Austroniscus Vanhoeffen, 1914

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 : 48-56

Austroniscus Vanhoeffen, 1914

Synonymy: Nannoniscella Hansen, 1916: 84.

Type species: Austroniscus ovalis Vanhoeffen, 1914

Diagnosis

Body flattened and broadened; pereon and pleotelson expanded laterally in flat, marginal flanges. Rostral crest often well developed. Expansions of pereonites 1–4 anteriorly produced. Antennula generally with 6 articles ( A. chelus sp. nov. only with 7 articles), terminal article unspecialised. Pereopod 1 somewhat shorter and distally more robust than in pereopods 2–7; pereopods 5–7 not derived for swimming, with few natatory setae. Pleotelson without postlateral spines; without ventral spines on operculum or pereonites. Operculum rectangular, covering a small part of the ventral surface. Uropods short in relation to pleotelson, hardly projecting above posterior margin; uropods biramous, endo­ and exopodite almost of same length (modified after Hansen 1916, Siebenaller & Hessler 1981, Vanhoeffen 1914).

Species composition (Table 1)

Austroniscus acutus Birstein, 1970 ; Austroniscus chelus sp. nov.; Austroniscus coronatus Schiecke & Modigh Tota, 1976 ; Austroniscus groenlandicus ( Hansen, 1916) ; Austroniscus karamani Birstein, 1963 ; Austroniscus norbi Svavarsson, 1982 ; Austroniscus obscurus sp. nov.; Austroniscus ovalis Vanhoeffen, 1914 ; Austroniscus rotundatus Vanhoeffen, 1914 ; Austroniscus vinogradovi Gurjanova, 1950 .

TABLE 1. Species composition and distribution of the genus Austroniscus Vanhoeffen, 1914 .

Species Locality Position Depth [m] Austroniscus acutus Birstein, 1970 Japan 44°48`N, 156°33`E 5005–6135 Austroniscus chelus sp. nov Weddell Sea, W.­ Antarctica 71°18.61`S, 013°56.12`E – 910–899.6

71°18.73`S, 013°56.12`E

Austroniscus coronatus Schiecke & Modigh­ Gulf of Naples, Mediterra­ not specified 55–200 Tota, 1976 nean

Austroniscus groenlandicus ( Hansen, 1916) W.­ Greenland 64°03`N, not specified 10–132 Austroniscus karamani Birstein, 1963 E.­ Japan, N.­W. Pacific 37°54`N, 141°43.9`E 5005–5495 Material examined

Holotype: 1 Ψ (preparatory, 2.4 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–40991. Paratypes: 16 Ψ (10 preparatory, 3 adult, 3 damaged), ZMH K–40992, 2 Ψ (preparatory) for SEM, ZMH K–40993, 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. Antennula with 7 articles. Left mandible length 1.3 times right mandible length; incisor of right mandible with 5 teeth, of left mandible with 6 teeth; lacinia mobilis with 4 teeth, molar with 11 simple setae. Outer margin of maxilliped with a row of short membranously embedded setae. Exopod of pleopod 4 almost as long as endopod; pleopod 5 length 1.4 times endopod of pleopod 4 length.

Description

Habitus of female holotype ( Figs 1 A, 5A): Body dorsoventrally considerably flattened and broadened ( Fig. 5 A, B), almost twice as long as wide, with few simple setae laterally. Coxae not visible in dorsal view. Pereonites 1–4 with strongly frontally directed laterofrontal margins, tipped with a small spine apically. Pereonite 1 widest, 3.7 times longer than wide, with a spine­like appendix, inserting ventrally, tipped with a small spine and almost reaching anterior margin of the cephalothorax. Pereonites 1–3 increasing, pereonites 4–7 decreasing in length and width distally. Pleotelson 0.23 times body length, 1.8 wider than long, width 0.8 times pereonite 3 width. Posterior margin strongly rounded, anterior dorsal margin straight; dorsal surface smooth. Anus ( Fig. 1 B) covered by anus valves laterally. Uropods inserting closely to the anus valves; uropods and operculum relatively small, anterior ventral margin medially convex.

Cephalothorax almost as wide as long, posterior half covered by pereonites 1–2; rostrum well developed ( Fig. 5 C, D), frontomedial margin of head slightly concave. Antennae inserting frontolaterally in a deep fold between rostral crest and anterolateral, triangular projections; each fold with a single spine medially.

Antennula of female paratype ( Fig. 2 F) 0.13 times body length, with 7 articles. Basal article short, 1.4 times longer than wide, with 5 short broom setae and 2 slender, simple setae distally. Article 2 slender, 4 times longer than wide, with 3 short, simple setae and 1 long broom seta laterally, with 2 long broom setae and 1 short simple seta distally. Articles 3–7 almost of same length, each about 0.25 of article 2 length, width decreasing distally. Article 3 with 1 long broom seta and 1 short simple seta distally. Article 4 with 2 broom setae of different size distally. Article 5 with 1 short simple seta distally. Article 7 with 2 long and 4 short simple setae terminally.

