Acutiserolis spinosa

Acutiserolis spinosa (Kussakin, 1967)

Figs 1 a-f; 2–4

Serolis spinosa Kussakin 1967 (1968): 247–249, figs 15, 16.

Acutiserolis spinosa.– Brandt 1988: 21.

Serolis (Acutiserolis) spinosa.– Wägele 1994: 53.

Material examined. Ross Sea, Antarctica (65.4755°S, 161.0480°E– 65.4828°S, 161.0458°E), 760– 750 m, 7 Mar 2004, (NIWA stn TAN0402/269), NIWA 23526 (figured male, 34 mm; ovigerous female, 30 mm; 2 juvenile males, 25 and 29 mm;

juvenile female, 28 mm), NIWA 24311 (ovigerous female, 31 mm), NMV J58091 (ovigerous female, 32 mm).

Type material. Region of Scott Island, East Antarctica, 500–900 m (Ob stn 377), Zoological Institute, St Petersburg, Russia, 1/46416 (holotype, male, 32 mm), plus 2 female paratypes (none examined).

Description. Body length of figured male 34 mm. Body 1.2 times as long as greatest width (at coxae 3). Dorsal surface smooth. Head, anterolateral margins convex and continuous with anterior margin of pereonite 1; maximum width between anterolateral corners 1.1 times as wide as span between lateral margins of eyes; head without paired processes on transverse ridge at bases of antennae 1, with pair of bilobed tubercles between anterior part of eyes, with acute median posterior tubercle extending past pereonite 1, with obscure lobes lateral to median posterior tubercle. Pereonite 1 of male, lateral margin gently sinuous, 1, lateral margin upturned over anterior half, with sharply-crested submarginal ridge parallel to margin, dorsal surface with oblique transverse ridge reaching near margin. Coxal dorsal plate 2 of male 0.5 times as long as half pereonal tergite 2 width (following plates increasing in length); plate 4 of male as long as half pereonal tergite 4 width; plate 6 of male extending beyond tip of pleotelson by 0.3 times middorsal length of pleotelson; pleonal epimeron 2 of male 0.9 times length of pleotelson; pleonal epimeron 3 of male 0.8 times length of pleotelson; pleonal epimera 2 and 3 with acute apices.

Antenna 1 peduncle articles 3+4 as long as article 2 (anterior margin); flagellum with about 54 articles, at least 3 times as long as peduncle article 3+4 (in male), reaching anterior margin on pereonite 4. Antenna 2 peduncle article 5 1.25 times as long as article 4; flagellum of 18 articles, at least 1.2 times as long as peduncle article 5.

Pereopod 1 propodus 2.2 times as long as greatest width. Pereopod 2 palm dorsal length 2.2 times greatest width, straight, sharply angled at free proximal margin, with 28 spiniform setae surrounding an oval palm. Pereopod 5 of male basis 5 times as long as greatest width, with a keel on the extensor margin, more prominent proximally; merus without setae; carpus 5.5 times as long as greatest width; propodus 6.5 times as long as greatest width; dactylus curved, 0.3 times as long as propodus. Pereopod 6 of male merus sparsely setose, carpus 7 times as long as greatest width; propodus 10 times as long as greatest width; dactylus curved, 0.25 times as long as propodus. Pereopod 7 of male carpus 4 times as long as greatest width (at distal end); propodus 4.5 times as long as greatest width, propodus tapering from base, lower margin gently convex; dactylus curved, 0.15 times as long as propodus.

Pleopod 2 endopod with evenly tapering distal angle bearing appendix masculina; appendix masculina 3.8 times as long as straight margin of endopod. Uropodal rami with rounded apices; exopod 0.7 length of endopod.

Female. Pereonite 1, lateral margin of female as in male. Coxal dorsal plate 2 of female 0.5 times as long as half pereonal tergite 2 width; plate 4 of female 0.7 times as long as half pereonal tergite 4 width (following plates increasing in length); plate 6 of female extending beyond tip of pleotelson by 0.3 times middorsal length of pleotelson.

Distribution. Ross Sea, Antarctica; 500– 900 m.

Remarks. The new material is clearly referable to Kussakin’s species but illustrates some variability, mostly attributed to differences between sexes. Males, in different stages of development, range in size from 25 to 34 mm long (figs 1a, b, e). All possess differentiated pereopods 2 and 7 and the smallest lacks an appendix masculina. In the 29-mm specimen, the appendix masculina is only half the length of that in the 34-mm specimen. In all males, the posterolateral oblique rugosity on the pleotelson is poorly developed. Th e head spine of males reaches about half the length of pereonite 2. The 28-mm female has oostegite buds whereas the others, 30–32 mm, are ovigerous. Dorsal coxal plates are slightly shorter in females. In females, the posterolateral oblique rugosity on the pleotelson is a more well-defined ridge than in the male. In two of the females (figs 1c, d), the posterior spine on the head barely reaches the posterior margin of pereonite 1 whereas in the other (fig. 1d) it reaches the posterior margin of pereonite 2.

Kussakin’s illustration (1968: fig. 15) of the male holotype shows a slightly longer coxal plate 6 than in the male figured here.