Microthalestris santacruzensis, Huys, Rony & Mu, Fanghong, 2021

Huys, Rony & Mu, Fanghong, 2021, Johnwellsia, a new intertidal genus of Parastenheliidae (Copepoda, Harpacticoida) from the Taiwan Strait, China, including a review of the family and key to genera, Zootaxa 5051 (1), pp. 236-318 : 280-281

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 which we coin the name P. santacruzensis sp. nov. Pallares (1975), in a subsequent report on littoral harpacticoids from Tierra de Fuego, recorded P. gracilis from Bahía Cook on Isla de Los Estados (Tierra del Fuego) but the authenticity of this record remains to be confirmed.

Original description. Pallares (1968): 63–65, Plate XIX.

Type material. Pallares’s (1968) original material no longer exists (M. Sciberras, pers. commn). The dissected male specimen illustrated by Pallares (1968: 64) in her Plate XIX is here designated as the holotype of P. santacruzensis sp. nov. ( ICZN Arts 16.4 and 72.5.6). The species can be differentiated by the characters listed in the diagnosis below and those mentioned and illustrated in Pallares (1968) ( ICZN Art. 13.1).

Type locality. Pallares (1968) collected material from a number of localities in the Deseado River, Santa Cruz Province, Argentina: Punta Cavendish, Dos Hermanas, Punta Guanaco, Restinga Chaffers, Isla Quiroga and Bahía Uruguay. Since Pallares (1968) did not specify which specimens she based her illustrations on, the type locality encompasses all of their respective places of origin ( ICZN Art. 73.2.3).

Differential diagnosis. Microthalestris . Body length 890 μm in ♀, 700 μm in ♂. Antennule 9-segmented and haplocer in ♂. Antenna with 2-segmented exopod bearing two setae on exp-1 and one lateral and three apical elements on exp-2; endopod without penicillate spines. P1 exopod about 0.8 times length of endopod; exp-2 elongate, about 2.5 times as long as exp-1. P3 exopod armature pattern [0.0.123]; endopod ♂ 3-segmented, with apophysis on enp-3, armature pattern [1.1.02 + apo]. P 5 ♀ with elongate exopod (about 3.2 times as long as wide), inner margin and proximal two-thirds of outer margin straight, with six elements, proximal outer one long, outer apical one minute; endopodal lobe with five elements, innermost one minute. P 5 ♂ with six elements on 1-segmented exopod; endopodal lobe with two elements. P 6 ♂ with three setae. Anal operculum smooth. Caudal ramus seta V with swollen base .

Etymology. The species is named after the Santa Cruz Province, located in the southern part of Argentina where the type locality is located.