Austronanus dentatus ( Nordenstam, 1933 ) Nordenstam, 1933

Just, Jean & Wilson, George D. F., 2006, Revision of Southern Hemisphere Austronanus Hodgson, 1910, with two new genera and five new species of Paramunnidae (Crustacea: Isopoda: Asellota), Zootaxa 1111, pp. 21-58 : 35-39

Austronanus dentatus ( Nordenstam, 1933) , comb. nov.

( Fig. 8 )

Paramunna dentata Nordenstam, 1933: 139 –141, fig. 65.

Remarks on type material. Nordenstam (1933: 239) designated ' Male and female, length about 1 mm.' as 'Types', and reported (p. 241) an additional 6 specimens, all from the Swedish Antarctic Expedition 1901–1903, stn 51. We have examined a sample labelled 'Type­777 syntypes' in the Swedish Museum of Natural History. It contains two microvials, one of which is labelled ' Type specimens' and holds 2 males, one without pleopod I. The other holds 4 females, 2 of which are badly damaged lacking the head. We do not know of the whereabouts of the remaining 2 syntypes. All specimens are in a poor state of preservation, being covered with a 'felt' of fine needle­like crystalline precipitate that cannot be physically removed.

In addition to the habitus drawing mentioned (no sex given), Nordenstam (his fig. 65) illustrated the following details: pereopods I and II (female), left antenna (female), right mandible (no sex given), lower lip (no sex given), pleopods I and II (male), operculum (female). We have examined 12 slides in the Swedish Museum of Natural History, all labelled Paramunna dentata n. sp., Type no. 777, Old number 2680, also No. 6123, all from stn 51. All slides are in a poor condition due to drying out, shrinkage and graininess of the medium. Parts are strongly flattened, sometimes distorted, and fine details often cannot be interpreted with certainty. A list of the slides with Nordenstam's annotations in quotation marks (translated from the Swedish) and the results of our scrutiny in square brackets follow. We have numbered the slides from 1 to 12 and inserted the number on the slides. The slides may deteriorate further without professional restoration.

1. '1st pereopod, Ψ', [one pereopod I].

2. 'Mouthparts and pereopod 1, Ψ', [one pereopod I; one pereopod II; the distal part of one antenna; and both mandibles; all in poor condition].

3. 'Mouthparts and 1st pair of pereopods, Ψ', [two pereopods I too poor condition for illustration, but appear similar to pereopod I of slide 2; right mandible, quality too poor for illustration, but appears similar to those of slide 2; one maxilliped and one maxilla 1].

4. '1st pereopod, Ψ; operculum, Ψ', [one pereopod I, too poor condition for illustration, but appears similar to that of slide 2; one pereopod of the series 2–7, and the operculum].

5. 'Left 1st pereopod, Ψ', [one pereopod I badly dried out, not suitable for illustration; it appears similar to that of slide 2].

6. 'Left 2nd pereopod, Ψ', [one pereopod II].

7. 'Pereopods 1 and 2, Ψ', [one pereopod I in very poor condition, not suitable for illustration, it appears similar to that of slide 2; one pereopod II].

8. 'Left pereopods, Ψ', [four pereopods of the series 2–7, all dried out or embedded in shrinkage ridges, none suitable for illustration].

9. 'Maxilla 1 and maxillipeds, Ψ', [all three].

10. 'Left antennula and antenna, Ψ', [nothing; medium strongly evaporated].

11. 'Left 1st pereopod, ɗ; 1st pair of pleopods, ɗ; 2nd pleopod, ɗ', [all three].

12. 'Left 1st pereopod', sex not given, [nothing].

The number and juxtaposition of pereopods I in slides 1–10 indicate that at least four females, and possibly six, are involved, while one male is represented by slide 11. We can only speculate that one of the female mandibles of slide 2 is the one illustrated in Nordenstam's fig. 65c, that the female operculum of slide 4 is the one illustrated in his fig. 65i, and that the male pleopods I and II of slide 11 are those of his fig. 65g and h. The undissected male from the microvial labelled ' Type specimens', possesses pleopods I and II in place. Hence slide 11 must refer to another male, possibly the smaller, dissected male in the same microvial. We consider all slides to form part of the paralectotype material.

