Rectarcturidae Poore, 2001

Poore, Gary C. B., 2013, Rectarcturidae Poore, 2001 rediagnosed with descriptions of new Australian genera and species (Isopoda: Valvifera), Memoirs of Museum Victoria 70, pp. 17-36 : 18-19

Rectarcturidae Poore, 2001

Rectarcturidae Poore, 2001: 227 . – Poore, 2003: 1843.

Diagnosis. Body strongly vaulted; head and pereonite 1 fused; pereonite 4 of similar length to pereonite 3; all pleonites fused into pleotelson. Body variously tuberculate or spinose but never with a posterior dorsolateral pair of strong spines on pleotelson; pleotelson without dorsolateral ridges ending in mediodorsal posterior spine. Dorsal coxal plates 2–7 obsolete, bases of pereopods exposed. Mouthparts and pereopod 1 visible in lateral view. Eyes well developed. Antenna flagellum of 2 articles plus distal claw. Pereopod 1 a gnathopod, pereopods 2–4 elongated, differentiated from ambulatory pereopods 5–7. Pereopod 1 dactylus evenly curved along anterior margin, evenly tapering. Pereopods 2–4 with long setae along flexor margins of ischium–propodus (up to 9 pairs per article, well-spaced), with short dactylus, unguis longer and setiform. Pereopod 4 similar to pereopod 3. Pereopods of males without dense fur of fine setae. Oostegites 1–4 functional, supported by coxal lobes, oostegites 5 present as articulating discs or absent. Penes fused as a single penial plate, apically simple. Pleopod 1 peduncle more elongate than on other pleopods, with marginal setae on rami longer than peduncle; exopod of male thickened laterally, with groove on posterior face ending distolaterally on an apex separated from a free distomesial lamina by a notch. Pleopod 2 of male with appendix masculina as long as or longer than endopod, basally less than half width of endopod. Uropodal exopod tapering, with 2–3 stout distal setae.

Remarks. The family was erected for one genus, Rectarcturus Schultz, 1981 , on the basis of a cladistic analysis of the Valvifera ( Poore, 2001). The diagnosis given above differs from the original in some important features. Pereopods 2–4 are described as possessing up to nine pairs of well-spaced long setae per article along the flexor margins of the merus– propodus. These setae are more spaced and fewer than those on Arcturidae and Antarcturidae . It is now realised that oostegites 1–4 are supported by coxal lobes, and that a vestigial oostegite 5 is present as a lobe in three of the four genera. The structure of the male pleopod 1 exopod is better defined as above.

Species of the family are recognisable, and distinguished from arcturids, antarcturids and austrarcturellids, by their straight bodies and reduced setation of pereopods 2–4. The structure of the male pleopod 1 exopod separates rectarcturids from other ‘straight’ families—the groove ends in a distolateral lobe separated from a distomesial lamina by a deep notch (see Poore, 2001: fig. 3 for examples from other families). Monotypic Xenarcturidae is also straight but has a flat body and ambulatory pereopod 4. The only species of Arcturididae is straight and cylindrical, and all pereopods except the first are essentially ambulatory. Pseudidoteidae have almost raptorial pereopods 2–4 ( Poore and Bardsley, 2004), and Holidoteidae have a uniquely structured male pleopod 1 exopod and uropodal rami ( Poore, 2003). Schultz (1981) diagnosed his new genus as a member of Arcturidae , but none of the characters he chose is especially diagnostic except for ‘body much straighter than in most arcturids’. Schultz (1981) included four species. One of these, Microarcturus laevis is now Austroacturus laevis ( Kensley, 1975) , a member of Holidoteidae . Park and Wägele (1995) noted that another, Arcturus patagonicus Ohlin, 1901 , is clearly geniculate between pereonites 4 and 5, and has a pair of sharp submedian spines on the head. They placed it in Neoarcturus , which they thought of as similar to Rectarcturus ; Neoarcturus and some of the species they listed are also in Holidoteidae , but not this one. It and others from their list are now placed in the antarcturid genus Fissarcturus Brandt, 1990 ( Poore, 2003). Another, Rectarcturus tatianae Kussakin and Vasina, 1995 , from 6000 m depth in the South Atlantic, is a geniculate species, so is not in this genus as presently defined. Its setiform unguis on pereopods 2–4, short antennal flagellum, male pleopod 2 structure, and paired body tuberculation suggest another species of Fissarcturus , but without the prominent posterior pleotelsonic spines.