Antenna length ( Fig. 2 G) almost of body length, with 6 peduncular and 18 flagellar articles. Peduncular articles 1–4 short; article 2 with 1 short spine laterally, article 3 with a large spine almost as long as article 4 ( Fig. 5 D). Articles 5–6 long and slender, article 5 about 7.5 times longer than wide, with 2 robust setae, 1 broom seta and 2 small simple setae laterally, with a single seta (broken off) distally. Article 6 about 11.3 times longer than wide, with 1 short spine and 3 short simple setae laterally, with 3 broom setae and 4 slender setae of different sizes distally. Flagellar article 1 longest, about 0.3 times peduncular article 6 length, 5.2 times longer than wide, with 4 simple setae laterally. Flagellar articles 2–16 of similar length, width decreasing distally, each article with 1–3 short simple setae distally. Articles 17–18 somewhat shorter, article 17 with 5 simple setae, article 18 with 7 long, slender setae terminally.

Left mandible ( Fig. 2 B) length 1.3 times right mandible ( Fig. 2 A) length. Mandibular palp of left mandible lost during dissection; palp of right mandible long and robust, overlapping tip of incisor about a half, consisting of 3 articles; article 1 shortest, with 2 simple setae distally; article 2 1.5 times longer than article 1, 3 times longer than wide, with 3 simple setae distally; terminal article tapering distally, with 9 short simple setae ventrally, with 3 robust setae terminally. Incisor of right mandible with 5 teeth, of left mandible with 6 teeth. Lacinia mobilis of left mandible with 4 teeth and 1 short setule. Setal row of right mandible with 12 setae; distal seta dentate and robust, dentation decreasing proximally. Setal row of left mandible with 14 setae; distal setae 1–3 most robust and dentate, proximal setae more slender. Molar of right mandible lost, of left mandible triangular, with 11 simple setae distally.

Outer endite of maxillula ( Fig. 2 C) with 9 robust spine­like setae and 16 slender setae distally. Outer margin with 3 long, slender and 1 short seta. Inner endite half length of outer endite, with 12 fine setae distally. Maxilla ( Fig. 2 D) outer margins of lateral and inner endites with several long setules. 3 strong setae of varying length on lateral and medial endites. Distal margin of inner endite with numerous long setules. Surface of inner endite with some short setules.

Maxilliped epipodite ( Fig. 2 E) triangular, slender, 4.1 times longer than wide, reaching to mid of palpal article 2. Palpal article 1 short, 2.3 times wider than long, with 1 simple seta distally. Article 2 longest, 2.4 times longer than article 1, almost quadrangular, with 1 simple seta distally. Palpal article 3 length 1.8 of article 1 length, 1.4 times longer than wide, with 2 robust sensory setae and 6 somewhat longer, slender setae distally. Article 4 about 0.75 of article 1 length, as long as wide, with a projection almost reaching tip of article 5, with 5 slender setae of varying size distally. Article 5 as long as fourth, twice as long as wide, with 6 slender setae terminally. Endite´s inner margin with numerous short setae, membranously embedded; distal margin with some dentate setae. Protopod rectangular, about 3 times wider than long.

Pereopod 1 ( Fig. 3 A) more robust than pereopods 2–7. Basis 3.25 times longer than wide, with 1 broom seta, 4 short simple setae dorsally and 7 simple setae of varying size ventrally. Ischium length almost half of basis length, 2.4 times longer than wide; with 2 simple setae distodorsally and 3 simple setae ventrally. Merus length 0.6 times ischium length, 1.6 times longer than wide; with 1 distal simple seta dorsally and ventrally. Carpus length twice merus length, 3.6 times longer than wide; with 1 seta dorsally, ventral margin slightly concave, with 5 simple setae of varying size and 1 more robust seta distally. Propodus length 0.8 times carpus length, 4 times longer than wide; with 5 slender simple setae dorsally, increasing in length distally, with numerous small setae, membranously embedded, and 6 somewhat longer setae in between ventrally. Dactylus nearly half of carpus length, 2.6 times longer than wide; with 2 small, slender setae medially. Unguis with 1 robust cuspidate seta dorsally and with 2 slender, somewhat longer setae ventrally.

