BD66B Parastenhelia antarctica Scott, 1912 sensu Pallares (1963, 1968) Pallares (1963, 1968) recorded both sexes of a Parastenhelia species from the Río Deseado, Santa Cruz in Argentina. Although the material was attributed to P. gracilis it is radically divergent from both this species and P. antarctica in the shape of the female P5 exopod. In the Argentine specimens the inner margin and the proximal two-thirds of the outer margin are virtually straight while in both P. gracilis and P. antarctica they are distinctly convex. Additional differences can be observed in the length of some of its elements, in particular the proximal outer seta of the exopod which is clearly longer and the inner element on the endopodal lobe which is minute. Pallares (1968) states that the male P5 exopod has seven elements but does not figure the limb nor discloses the number of segments; however, in her Ph. D. dissertation (Pallares 1963) she stated “Exopodo con tres sedas externas, una interna y dos largas apicales” suggesting that all elements originate from a single segment and the total is six rather than seven. The Argentine material differs from all species currently assigned to Parastenhelia in the reduced armature formula of the swimming legs. Pallares (1968) only illustrates the male P3 and gives no information in the text about P2 and P4; however, the absence of inner setae on P2 exp-1 and - 2 in conjunction with the presence of only one inner seta on exp-3 differentiates the Río Deseado specimens from all known members of the genus. They further differ from P. gracilis in the length of the P1 exopod (exp-2 being distinctly longer) and the shape of caudal ramus seta V (swollen at the base). Although generally accepted as the first and only illustrated report of the male of P. gracilis (Mielke 1990; Bodin 1997; Wells 2007) there is no doubt that Pallares’s (1968) description deals with a different, as yet undescribed, species for ...
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