The two species of Rectarcturus are from Argentina. Australian species that can be placed in the family are sufficiently different from Rectarcturus and diverse to warrant three new genera. They are diagnosed and four new species described here. The poorly described Arcturus simplicissimus Whitelegge, 1904 is allocated to one of the new genera on the basis of the description of a neotype.

The four genera are separated on the basis of differences in overall sculptural patterns, the male pleopod 1 exopod, setation, shape and proportion of the antenna and pereopods 2 and 3. The key uses the most conveniently observed characters; a key based on the structure of the male pleopod 1 exopod would lead to different dichotomies. Whereas in Rectarcturus and Tasmarcturus gen. nov. the groove on the posterior face of the male pleopod 1 exopod ends obliquely on a truncate distolateral lobe, not extending beyond the distomesial seta-bearing lamina, in Nowrarcturus gen. nov. it ends on a conical apical projection, extending beyond the lamina. The male of Galathearcturus gen. nov. is unknown, but its only species differs sculpturally from all others.

Key to genera and species of Rectarcturidae

1. Antenna less than twice dorsal length of (head + pereonite 1); article 4 subspherical, about as long as fused articles (1 + 2); article 5 at least twice as long as article 4; pereopod 2 (dactylus body + unguis) 3 times as long as propodus 2

– Antenna at least 2.5 times dorsal length of (head + pereonite 1); article 4 cylindrical, at least twice as long as fused articles (1 + 2); article 5 shorter than or at most 1.5 times as long as article 4; pereopod 2 (dactylus body + unguis) shorter or at most 2.5 times as long as propodus 5

2. Head with paired, submedian tubercles, pereonites with smooth, transverse ridges, anterior pleonites barely elevated; antenna article 3 cuboid, as long as deep, without ventrolateral flange (fig. 2) Galathearcturus antoniae

– Head, pereonites and anterior pereonites with paired blade-like submedian and sublateral tubercles/carinae, all secondarily tuberculate; antenna article 3 cuboid, as long as or little longer than deep, with ventrolateral teeth (fig. 1b–d) Tasmarcturus 3

3. Head ornamentation of strong acute tubercles separated in lateral view; submedian processes on pereonite 3 erect, digitiform, spinulose, especially in female, with prominent secondary process posteriorly (fig. 1d) Tasmarcturus simplicissimus

– Head ornamentation of flat tubercles almost contiguous in lateral view; submedian processes on pereonite 3 longitudinally flattened 4

4. Head ornamentation rounded anteriorly in lateral view (fig. 1c) Tasmarcturus lewisi

– Head ornamentation prominently square anteriorly in lateral view (fig. 1b) Tasmarcturus erinae

5. Head with paired submedian tubercles, pereonites with smooth transverse ridges (pereonite 3 with second ridge anterior to major one), anterior pleonites barely elevated (fig. 1a) Nowrarcturus jamesi

– Head, pereonites and anterior pleonites with paired blade-like submedian and sublateral tubercles or carinae, smooth or barely secondarily ornamented Rectarcturus 6

6. Sculpture dominated by rows of submedian, sublateral, lateral and supracoxal longitudinal blades Rectarcturus kophameli

– Sculpture dominated by rows of submedian, sublateral, lateral and supracoxal longitudinal complex tubercles Rectarcturus tuberculatus