Austroniscus obscurus, Kaiser, Stefanie & Brandt, Angelika, 2007

Kaiser, Stefanie & Brandt, Angelika, 2007, Two new species of the genus Austroniscus Vanhoeffen, 1914 (Isopoda: Asellota: Nannoniscidae) from the Antarctic shelf, Zootaxa 1394, pp. 47-68 : 58-64

Austroniscus obscurus sp. nov.

( Figs 6–9 )

Material examined

Holotype: 1 Ψ (adult, 1.9 mm), eastern Weddell Sea, 71°18.61`S, 013°56.12`E – 71°18.73`S, 013°56.12`E, PS ANT XXI/2, Station 232–1, 910– 899.6 m, ZMH K–40994.

Paratypes: 3 Ψ (2 preparatory, 1 damaged), ZMH K–40995, 1 Ψ ( SEM specimen), preparatory, ZMH K– 40996, same station as holotype.

Diagnosis

Pereonite 1 strongly frontally directed, with a spine­like appendix inserting ventrally, tipped with a small spine and almost reaching anterior margin of the cephalothorax. Posterior half of cephalothorax half covered by pereonites 1–2. Incisor of right mandible with 6 teeth, left mandible with 5 teeth. Lacinia mobilis with 3 teeth. Unguii of pereopods 5 and 7 with 1–2 robust ventral spines proximally.

Description

Habitus of female holotype ( Figs 6 A, 9A–B) similar to A. chelus sp. nov.

Antennula length ( Fig. 6 B) 0.2 times body length, with 6 articles. Article 1 broad, 1.4 times longer than wide, with 3 broom setae (one broken off) and 3 slender simple setae of varying size. Article 2 as long as first, 3.7 times longer than wide; with 4 long broom setae and 2 small simple setae distally. Articles 3–4 about 1.5 times longer than wide, with 1–2 small simple setae distally. Article 5 elongated, 4 times longer than wide. Article 6 as long as article 3, with 2 long and 2 somewhat shorter simple setae terminally.

Antenna ( Fig. 6 C) long and slender, almost as long as body. Peduncular articles 1–4 short; article 3 with a large spine almost as long as article 4. Peduncular articles 5–6 long and slender; article 5 about 5.3 times longer than wide, with some short setae and 2 robust setae laterally, with 1 broom seta and 2 simple setae of varying size distally. Article 6 about 8.3 times longer than wide, with some short setae and 1 small seta laterally, with 5 broom setae and 5 simple setae of varying size distally. Distal 21 flagellar articles tapering in width and length distally. Flagellar article 1 longest, length 0.25 times peduncular article 6 length, 3.7 times longer than wide. Flagellar articles 1–20 with 1–5 setae distally; terminal article with 6 long and slender setae.

Right and left mandible ( Fig. 6 E, F) with long mandibular palp, overlapping incisor about one quarter. Article 1 shortest, in right mandible with 1 simple seta. Article 2 longest, medially and in left mandible also laterally with a row of short setules, with a single, more robust seta distally. Article 3 tapering in width distally, very slender in right mandible; ventral margin with some small, robust setae, with 1–3 somewhat longer robust setae terminally. Incisor in right mandible well pronounced, with 6 distinct teeth; in left mandible incisor short (damaged in this specimen), with 5 distinct teeth. Setal row of right mandible with 17 setae; distal setae most robust and dentate, expressivity of this dentation decreasing proximally; in right mandible setal row with 8 robust setae and 11 slender setae in between. Molar triangular, in right mandible with 4 simple and 4 serrated setae. Molar of left mandible with 11 fine setae laterally, apical margin notched, yielding several small setules.

Outer endite of maxillula ( Fig. 6 G) with 10 spine­like setae followed by 8 slender ones distally. Outer margin with 7 slender setae, inner margin with 4 short setae. Inner endite about half as long as outer endite, with 15 simple setae distally, outer margin with 3 short setae.

Maxilla ( Fig. 6 H) outer margin of lateral endite with few slender setae and with 3, medial endite with 4 strong setae of varying size distally. Outer margin of inner endite with numerous long, slender setae, inner margin with few slender setae; distal margin with few fine and 2 robust, somewhat longer setae. Surface of inner endite with few short setules.

Left and right maxilliped ( Fig. 6 D) connected by 3 retinacula. Epipodite triangular, slender, 4.5 times longer than wide, reaching middle of palpal article 2. Palpal article 1 short, 2.7 times wider than long, outer margin with some small setules. Article 2 longest, 2.3 times longer than wide, almost quadrangular, with 1 simple seta laterally. Article 3 twice as long as article 1, about 1.25 times longer than wide, notched distally, with 7 slender setae laterally. Article 4 as long as article 1, 1.5 times longer than wide, without appendix, with 2 simple setae distally. Article 5 as long as fourth, half of article 4 width, with 8 slender setae. Endite’s inner margin with numerous slender setae; distal margin with several dentate setae, membranously embedded. Protopodite rectangular, width 1.6 times length.