Basis of pereopod 2 ( Fig. 3 B) 3.6 times longer than wide; with 6 broom setae and 2 small simple setae dorsally, with 1 long and robust seta at distal margin ventrally. Ischium half of basis length, 2.25 times longer than wide; with 1 robust simple seta dorsally and 3 short simple setae ventrally. Merus length 0.7 times ischium length, 1.8 times longer as wide, with 1 robust unequally bifid seta dorsally, with 1 long seta ventrally. Carpus length 2.8 times merus length, 5.6 times longer than wide; with 2 stout unequally bifid setae dorsally, with 1 slender seta (broken off) and 1 long broom seta distally, with 3 stout unequally bifid setae ventrally and with 2 robust simple setae and 1 slender simple seta distally. Propodus length 0.8 times carpus length, 7 times longer than wide, with 2 simple setae dorsally and with 5 robust unequally bifid setae and 1 slender, simple seta ventrally. Dactylus length 0.4 times propodus length, 4.6 times longer than wide, with 3 thin, simple setae medially. Unguis with 2 robust cuspidate setae and 1 somewhat longer simple seta in between.

Basis of pereopod 3 ( Fig. 3 C) 4.3 times longer than wide; with 5 broom setae of varying size and 4 small simple setae dorsally and with 6 short simple setae and 1 long slender seta ventrally. Ischium length half of basis length, 2.6 times longer than wide; with 3 simple setae dorsally decreasing in size distally, with 3 simple setae of varying size and 1 short broom seta ventrally. Merus length 0.7 times ischium length, 2.1 times longer than wide; with 1 long seta ventrally and dorsally. Carpus length 2.1 times merus length, 5 times longer than wide; with 1 robust seta, 2 slender setae and 1 long broom seta dorsally, with 3 stout unequally bifid setae ventrally. Propodus length nearly carpus length, 7.8 times longer than wide, with 1 unequally bifid seta, 2 simple setae and with 1 broom seta dorsally, with 4 stout unequally bifid setae ventrally, decreasing in length distally. Dactylus length 0.4 times propodus length, 4.5 times longer than wide; with 3 thin, simple setae medially. Unguis with 2 robust cuspidate setae and 1 slender seta in between.

Basis of pereopod 4 ( Fig. 3 D) 4.1 times longer than wide; with 4 broom setae and 7 small simple setae dorsally, with 9 simple setae of varying size ventrally. Ischium length 0.6 times basis length, about 2.8 times longer than wide; with 2 robust simple setae dorsally, with 2 small broom setae and 1 short simple seta ventrally. Merus length 0.6 times ischium length, twice as long as wide; with 1 long seta ventrally. Carpus length 2.4 times merus length, 5.6 times longer than wide, with 1 long broom seta and 2 somewhat shorter simple setae distodorsally, with 3 stout unequally bifid, 2 robust and 1 slender setae ventrally. Propodus length almost carpus length, 7 times longer than wide; with 4 short, simple setae dorsally and with 2 broom setae distodorsally, with 5 stout unequally bifid setae and 3 slender, simple setae ventrally. Dactylus length 0.4 times propodus length, 6 times longer than wide; with 3 thin, simple setae medially. Unguis with 2 robust cuspidate setae.

Basis of pereopod 5 ( Fig. 4 A) 3.1 times longer than wide; with 5 simple setae dorsally and with 1 long broom seta and 1 very short simple seta ventrally. Ischium length 0.7 times basis length, 2.4 times longer than wide; with 2 short simple setae dorsally and with 1 long robust seta and 2 somewhat shorter simple setae ventrally. Merus length about half of ischium length, 1.3 times longer than wide; with 1 slender, simple seta dorsally and with 1 robust, long seta distoventrally. Carpus length 2.8 times merus length, 3.8 times longer than wide; with 3 robust unequally bifid setae and 1 slender seta (broken off) dorsally, with 3 robust unequally bifid setae, 1 slender, simple seta and 1 broom seta ventrally. Propodus length 0.9 times carpus length, 7.2 times longer than wide; with 1 simple seta and 2 unequally bifid setae dorsally, with 1 broom seta and 2 short, simple setae distoventrally. Dactylus length 0.3 times propodus length, 4.3 times longer than wide; with 3 slender setae medially; unguis with a robust cuspidate seta and 1 slender simple seta.

Basis of pereopod 6 ( Fig. 4 B) broken off, 3.7 times longer than wide; with 5 slender, simple setae ventrally. Ischium length 0.7 times basis length, 3.2 times longer than wide; with 2 slender simple setae dorsally. Merus length 0.4 times ischium length, 1.5 times longer than wide; with 2 robust long setae distodorsally. Carpus length 2.9 times merus length, 3.8 times longer than wide; with 2 unequally bifid setae, 1 simple short seta and 2 broom setae (1 broken off) dorsally, with 3 unequally bifid setae of varying size ventrally. Propodus length 0.9 times carpus length, 7.1 times longer than wide; with 2 simple setae distodorsally, with 3 robust unequally bifid setae seta ventrally. Dactylus length 0.4 times propodus length, 4.8 times longer than wide. Unguis with 1 robust cuspidate seta, and 3 slender setae of similar size.

