Xigonus patagoniensis ( Winkler, 1994 ) Winkler, 1994

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 : 47-50

Xigonus patagoniensis ( Winkler, 1994) , comb. nov.

( Figs 14–15 )

Paramunna patagoniensis Winkler, 1994: 268 , figs 21–24.

Remarks on type material. The holotype is a heavily dissected female without head. ZMB 4189 and 4190 also listed by Winkler may refer to slides of the holotype that we have not seen. Winkler (1994) listed as paratypes ‘Males and females from stations HA, HZ and HDD, ZMB 4191­4197, and 26931’. In addition, he listed 49 specimens from a variety of stations as additional material. We have examined the holotype (stn HZ), a male labelled paratype without further data, and 18 specimens from stns HZ and HDD. All specimens examined were under a common label marked ‘ Type material’. We consider the male and the 18 specimens to be paratypes. We have not examined the specimens listed by Winkler as additional material.

Material examined

Holotype. Ψ, 1.07 mm (measurement according to Winkler 1994: 268), Chile, Magellan Strait, 51°32.2'S 69°00.7'W, 12 m, grey fine sand, April 1976, V.A. Gallardo, stn HZ, ZMB 26931.

Paratypes. All ZMB 26931. Same data as holotype, stn HZ 2.0.25.F, 1 fully developed Ψ, 12 specimens mostly small juveniles). Chile, Magellan Strait, 52°20.8'S 68°49.0'W, 17– 21 m, (sediment not known), April 1976, V.A. Gallardo, stn HDD.0.25.F, (ΨA, 1.06 mm, one Ψ, 3 juveniles). Chile, Magellan Strait (no further data, but possibly from stn HA), (1 ɗB, 0.76 mm).

Description. Body width 0.38 length in female, 0.36 length in male, widest at pereonite 2 or 3. Head significantly elongate in male, length 0.88 width, 0.80 in female; length posterior to eyestalks 0.76 anterior length in female, 0.92 in male. Frontal margin lobe length 0.25 and 0.33 head length (ɗ, Ψ); apex bluntly angular in dorsal view, margin adjacent to apex linear, not sinuous. Eyestalks lateral apex rounded, globular, long axis angling forward at approximately 30° in female, 20° in male.

Pereonite lateral margin 1 linear, 2–7 rounded.

Pleon length 0.95 width in female, 0.88 width in male. Pleonite 1 width 1.3 and 1.5 distance between uropods (ɗ, Ψ); length 0.16 and 0.21 width (ɗ, Ψ). Pleotelson proximal margin length shorter than lateral margin length. Pleotelson rounded anteriorly, tapering posteriorly; proximal margin in dorsal view forming 55° angle with medial axis of pleon; lateral margins smooth; posterior margin in female forming 100° angle, in male 90° angle (distinctly pointed in male).

Antennula articles 1–2 combined extending beyond eyestalk apex; article 1 length subequal to 2, inflated, broader than 2; 5–6 of subequal length, longer than articles 3–4.

Antenna article 3 in ventral view lateral margin curved, medial margin straight, width 0.45 length; article 5 only slightly longer than article 4; flagellum with 7 articles, proximal article 1.5 length of second article.

Pereopod I coxa with anterolateral lobe visible in dorsal view; basis anterior margin smooth, length 2.0 width; ischium anterodistal margin with robust bulge; merus with row of low rounded tubercles on posterior margin (4 in female A, Fig.15 ); carpus short and broad, near same size as merus, distal width 1.2 posterior margin length, posterior margin with 2 denticles proximal to robust setae, 1 denticle between robust setae; propodus narrowing distally to insertion of dactylus, with 2 robust setae at approximately midlength.

Male pleopods I lateral lobes distinctly projecting from midlateral margin, width 0.4 distance to midline; distal projection length 0.36 pleopod total length, forming approximately 110° angle, with rounded apices. Female operculum ovoid, width 0.90 length.

Uropods ventral to lateral margin of pleotelson, but visible in dorsal view.

Size. Largest female 1.07 mm, largest male 0.76 mm.

Distribution. Magellan Strait, Chile, 12– 21 m.

Remarks. Our rendition of this species differs from Winkler’s (1994, figs 21–24) in some details. Winkler (fig. 21) showed pointed anterior corners of pereonite 1, but did not discriminate between that segment and the protruding coxa of pereopod I; he showed pereonites 5–7 without dorsally visible coxae; and the first pleonite is shown much narrower than in our Fig. 14 A and B.

Figures

FIGURE 14. Xigonus patagoniensis. A, paratype, female A; B, paratype male B. a, antenna; au, antennula; cv, ventral view of head; cx 1, coxa I; mdp, mandible palp; op, operculum; up, uropod. Habitus scale bar for all three: 0.5 mm.

FIGURE 15. Xigonus patagoniensis. A, paratype, female A; B, paratype male B; C, paratype, ovigerous female. p 1, 2, pereopod I, II; pl 1, pleopod I.