Thermoarcturidae

Poore, Gary C. B., 2015, Thermoarcturidae, a new crustacean family of three genera (Isopoda: Valvifera), Zootaxa 4007 (3), pp. 409-418 : 410-411

Thermoarcturidae n. fam.

Type genus. Thermoarcturus Paul & Menzies, 1971 .

Diagnosis. Body flexed between pereonites 4 and 5. Head and pereonite 1 fused. Pereonite 4 of similar length to pereonite 3. All pleonites fused into pleotelson, suture visible in at least 1 species. Body tuberculate or spinose, with at least dorsolateral pairs of spines, not dominated by pair near end of pleotelson; cuticle finely tomentose; 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 small or absent. All limbs covered in fur of fine setae. Antennal flagellum of 2 articles plus distal claw. Maxillipedal palp compact, article 3 as wide as long or wider than long, with mesiodistal notch. Pereopod 1 gnathopod-like, pereopods 2–4 differentiated from ambulatory pereopods 5–7. Pereopod 1 dactylus evenly curved along anterior margin, evenly tapering, with mesial stiff seta(e). Pereopods 2–4 with marginal and mesial rows of well-spaced long stiff setae; with prominent dactylus, unguis at least half as long as dactylus; pereopod 4 similar to pereopod 3. Pereopods of males without dense fur of fine setae along flexor margins. Uropodal endopod and exopod triangular, of similar lengths, each with terminal robust seta(e). Oostegites 1–4 functional, supported by coxal lobes; oostegites 5 a pair of rounded plates. Penes fused as a single penial plate, apically barely slit. Pleopod 1 peduncle more elongate than on other pleopods; with marginal setae on rami longer than or equal to length of rami. Pleopod 1 exopod of male thickened and with groove on posterior face, ending laterally on complexly lobed margin, or without groove and setose. Pleopod 2 of male with appendix masculina as long as or longer than endopod, basally less than half width of endopod.

Remarks. The diagnosis is based on that of Antarcturidae ( Poore 2001) which the new family most resembles. The most significant feature uniting members of the family is the arrangement of setae on pereopods 2–4, widely spaced, more or less alternating lateral and mesial, and stiff, without associated groups of shorter finer setae. All members of Antarcturidae have pairs of long flexible ‘filter-setae’ and associated shorter finer setae ( Fig. 1). These extend in Chaetarcturus Brandt, 1990 and Caecarcturus Schultz, 1981 on to the dactylus. In Thermoarcturidae the dactylus has one or more stiff mesial setae. In all species of Thermoarcturidae the uropodal rami are triangular and of similar lengths, the exopod only a little smaller, and have terminal robust setae. In Antarcturidae the exopod is rectangular with distal setae and shorter than the endopod. Oostegites 5 are present in the two genera for which females are known; the female is unknown in Califarcturus tannerensis ( Schultz, 1966) comb. nov. whereas they are absent in all antarcturids. The maxillipedal palp is compact, article 3 wider than long with a mesiodistal notch in Spinarcturus and Califarcturus , or as wide as long in Spinarcturus ; the palp is more linear in most antarcturids but similar to Spinarcturus in some genera. Lastly, the cuticle of the body and all limbs (antennae, maxillipeds, pereopods) are covered in a fur of fine setae not seen in Antarcturidae .

The family Rectarcturidae Poore, 2001 (of seven southern species) and Arcturididae Poore, 2001 (of one species) were differentiated from Antarcturidae on body shape, structure of the male pleopod 1 and setation of the pereopods and reviewed in detail by Poore (2013). Rectarcturids have similar setation of pereopods 2–4 to that of thermoarcturids and also usually have small paired oostegites 5. However, all rectarcturids have straight nongeniculate bodies, long narrow dactyli and setiform ungues on pereopods 2–4. In Rectarcturidae the aperture of the groove on the exopod of pleopod 1 of the male is subdistal or distal on a lobe separate from the laminar exopod apex. The situation is somewhat similar in Califarcturus tannerensis and Thermoarcturus venezuelensis , but the latter is uniquely different from all rectarcturids and antarcturids with ancillary pleopodal structures without apparent homologies in other genera. Spinarcturus natalensis Kensley, 1978 differs from both, having a weak exopodal groove and a tuft of fine setae similar to that seen in the more distantly related arcturid genus Arcturus Latreille, 1829 ( Poore 2001) . Arcturides cornutus Studer, 1882 the only species of Arcturididae , has a straight body and only robust setae on pereopods 2–4.

The strong stiff setae on pereopods 2–4 bear a superficial similarity to those seen in species of the arcturid genus Parastacilla Hale, 1924 ( King 2000) but otherwise the taxa differ in the many family-level characters, notably the concealed mouthparts, elongate pereonite 4 and male pleopods.