Antarcturus

Poore, Gary C. B., 2012, Marmachius, a spectacular new genus of Antarcturidae (Crustacea: Isopoda: Valvifera), Zootaxa 3559, pp. 61-68 : 62

Antarcturus zur Strassen, 1902

Type species. Antarcturus oryx zur Strassen, 1902 (subsequent designation by Stebbing 1908).

Antarcturus zur Strassen, 1902: 686.— Stebbing 1908: 52 –53.— Vanhöffen 1914: 519.— Tattersall 1921: 236 –237.— Nordenstam 1933: 122 –128.— Nierstrasz 1941: 258 –259.— Menzies 1962a: 194.— Menzies 1962b: 88.— Kussakin 1971: 241 –243.— Menzies & George 1972: 9.— Schultz 1978: 36.— Kussakin 1982: 273 –276.— Brandt 1990: 7 –10.— Wägele 1991: 144.

Diagnosis. Body weakly geniculate between pereonites 4 and 5, anterior pereon slightly elevated. Head with pair of submedian spines between eyes. Pereonites with supracoxal spines on all pereonites, with paired sublateral spines, without paired submedian spines (sometimes with tubercles), without middorsal spines. Pleonite 1 fused to remaining pleotelson; pleonites without middorsal spines, with paired submedian spines or tubercles, with pairs of sublateral tubercles or with few pairs of sublateral spines, none more prominent than others or with prominent pair of sublateral spines near midpoint, with marginal lateral spines, with prominent paired posterior sublateral spines, without prominent medial posterior spine dorsal to margin. Antenna 2 flagellum of 9 or more short articles. Pereopods 2–4 with regular rows of long setae along flexor margins of merus-propodus; unguis short, curved. Pleopod 1 of male exopod groove opening distolaterally on margin, scarcely produced at opening. Pleopod 2 of male, appendix masculina acute, about as long as endopod. Oostegites 2–4 supported by ventral coxal processes, largest on pereonite 4; oostegite 5 absent, without ventral coxal processes.

Remarks. Zur Strassen (1902) separated his new genus Antarcturus from Arcturus Latreille, 1829 on the basis of the absence of a lateral covering of the mouthparts; in Arcturus (and in Arcturidae s.s.) mouthparts and usually pereopod 1 are not visible in lateral view. His differentiation is now true of Antarcturidae and related families generally ( Poore 2001). Kussakin (1982) synonymised Dolichiscus Richardson, 1913 and ‘ Microarcturus ’ Nordenstam, 1933 with Antarcturus and his diagnosis was little more specific than that of zur Strassen. Dolichiscus is now regarded as a member of Austrarcturellidae ( Poore 2001) and ‘ Microarcturus ’ is a nomen nudum, albeit with several described species ( Poore 1991b). Zur Strassen (1902) included Arcturus coppingeri and Arcturus furcatus Studer, 1882 with his new species Antarcturus oryx but did not select a type species; Stebbing (1908) selected the last of these as type species. Kussakin (1982) incorrectly stated that the type species is Arcturus coppingeri Miers, 1881 .

In the context of diagnosing six new arcturid (now antarcturid) genera, Brandt (1990) rediagnosed and restricted Antarcturus on the basis of slender body shape, fused pleotelson segments, paired spines on the head and pereonites, two long posterior pleotelsonic spines, long antenna 2 with multiarticulate flagellum, subchelate pereopod 1, and pereopods 2–4 dactylus without long setae and with two ungues. Her characterisation of the cephalothorax (head plus pereonite 1) spination, “supraocular spines, followed by another pair of lobes, which bear one or more spines … followed by two smaller dorsomedial elevations; caudal margin of cephalothorax characterized by an elevation with several large or small spines ”, allows for some variability. Cephalothorax spination of members of this genus varies considerably; Brandt (1990) divided them into three groups, an oryx - group, hodgsoni -group and horridus -group on this basis. The pair of long posterior pleotelsonic spines seems universal in the 32 species presently assigned to Antarcturus . Half of the species described in the genus have been transferred to other antarcturid genera or to Dolichiscus Richardson, 1913 (Austrarcturellidae) , most by Brandt (1990). All except five of the species presently accepted are from Southern Ocean and Antarctica; four have been described from the north-western Pacific Ocean ( Kussakin 1982) and one from off the Galapagos Islands ( Benedict 1898).