Neoarcturus kensleyi, Poore, 2003

Poore, G. C. B., 2003, Revision of Holidoteidae, an endemic southern African family of Crustacea, and re-appraisal of taxa previously included in its three genera (Isopoda: Valvifera), Journal of Natural History 37, pp. 1805-1846 : 1822-1827

Neoarcturus kensleyi n. sp.

(figures 6F, 8–10)

Microarcturus oudops: Kensley, 1978b : figure 13a; Kensley, 1984: 252 (part), figure 19a.

Material examined

South Africa, KwaZulu-Natal to Transkei , 680 m (stn SM 103 ): holotype male 5.2 mm, SAM A43165 ; paratype male 5.2 mm, paratype female 5.1 mm, three juveniles 4.4–4.8 mm, SAM A17819 .

South Africa, Cape Point area , 1400 m: two paratype ovigerous females 4.8 mm, SAM A41950 .

Diagnosis

Eyes colourless. Dorsum irregularly tuberculate, especially on transverse ridges, without dominant spines. Pereonites 2–4 with weak triangular lateral wings in female (obsolete in male); pereonites 5–7 and pleonites obsoletely produced. Pleotelson apex broadly acute, not apically produced as spine, posterolateral margins evenly convex. Male pleonite 2 strongly elevated as paired dorsolateral bosses, pleonite 3 with lower dorsomedial boss. Posteroventral margin of pereonite 4 of male deeply incised, with pair of tubercles on margin. Male to 5.2 mm; female to 5.1 mm.

Description

Colour. Clear white.

Body of paratype female. Head with ocular lobes lateral; eyes colourless, separated by notch from lateral margin of maxillipedal somite. Pereonites 1–3 with broad rounded transverse ridges, more pronounced dorsolaterally. Pereonite 4 with dorsal transverse ridge bounded laterally by longitudinal ridge running anteriorly from it. Pereonites 2–4 with second obsolete transverse ridge anterior to major one. Pereonites 5–7 and pleonites 1 and 2 with dorsal transverse ridges. Pleonite 3 with lower medial dorsal boss. Remaining pleotelson evenly domed dorsally and with evenly curved to broadly acute apex. Coxa of pereopod 1 triangular; lateral tergal extensions of pereonites 2 and 3 rounded and barely extended beyond coxae, peronite 4 less so. Coxae 5–7 rounded in dorsal view. Whole dorsal and lateral integument (and peduncles of antenna 2, bases of pereopods 5–7, uropod and oostegite coxal supports) irregularly tuberculate-thorny, without enlarged tubercles.

Body of holotype male. Pereonites 1–7 and pleonite 1 with more acute transverse ridges than in female. Pereonites 1–3 with small lateral dimple on each ridge. Lateral margin of pereonite 4 defined by longitudinal ridge. Pleonite 2 with ridge especially elevated and dorsolaterally expanded. Pereonites 2–4 with second transverse ridge anterior to major one more pronounced than in female. All pereonites with obsolete lateral projections. Integument more spinulose than in female, extending on to bases–ischia of pereopods 5–7, and to sternites of pereonites. Posterior ventral margin of pereonite 4 deeply incised, bearing pair of submedial spinulose tubercles; anterior margin of pereonite 5 with spinulose medial projection.

Limbs of male. Antenna 2 peduncle 54% of total body length; ratio of articles 3–5 and flagellum, 10:18:18:10; ratio of flagellum articles 100:74:40; antenna 2 with more or less regular clusters of setae along lower margin.

Mandible and maxillae not dissected.

Maxillipedal endite evenly curved distolaterally, sparsely setose. Maxillipedal palp articles 1–5 with ratio of lengths 28:43:100:71:24; articles 1–5 with 0, 4, 10, 10, 5 medial and posterior facial setae, respectively, most serrulate; article 3 the widest, article 4 68% of greatest width of article 3, article 5 42% width of article 4.

Pereopod 1 merus anterodistally tuberculate; carpus posterodistally tuberculate; propodus oval, width 43% length; dactylus (including unguis) 75% propodus; ischium and merus with long simple setae along and near posterior margin; carpus with six posterior serrulate setae; propodus with ten posterior serrulate setae, 34 mesial facial simple and serrulate setae loosely arranged in oblique rows; dactylus with oblique row of eight serrulate setae and one more proximal on anterior margin; unguis 55% length of body of dactylus, minutely serrate; secondary unguis half unguis length, minutely serrate.

Pereopod 2 with propodus as long as carpus; secondary unguis absent; basis–propodus with setae along posterior margin, in five to six pairs of long setae accompanied by shorter one on carpus–propodus. Pereopod 3 similar to pereopod 2, propodus 80% length of carpus; body of dactylus 42% length of propodus; unguis 1.9 times as long as dactylus body (ratios differ slightly). Pereopod 4 with propodus 75% length of carpus; body of dactylus 45% length of propodus; unguis 90% length of dactylus body; secondary unguis present, third length of unguis. Pereopods 5–7 progressively shorter, carpus and propodus each with three and four posterior robust setae, respectively.

Pleopod 1 exopod 64% length of endopod; endopod with three plumose setae on distomesial margin; this margin exceeded by rounded setulose lobe; groove on posterior face opens on lateral margin at base of this lobe; lateral margin defined distally by notch proximal to groove opening, with 13 submarginal simple setae along posterior face, becoming closer together distally, and with four thick setulose setae on anterior face distally. Pleopod 2 exopod with 12 lateral and ten distal plumose setae; endopod slightly exceeding exopod, with one medial and 12 distal setae; appendix masculina longer than endopod by 10% of its length, with a mesial longitudinal field of rows of fine setae, apex with mesial swelling and oblique angle laterally.

Uropod exopod less than half length of endopod, both rami with distal seta, that on exopod well exceeding endopod.

Etymology

The species is named for Brian Kensley whose contributions to knowledge of the southern African isopod fauna make the region exceptionally well documented.

Remarks

The species was confused with N. oudops by Kensley (1978b) who figured the two species under the latter name on the one page and reproduced the figure of N. kensleyi as N. oudops in his 1984 guide-book (Poore, 1991). The new species is most easily distinguished from N. oudops in lacking angles on the posterolateral margins of the pleotelson. The transverse ridges which dominate each pereonite are evenly and finely tuberculate whereas in N. oudops they bear pairs of larger tubercles among the smaller ones. All preserved specimens are clear white while those of N. oudops are muddy yellow. Both have colourless eyes.

Neoarcturus kensleyi co-occurs with N. oudops and is known from only two localities off KwaZulu-Natal to Transkei , eastern South Africa, and the Cape area, south-western South Africa, at 680 and 1400 m depth .