Austronanus glacialis Hodgson 1910

Austronanus glacialis Hodgson, 1910

(Figs 2–5)

Austronanus glacialis Hodgson, 1910: 50, pl. 8, fig. 3.

Not Paramunna serrata (?).– Nordenstam, 1933: 234; Amar & Roman, 1974: 577.

Type fixation. Holotype, manca, by monotypy, NHM 1910.3.18.95.

Remarks on type material. The holotype is a small unnaturally flattened specimen, apparently manca stage 1 (no development of pereopod VII); surfaces are covered with detritus and crystals, but can be seen to be smooth with little or no setation.

Type Locality. McMurdo Sound, Antarctica.

Material examined

Holotype. Manca, 0.7 mm, Winter Quarters, McMurdo Sound, Antarctica, inside 20 fms line [36.5 m], dredge, ii.1902, 'Discovery' coll., NHM 1910.3.18.95.

Other material. Ross Island, McMurdo Sound, Antarctica (positions estimated from map): Winter Quarters, 77°50.7'S 166°39'E, inside 25 fms line [45 m], 'Discovery' coll., NHM 2005.2086 (ovigerous Ψ A, 1.52 mm); Cape Royds, 77°30'S 166°10'E, J. Oliver, 13 Oct. 1974, AM P67051 (preparatory Ψ); Winter Quarters Bay "Dump", J. Oliver, 9 Sept. 1974, AM P67052 (ɗ B, 1.23 mm, plus 2 ɗ), AM P 67054, (42 Ψ, including Ψ specimen C); Cape Armitage, 77°51.4'S 166°41'E, J. Oliver, 8 Sept. 1974, AM P 67053.

Description. Body width 0.43 length in female, width 0.46 length in male, widest in female at pereonite 2 or 3, widest in male at pereonite 3. Head length 0.66 and 0.74 width (ɗ, Ψ); length posterior to eyestalks 0.77 anterior length in female, 1 in male. Frontal margin lobe length 0.37–0.38 head length (n=3); apex broadly rounded in dorsal view, margin adjacent to apex concave, sinuous. Eyestalks apex broadly rounded, long axis angling forward at approximately 30° in female, 40° in male, somewhat flattened laterally in males.

Pereonite lateral margin 1 linear, 2–7 rounded. Pereonite 5 in dorsal view distinctly narrower than pereonites 4 and 6. Pereonite lateral margins 5–7 finely denticulate. Pleon length 1.00 width in female and male. Pleotelson proximal margin length shorter than lateral margin length. Pleonite 1 width 1.0 distance between uropods, length 0.2 and 0.3 width (ɗ, Ψ). Pleotelson proximal margin in dorsal view forming 50° angle with medial axis of pleon; lateral margins denticulate, with 12 denticles per side, increasing in size posteriorly; posterior margin in female forming 100° angle, in male forming 130° angle, posterior margin with fine denticles laterally, grading to smaller denticles posteriorly, none on posterior apex, with 4 denticles each side.

Antennula articles 1 and 2 combined reaching eyestalk apex; article 1 subequal to 2, inflated, broader than 2; 5–6 of subequal length, longer than articles 3 and 4. Antenna article 2 lateral margin with two spines (distal spine largest); article 3 in ventral view quadrate, lateral margin expanded, width 0.63 and 0.70 length (ɗ, Ψ), with crenate flange on lateral and medial margins, lateral flange wider than medial flange, with 1 distolateral spine embedded in crenate margin, article 5 only slightly longer than article 4; flagellum with 7 articles, proximal article 1.5 length of second article.

Pereopod I basis with crenate ridge on anterior margin, length 2.4 width; ischium anterodistal margin with crenate ridge; merus with 2 spines on anterior margin, 1 spine on posterior margin; carpus distal width 0.81 and 0.95 posterior margin length (Ψ, ɗ), with 2 denticles proximal to robust setae, 2 denticles between robust setae, one denticle distal to robust setae; propodus narrowing distally to insertion of dactylus, opposing margin with 1 robust seta, with crenate ridge. Pereopod II basis with crenate ridge. Pereopods V–VII coxae lateral margin denticulate, central spine large, smaller anteriorly and posteriorly.

Male pleopods I lateral lobes distinctly projecting from midlateral margin, width 0.5 distance to midline, with rounded proximal sublobe; distal projection length 0.27 pleopod total length, approximately forming right angle, with pointed apices. Female operculum distal part tapering with concave distolateral margins, width 0.85 length.

Uropods on lateral margin of pleotelson.

Size. Largest female 1.50 mm, largest male 1.20 mm.

Distribution. McMurdo Sound, Antarctica.

Remarks. One of us (GW) has studied the holotype (Fig. 2). Being a manca and in poor condition of conservation, it is not well suited to define Austronanus glacialis and provide the basis for a diagnosis of the genus. The single adult female (Fig. 3 A) reported here from Winter Quarters, McMurdo Sound (NHM 2005.2086), the type locality of A. glacialis, was discovered by us in the large syntype series of Austrimunna rostrata Hodgson, 1910 (now Pagonana rostrata, see Just and Wilson 2004). In addition, we have had at our disposal 46 specimens collected more recently from Winter Quarters, McMurdo Sound. Females of that sample are identical to the female mentioned above. We feel confident that all these specimens represent Austronanus glacialis, and we have based our diagnosis of the genus and description of the type species on this new material.

Austronanus glacialis shares with A. aucklandensis sp. nov. and A. mawsoni a rounded apex of the head and two concavities on the anterolateral margins; but A. aucklandensis has only 5 articles in the antennulae as opposed to 6 in the other two species. Austronanus glacialis differs from A. mawsoni in the more angular shape of antenna article 3 with a distolateral spine (slightly inflated in middle, no lateral spine) and in the posterior margin of pleotelson with 4 or 5 denticles each side (single denticle).