Pereopod 1 ( Fig. 7 A) more robust than pereopods 2–7. Basis 3.7 times longer than wide; with 2 small broom setae and 3 short, simple setae dorsally, with 1 very long and 2 short broom setae and 3 simple setae ventrally. Ischium length half of basis length, twice as long as wide; with 1 slender and 1 robust seta dorsally and with 2 short slender setae ventrally. Merus length 0.7 times ischium length, 1.6 times longer than wide; with 2 robust setae distodorsally and with 2 slender setae distoventrally. Carpus length 2.2 times merus length, 3.5 times longer than wide; with 1 seta mediodorsally, ventral margin slightly concave, with 3 slender setae and 1 robust seta laterally, with 1 robust unequally bifid seta distally. Propodus length 0.7 times carpus length, 3 times longer than wide; with 1 long, slender seta mediodorsally, with a fringe of short setae, membranously embedded, and 1 robust unequally bifid seta ventrally and with 2 setae of varying size distally. Dactylus length 0.7 times propodus length, 4.3 times longer than wide; with 3 slender setae medially. Unguis with 2 robust, cuspidate setae, ventral one a bit shorter and more slender with 2 slender setae of similar size in between.

Basis of pereopod 2 ( Fig. 7 B) 3.6 times longer than wide; with 1 broom seta and 1 simple seta dorsally; with 1 simple seta distoventrally. Ischium length half of basis length, about 2.4 times longer than wide; with 1 simple seta dorsally. Merus half of ischium length, 1.8 times longer than wide. Carpus length 3.3 merus length, 5.8 times longer than wide, with 1 long broom seta and 1 robust simple seta dorsally, with 4 robust unequally bifid setae and 1 robust simple seta ventrally. Propodus length 0.9 times carpus length, 8.4 times longer than wide; with 3 slender simple setae dorsally and with 1 simple seta medially, with 1 robust simple seta ventrally. Dactylus length 0.4 times propodus length, 6 times longer than wide; with 3 slender setae of varying size ventrally. Unguis with 1 robust cuspidate seta and with 2 slender setae ventrally.

Basis of pereopod 3 ( Fig. 7 C) 3.8 times longer than wide; with 3 broom setae of varying size and 3 simple setae dorsally, with 4 short setae and 1 robust simple seta ventrally. Ischium length half of basis length, 2.4 times longer than wide; with 1 robust simple seta dorsally. Merus length 0.7 times ischium length, 1.9 times longer than wide; with 1 long, robust seta distodorsally and 1 slender simple seta ventrally. Carpus length 2.3 times merus length, 4.9 times longer than wide; with 1 long broom seta distodorsally, with 3 robust unequally bifid setae ventrally (2 broken off) and with 4 setae of varying size distoventrally. Propodus length 0.9 times carpus length, 6.5 times longer than wide; with 3 slender setae dorsally and 1 simple seta distally, with 3 robust unequally bifid setae and 1 simple seta ventrally. Dactylus length 0.5 times propodus length, 5.1 times longer than wide; with 4 slender setae of varying size medially. Unguis with 1 robust cuspidate seta and with 2 slender setae ventrally.

Basis of pereopod 4 ( Fig. 7 D) 4.5 times longer than wide; with 1 simple seta dorsally and with 1 broom seta and 2 short simple setae ventrally. Ischium length half of basis length, 2.8 times longer than wide; with 1 slender simple seta ventrally. Merus half of ischium length, 1.7 times longer than wide; with 1 long, robust seta dorsally and 1 more slender seta distoventrally. Carpus length 2.7 of merus length, 5.9 times longer than wide; with 1 slender seta distodorsally and with 2 very small setae and 1 robust simple seta ventrally. Propodus length 0.8 times carpus length, 8.8 times longer than wide; with 2 slender simple setae distodorsally and with 3 slender simple setae ventrally. Dactylus length 0.4 times propodus length, 5 times longer than wide; with 3 slender setae of varying size medially. Unguis with 1 robust cuspidate seta and with 1 slender simple seta ventrally.

