Meridiosignum kerguelensis ( Vanhöffen, 1914 )

Just, Jean & Wilson, George D. F., 2021, Redescriptions and new species in the ‘ Austrosignum-Munnogonium’ complex sensu Just & Wilson (2007), mainly from the Southern Hemisphere (Crustacea Isopoda: Paramunnidae), Zootaxa 4952 (3), pp. 401-447 : 418-421

Meridiosignum kerguelensis ( Vanhöffen, 1914)

( Figs 10–11 )

Paramunna kerguelensis Vanhöffen, 1914: 574 , fig. 105a, b.—Wolff, 1962: 252.

Metamunna kerguelensis .— Wolff & Brandt, 2000: 130–131.

Meridiosignum kerguelensis .— Just & Wilson, 2007: 3, 18.

not Paramunna kerguelensis ( Chile) . — Menzies, 1962: 47; Wolff, 1962: 252.

Type fixation. Lectotype, ovigerous ♀.—Here selected.

Type locality. Kerguelen, Southern Ocean.

Remarks on type material. Vanhöffen (1914) only illustrated a single female specimen that he referred to as “ type ”; we identified this specimen based on the configuration of the body and a missing flagellum on the antenna. Although Vanhöffen (1914:574) indicated that only 7 specimens were present, 2 vials from Gauss station 5I02 (5 January 1902) were found in the collection, and the vial containing his illustrated female specimen (also illustrated herein) had 8 specimens, 2 of which were mancas. We suspect that he overlooked one of the mancas when counting. Another vial in ZMB 17711 from the same Gauss station 5I02 (date 5 January 1902) contained an ovigerous female and an adult male, both of which are illustrated here.

Material examined. Lectotype, ovigerous ♀, 1.5 mm, drawn “type” of Vanhöffen (1914), Kerguelen , Gauss station 5I02, ZMB 17711.

Paralectotypes. Same data as lectotype, ZMB 32001(adult ♂ illustrated herein, 1.7 mm, 2 ovigerous females, juvenile male, 3 juvenile females, 2 mancas) .

Other material (not listed by Vanhöffen). Kerguelen, Gauss stn 24I02 (ovigerous female) and Gauss stn 15II03 (ovigerous female). AM P60462.

Description. Body ovate, width 0.55 length and widest at pereionite 3 in both sexes. Head length 0.40 width; length posterior to eyestalks in female 0.43 anterior length, 1.3 anterior length in male. Frontal margin shallow convex, almost straight medially with angular lateral margins adjacent to antennae (several denticles on lateral corners). Eyestalks in female length 1.5 width, male length 1.8 width, apex rounded, shaft slightly constricted proximally, long axis angling forward at approximately 30° (♀) and 40° (♂), with 3–6 ocelli.

Pereionite 1 sagittal length in female 2.3 pereionite midline length, 2.6 in male; pereionites lateral margin 1 rounded, 2–3 centrally concave, 4 with anterior lobe followed by small concavity, 5–6 rounded, smooth, 7 pointed with 2 denticles on posterolateral margin.

Pleon length 1.17 width in female, 1.20 width in male. Pleonite 1 width equal to distance between uropods in female, 0.87 in male. Pleotelson laterally convex, lacking inflection between lateral and proximal margins; with 9–10 denticles per side, margins anterior to denticles straight; posterior projection set apart from lateral margins by concavity at level of uropods, forming angle of 70 o, apex broadly rounded, apex and adjacent margins fringed with elongate setae.

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

Antenna article 3 tubular, width 0.35 length, article 5 distinctly longer than 4; flagellum with 8 articles, article 1 distinctly longer than more distal articles.

Mandible molar process distally truncate, triturative surface cylindrical, without anterior spine.

Pereiopod I basis with crenate ridges on anterodistal margin; ischium smooth; merus occasionally with 2 tiny spines on posterior margin (♂); carpus narrowly triangular, distal width 0.72 posterior margin length, posterior mar- gin with small projections at base of robust setae; propodus narrowing distally to insertion of dactylus, with 2 robust setae, opposing margin with fimbriate ridge. Pereiopod II basis with double row of crenate ridges. Coxal plates of pereiopods 1–4 not visible in dorsal view, 5–7 coxae visible in dorsal view, with apical spine.

Pleopod I lateral lobes distinctly projecting from lateral margin, width 0.35 distance to midline; distal projections 0.32 pleopod total length, combined forming acute angle of 60 o with bluntly pointed setiferous apices. Female operculum width 0.70 length, distal part strongly tapering with concave distolateral margins, apex bluntly rounded with single seta on each side.

Uropods dorsal, immediately adjacent to lateral margin of pleotelson; protopod absent or hidden.

Size. Largest female 1.5 mm. Largest male 1.7 mm.

Distribution. Kerguelen Island, Observatory Bay.

Remarks. Of the species with pereionites 2–4 laterally concave with broadly rounded lobes Meridiosignum kerguelensi s ( Vanhöffen, 1914) is most similar to M. macquariensis sp. nov., but the concavity in females is much more pronounced in the latter. Meridiosignum kerguelensis lacks a row of spines or crenation on the anterior margin of ischium of pereiopods I and II, and has a crenate double row rather than the single row of M. macquariensis sp. nov. on the basis of those legs.

Males and females do not show any apparent variation in the body shape, although the front margin is rounder on mancas and small juveniles. Cuticular roughness or “honeycombing” on the pereionites becomes more pronounced with age, and the spines on the coxae of pereiopods V–VII are not present in the juveniles or mancas.

Figures

FIGURE 10. Meridiosignum kerguelensis (Vanhöffen, 1914), A, lectotype, ♀, 5, 6, 7, pereionite 5–7 lateral margins and coxae. B (all other figs.), paralectotype, copulatory ♂; e, eyestalk; pl1, pleopod I, pl2, pleopod II, p1, pereiopod I; p2, pereiopod II; p7 lateral margin and coxa of pereionite 7; ur, uropod. Scale for habitus, 0.5 mm.

FIGURE 11. Meridiosignum kerguelensis (Vanhöffen, 1914), paralectotypes. C, ovigerous ♀, p1, pereiopod I; p2, pereiopod II; op, operculum; md L, left mandible dorsal view with enlargements of incisor process anterior view and molar process medial view; md R, right mandible dorsal view with enlargements of incisor process anterior view and spine row posterior oblique view. B, copulatory ♂, cv, head ventral view; au, antennula; a, antenna. Scale for habitus, 0.5 mm.