Basis of pereopod 7 ( Fig. 4 C) 3.8 times longer than wide; with 5 simple setae dorsally and with 6 simple setae of varying size ventrally. Ischium length 0.7 times basis length, 3.25 times longer than wide; with 2 robust, long setae dorsally and with 2 short simple setae ventrally. Merus length 0.4 times ischium length, 1.3 times longer than wide; with 2 robust long setae distodorsally and with 1 short simple seta distoventrally. Carpus length 3.3 times merus length, 4.4 times longer than wide; with 2 unequally bifid setae and 1 broom seta dorsally, with 3 robust unequally bifid setae and 1 short simple seta ventrally. Propodus length 0.8 times carpus length, 8.6 times longer than wide; with 1 broom seta and 1 short simple seta dorsally, with 3 robust unequally bifid setae ventrally, decreasing in size distally. Dactylus length 0.4 times propodus length, 5.3 times longer than wide. Unguis with 1 robust cuspidate seta and 1 slender seta ventrally; with a small ventral appendix.

Pleopod 2 (operculum, Fig. 4 D) 1.6 times longer than wide, ventral surface with fissures. Lateral margin with few short setules, posterior margin with numerous (> 30) long, slender setae.

Protopodite of pleopod 3 ( Fig. 4 E) rectangular, almost as long as wide, length 0.6 times endopodite length. Exopodite almost as long as endopodite, 2.5 times longer than wide, with 3 simple setae of varying length. Endopodite 1.5 times longer than wide, with 1 short and 2 long plumose setae distally.

Protopodite of pleopod 4 ( Fig. 4 F) short, 3.8 times longer than wide. Exopodite slender, 5 times longer than wide, with 1 long robust plumose seta distally. Endopodite 1.8 times longer than wide.

Pleopod 5 ( Fig. 4 G) small oval lobe, 1.4 times longer than endopodite of pleopod 4, almost twice as long as wide. Inner margin straight, outer margin strongly rounded, without setation.

Uropods ( Fig. 1 C) biramous. Protopodite trapezoid, 1.7 times longer than wide, as long as exopodite, with 5 robust setae of varying size. Exo­ and endopodite almost of same length. Exopodite length 0.9 times endopodites length, 4.1 times longer than wide, with 6 setae of varying size terminally. Endopodite 3.9 times longer than wide, with 2 robust simple setae and 1 short broom seta laterally, with 5 broom setae of varying size, 2 simple setae and 2 setae (broken off) terminally.

Type locality

Eastern Weddell Sea, Kapp Norvegia.

Distribution

The species is only known from type locality.

Remarks

Austroniscus chelus sp. nov. is most similar to Austroniscus obscurus sp. nov.; the latter can be distinguished from the first species by the following characters ( Table 2 ): antennula with 6 articles; incisor of the right mandible with 6, of left mandible with 5 distinct teeth; lacinia mobilis 3­lobed, molar of the left mandible medially notched yielding numerous small setules; fourth palpal article without appendix; dactylus of pereopods 5 and 7 with ventral appendices distally; protopodite of pleopod 3 only reaching one third of endopodite length; pleopod 5 smaller than pleopods 3 and 4.

The new species can be distinguished from Austroniscus ovalis Vanhoeffen, 1914 by the following characters ( Table 2 ): antennula with 7 articles; rostrum not as deeply vaulted as in A. ovalis ( Fig. 11 C, D); first pereonite anterofrontally directed and tipped with a small spine ( Figs 5 D, 11C).

Figures

FIGURE 1. Austroniscus chelus sp. nov.; A – B, holotype female (ZMH K – 40991); A, dorsal view. B, Plt ventrally. C, paratype female (ZMH K – 40992), Urp. Scale bar: A – B = 1 mm, C = 100 µm.

FIGURE 2. Austroniscus chelus sp. nov., paratype female (ZMH K – 40992); A, rMd. B, lMd. C, Mx 1. D, Mx 2. E, Mxp. F, A 1. G, A 2. Scale bar = 100 µm.

FIGURE 3. Austroniscus chelus sp. nov., paratype female (ZMH K – 40992); A – D, P 1 – 4. Scale bar = 100 µm.

FIGURE 4. Austroniscus chelus sp. nov., paratype female (ZMH K – 40992); A – C, P 5 – 7. D, Plp 2 (operculum). E – G, Plp 3 – 5. Scale bar = 100 µm.

FIGURE 5. Austroniscus chelus sp. nov., paratype female (ZMH K – 40993), SEM; A, habitus, dorsal view. B, habitus, lateral view. C, cephalothorax, dorsal view. D, cephalothorax frontally.

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.