We have designated the largest, least damaged female as lectotype. We have studied the outline of its single somewhat flattened pereopod I, but could confirm the presence of only one robust seta on the propodal margin due to damage and precipitate; and for the same reasons, we could not see possible carpal spines among the robust setae. We have, therefore, reproduced Nordenstam’s (1933, fig. 65e) illustration of pereopod I and have based our description on it, except for description of the basis.

Type Locality. Port Williams, Falkland Islands.

Material examined

Lectotype, here designated. Ψ, 1.20 mm, Port Williams, Falkland Islands, 51°40'S 57°42'W, 22 m, sand 3 September 1902, Swedish Antarctic Expedition 1901–1903, stn 51, SMNH type no. 777.

Paralectotypes. Same data as lectotype, SMNH type no. 6135 (ɗ B, 0.90 mm), SMNH type no. 6135 (6 specimens); also 12 slides (see above), all labelled ' Type no. 777, SMNH no. 6123 (Old number 2680).

Description. Body width 0.46 length in female (illustrated female 0.50, flattened and hence broader than other females in material), width 0.60 length in male, widest at pereonite 2 or 3.

Head length 0.70 and 0.75 width (Ψ, ɗ); length posterior to eyestalks 0.92 anterior length in female, 1.1 in male. Frontal margin lobe length 0.47 head length; apex sharply angular in dorsal view. Eyestalks lateral apex somewhat flattened, long axis angling forward at approximately 30°, not extending to lateral margin of pereonite 1.

Pereonite lateral margin 1–4 linear, 5–7 rounded. Pereonite 5 in dorsal view distinctly narrower than pereonites 4 and 6.

Pleon length 0.86 width in female. Pleotelson proximal margin length shorter than lateral margin length. Pleonite 1 width 0.96 distance between uropods, length 0.2 width. Pleotelson anterior margin in dorsal view forming 60° angle with medial axis of pleon; lateral margins denticulate, with 9 and 10 denticles per side (Ψ, ɗ), becoming larger posteriorly; posterior margin in female forming 110 ° angle.

Antennula with 5 articles, articles 1 and 2 combined shorter than eyestalk; article 1 subequal to 2, broader than 2, inflated; article 5 longer than articles 3 and 4 combined.

Antenna article 3 in ventral view distally expanded, lateral distal margin angular, width 2.00 length; article 5 distinctly longer than article 4; flagellum with 7 articles, proximal article 1.2 length of second article.

Pereopod I basis with crenate ridge on anterior margin, length 2.5 width; carpus (from Nordenstam 1933: fig. 55) distal width 1.25 posterior margin length, with 2 denticles proximal to robust setae (1 large, 1 small), with one denticle between robust setae; propodus narrowing distally to insertion of dactylus, with 2 robust setae. Pereopods V–VII coxae lateral margin elongate and projecting; 2 spines on coxa VII.

Male pleopods I lateral lobes distinctly projecting from midlateral margin, width 0.4 distance to midline; distal projection length 0.28 pleopod total length, approximately forming right angle, with pointed apices. Female operculum distal part tapering with concave distolateral margins, width 0.95 length.

Uropods on lateral margin of pleotelson.

Size. Largest female 1.20 mm, largest male 0.95 mm.

Distribution. Falkland Islands, South Atlantic, 22 m.

Remarks. For comparison with the only other species with 5 articles in the antennulae, see Austronanus aucklandensis , above. We place this species in Austronanus with hesitation, see Classification p. 24.

Figures

FIGURE 8. Austronanus dentatus. A, lectotype, female; B, paratype, male B; C, (reproduced from Nordenstam 1933, fig. 65 e). a, antenna; au, antennula; bas, basis; cv, ventral view of head; cx 1, coxa I; l, left; op, operculum; p 1, pereopod I; pe 5 ­ 7, pereonites 5 ­ 7 with coxae; r, right; up, uropod; vv, ventral view. Habitus scale bar: 0.5 mm.