Oxyarcturus Brandt, 1990

Pereira, Emanuel, Roccatagliata, Daniel & Doti, Brenda L., 2023, Revision of the genus Oxyarcturus (Isopoda, Valvifera, Antarcturidae), with a description of a new deep-sea species from Argentina, Zoosystematics and Evolution 99 (2), pp. 457-472 : 457

Genus Oxyarcturus Brandt, 1990

Oxyarcturus Brandt, 1990: 73-74;- Wägele 1991: 138;- Poore 2001: 224.

Type species.

Arcturus spinosus Beddard, 1886.

Diagnosis

(modified from Brandt 1990). Body slender and geniculate; dorsal surface covered with many spines. Head with two long supraocular spines, followed by two (or more) long posterior supraocular spines. Eyes well developed, lateral, rounded or rather oval. All pleonites fused with pleotelson, pleonites 1-3 separated by transverse grooves. Pleotelson with two long caudolateral spines, and a single subterminal medial spine in between. Antenna longer than body, flagellum multiarticulate with at least 8 articles. Pereopod I developed into a strong subchela, dactylus not swollen. Pereopods II-IV, dactylus without filter setae.

Remarks.

Brandt (1990) in a comprehensive work of the Antarctic Valvifera revised the old genus Antarcturus zur Strassen, 1902, and transferred 17 of the species previously placed in this genus to Acantharcturus Schultz, 1981, Chaetarcturus Brandt, 1990, Litarcturus Brandt, 1990, Tuberarcturus Brandt, 1990 and Oxyarcturus Brandt, 1990. Brandt (1990) erected the genus Oxyarcturus to include three species: O. spinosus (Beddard, 1886), O. dubius (Kussakin, 1967) and O. beliaevi (Kussakin, 1967); and stated that members of this genus have "caudal margin of pleotelson with 3 acute spines, two long laterocaudal ones and one shorter medial spine"; being this the only feature characterizing the genus. Although this medial spine is evident in O. spinosus (type species) and O. holoacanthus sp. nov. (see Beddard (1886); current study Figs 1A, B , 2C ), the presence of this spine in O. dubius and O. beliaevi is uncertain. Unfortunately, Kussakin (1967) did not include figures in dorsal view of O. dubius and O. beliaevi . However, he wrote that O. dubius has "very small, weakly expressed spinules, largest of which were disposed in midline near posterior margin of pleotelson". Regarding O. beliaevi , although Kussakin (1967) did not mention the presence of a medial spine in this species, Kensley (1977, 1978) reported this spine in specimens from South Africa. However, Wägele (1991) and Kussakin and Vasina (1995) questioned Kensley’s identification.

In addition, Kussakin (1967) stated that O. dubius has numerous long setae on the internal margin of the five distal articles (ischium to dactylus) on the pereopods II-IV. Within Antarcturidae , the presence of filter setae on the dactyli of the pereopods II-IV is characteristic of the species of the genera Chaetarcturus Brandt, 1990, Mixarcturus Brandt, 1990, Caecarturus Schultz, 1981 and Glaberarcturus Kussakin & Vasina, 1998 ( Schultz 1981; Brandt 1990; Kussakin and Vasina 1998).

O. dubius (Kussakin, 1967) is clearly not a member of Oxyarcturus , and O. beliaevi (Kussakin, 1967) probably neither. Therefore, these two species are herein removed from the genus Oxyarcturus and placed as incertae sedis, until further morphological and molecular data can clarify their taxonomic position.

On the other hand, the specimens from South Africa identified by Kensley (1977) as Antarcturus beliaevi most probably belong to a new species of Oxyarcturus . If confirmed to be a new species, its description should be completed, one specimen should be designated as holotype, and a formal name should be adopted.

Species included.

O. spinosus (Beddard, 1886); O. holoacanthus sp. nov., and probably Antarcturus beliaevi Kussakin, 1967 sensu Kensley 1977.

Figures

Figure 1. Oxyarcturus holoacanthus sp. nov. Photographs. Holotype male (MACN-In 44318). A. Habitus, lateral view. Paratype male (MACN-In 44319 - a); B. Pleon, dorsal view. Paratype female (MACN-In 44319 - b); C. Head and pereonites 1 - 4, dorsal view; D. Habitus, lateral view. cl - caudolateral spine; m - medial spine; l - lateral spine.

Figure 2. Oxyarcturus holoacanthus sp. nov. Holotype male (MACN-In 44318). A. Habitus, lateral view; B. Head and pereonite 1 dorsal view (arrowhead point pereonite 1 spines). Paratype male (MACN-In 44319 - a); C. Tip of pleotelson, dorsal view. sm - submedial spine; sl - sublateral spine; l - lateral spine.