Basis of pereopod 5 ( Fig. 8 A) 3.2 longer than wide; with 4 short simple setae dorsally and 3 long broom setae and 2 slender simple setae ventrally. Ischium length 0.6 basis length, 2.5 times longer than wide; with 2 dorsal and 2 ventral setae of varying size. Merus half of ischium length, 1.6 times longer than wide; with 1 small simple seta dorsally and 2 robust, long setae distoventrally. Carpus length 2.9 times merus length, 4.7 times longer than wide; with 1 long broom seta distodorsally and with 1 robust unequally bifid seta and 2 slen­ der simple setae ventrally. Propodus length 0.9 times carpus length, 7 times longer than wide; with 2 broom setae and 1 short unequally bifid seta dorsally, with 3 robust unequally bifid setae ventrally. Dactylus length 0.45 times propodus length, 4.8 times longer than wide; with 4 slender simple setae medially and with 1 appendix ventrally. Unguis with 1 robust cuspidate and 1 slender seta ventrally.

Pereopod 6 is missing.

Basis of pereopod 7 ( Fig. 8 B) 4 times longer than wide; with 2 small simple setae dorsally and with 3 slender setae of varying size ventrally. Ischium length 0.6 times basis length, 2.8 times longer than wide; with 2 slender simple setae each dorsally and ventrally. Merus length 0.4 times ischium length, 1.3 times longer than wide; with 2 robust, long setae distodorsally and 2 short setae distoventrally. Carpus length 4.5 times merus length, 4.9 times longer than wide; with 1 long broom seta and 1 short simple seta distodorsally, with 1 short unequally bifid and 1 simple seta ventrally and with 2 robust setae distoventrally. Propodus length 0.9 times carpus length, 7.7 times longer than wide; with 1 robust and 1 slender simple seta of different size dorsally, with 2 robust unequally bifid setae and 2 slender simple setae ventrally. Dactylus length 0.4 times propodus length, 4.5 times longer than wide; with 3 slender simple setae medially and with 2 appendices of different size ventrally. Unguis with 1 robust cuspidate and 1 slender seta.

Pleopod 2 (operculum, Fig. 8 C) 1.4 times longer than wide. Ventral surface with fissures; posterior margin with several (<30) long, slender setae.

Pleopod 3 protopodite ( Fig. 8 D) rectangular, length 0.3 times endopodite length. Exopodite relatively long and slender, length 0.75 times endopodite length, about 4 times longer than wide, with 1 long, slender seta. Endopodite 1.2 times longer than wide, with 3 plumose setae distally.

Protopodite of pleopod 4 ( Fig. 8 E) 2.4 times longer than wide, length 0.25 times endopodite length. Exopodite slender, about 5 times longer than wide, outer margin with several small setules, with 1 long, robust seta distally. Endopodite 1.4 times longer than wide, tapering distally.

Pleopod 5 ( Fig. 8 F) small oval lobe without setation; shorter than endopodites of pleopods 3 and 4, about 1.7 times longer than wide.

Uropods ( Fig. 8 G) biramous; protopodite trapezoid, as long as exopodite, 1.6 times longer than wide, with 2 slender setae distally. Exo­ and endopodite almost of same length, about four fifths of endopodite length, 4.2 times longer than wide, with 2 broom setae and 1 simple seta terminally. Endopodite 3.9 times longer than wide, with 4 broom setae and 6 simple setae of varying size terminally.

Type locality

Eastern Weddell Sea, Kapp Norvegia.

Distribution

The species is only known from type locality.

The new species also resembles Austroniscus ovalis Vanhoeffen, 1914 and differs from that species as follows: the rostrum not as deeply vaulted as in A. ovalis ( Fig. 11 C, D); first pereonite anterofrontally directed and tipped with a small spine ( Figs 9 A, 11C); second article of antennula with 4 long broom setae.

Figures

FIGURE 6. Austroniscus obscurus sp. nov.; A, holotype female (ZMH K – 40994), habitus, dorsal view. B – H, paratype female (ZMH K – 40995); B, A 1. C, A 2. D, Mxp. E, rMd. F, lMd. G, Mx 1. H, Mx 2. Scale bar: A = 1 mm; B – H = 100 µm.

FIGURE 7. Austroniscus obscurus sp. nov., paratype female (ZMH K – 40995); A – D, P 1 – 4. Scale bar = 100 µm.

FIGURE 8. Austroniscus obscurus sp. nov., paratype female (ZMH K – 40995); A – B, P 5 and 7. C, Plp 2 (operculum). D – F, Plp 3 – 5. G, Urp. Scale bar = 100 µm.

FIGURE 9. Austroniscus obscurus sp. nov., paratype female (ZMH K – 40996), SEM; A, cephalothorax frontally. B, habitus, dorsal view.

FIGURE 11. Austroniscus ovalis Vanhoeffen, 1914, paratype female (BENDEX, ZMH K – 41123), SEM; A, habitus, dorsal view. B, Plt, ventral view. C, cephalothorax frontally. D, cephalothorax dorsally.