Munnogonium falklandicum ( Nordenstam, 1933 )

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 : 428-430

Munnogonium falklandicum ( Nordenstam, 1933)

( Fig. 17 )

Austrosignum falklandicum Nordenstam, 1933: 5 , 244, fig. 67a–d; 278, “Table of Distribution”.— Austrosignum falklandikum Nordenstam, 1933: 244 (species heading). (See below regarding the spelling of the epithet.)

Austrosignum falclandicum Vanhöffen, 1914 .— Menzies, 1962: 50, lapsus calami.

Austrosignum falclandicum Nordenstam, 1933 .— Menzies, 1962: 52, unjustified emendation.

Munnogonium falklandicum ( Nordenstam, 1933) .— Just & Wilson, 2007: table1.

Type fixation. Syntypes, ♂, ♀.—Originally designated as ‘Types’.

Material examined. Syntypes. Preparatory ♀, 1.8 mm ( Nordenstam 1933: fig. 67A, reported as 1.9 mm), 1 slide with pereiopods I–III, Falkland Islands, Port William , 51°40’S, 57°42’W, 22 m, sand, 3 September 1902, Swedish Antarctic Expedition stn 51, SMNH Type-8816. ♂, 1.6 mm, south of West Falkland, on the Burwood Bank, 53°45’S, 61°10’W, 137–150 m, broken shell with stones, 12 September 1902, Swedish Antarctic Expedition stn 59, SMNH Type-8817 .

Description. Body width 0.40 length in female, 0.33 length in male, widest in both at pereionite 3.

Head length 0.65 width (♂), 0.60 (♀); length posterior to eyestalks 1.1 anterior length. Frontal margin broadly rounded without angular lateral margins adjacent to antennae. Eyestalks vestigial, length equaling width, apex a rounded bump, long axis angling forward at approximately 40°.

Pereionite 1 sagittal length in female 1.1 pereionites midline length, 1.8 in male; pereionite 1 lateral margin rounded (male) or apparently linear (female), 2–4 rounded projecting (less so in female), 5–7 rounded; coxal plates 1–7 visible in dorsal view in male, coxae 5–7 visible in female.

Pleon length 1.8 width in female. Pleonite 1 length/width about 1.0; width/distance between uropods 0.84 (♀), 0.80 (♂), longer than pereionite 7 middorsally. Pleotelson slender, laterally convex, lacking inflection between lateral and proximal margins; posterior projection set apart from lateral margins by moderate concavity at level of uropods, apex pointed.

Antennula article 1 tubular shorter than 2, reaching to or extending just beyond pereionite 1 lateral margin, article 2 moderately expanded distally, articles 4–6 of subequal length, all about half length of 3. Antenna (♂) article 3 tubular, width 0.35 length, article 5 distinctly longer than article 4; flagellum with 6 articles, articles 1 and 2 of equal length, longer than distal ones.

Pereiopod I basis anterior margin smooth, length 3.3 width; ischium smooth; carpus oval, posterior margin with fimbriate projection proximal to each of the 2 posterior robust setae; propodus narrowing distally to insertion of dactylus, opposing margin with 2 long simple setae. Pereiopod II carpus and propodus with long slender robust setae on posterior margin, unguis and ventral claw thin, elongate, both longer than dactylus.

Male pleopods I lateral lobes moderately projecting from lateral margin, width 0.3 distance to midline; distal projection length 0.30 pleopod total length, with pointed apices, combined forming acute angle of 60°. Female operculum ovoid, lateral margins without concavity, width 0.70 length; posterior projection bluntly pointed, forming 80° angle.

Uropods dorsal and directly adjacent to lateral margin of pleotelson, protopod absent or hidden.

Size. Largest female 1.8 mm. Largest male 1.6 mm.

Distribution. Falkland Islands. 22– 150 m.

Remarks. In his ‘Localities and Material’, Nordenstam (1933: 245) listed two specimens, a female from stn 51 and a male from stn 59, both designated ‘Type’, hence they are syntypes. We have examined these two specimens together with 3 slides labelled as ‘ Austrosignum falklandicum n. sp. ’ by Nordenstam. The two specimens are in a rather poor condition; the male lacks all pereiopods, and the pleon is twisted and cracked ( Fig. 17 M ); the female ( Fig. 17 F ) lacks one pereiopod I, the other is damaged, all mouthparts are dissected out with some collateral damage to pereionite 1.

Translated from the Swedish, one of the slides is labelled ‘pereiopod 1–3’. Pereiopods II and III can be seen, but pereiopod I are embedded in dried–out matrix and useless for illustration. It is just possible to verify Nordenstam’s illustration (1933, fig. 67c) of 3 robust setae on the carpus. This slide presumably belongs to the syntype female. The second slide is labelled ‘Maxilliped’; nothing could be found. The third slide is labelled ‘Antennae, mandible, upper lip, ♂ st.51’. All parts can be seen, but because both syntypes have antennulae, antennae and in the case of the male the mandibles intact, this slide must represent a specimen not reported by Nordenstam. We cannot know if it represents Austrosignum falklandicum , and we have, therefore, disregarded that slide.

When describing this species, Nordenstam (1933: 244) gave the species heading as ‘ Austrosignum falklandikum n. sp. ’ In the accompanying fig. 67 and also in the contents on page 5, in the table on page 278, and on the slides he used the form ‘ Austrosignum falklandicum n. sp. ’ Menzies (1962) used the species name ‘ Austrosignum falclandicum ’, which is an unjustified emendation. We believe Nordenstam’s intention was to use the name ‘ A. falklandicum ,’ since the locality is the Falkland Islands and the suffix – cum is the proper Latinization.

Munnogonium falklandicum differs from the two species recently described from the east coast of Argentina ( Doti & Roccatagliata 2013, M. quequensis and M. diplonychia ) by not having a setiferous knob on the front margin of the head, by pleonite 1 being longer than pereionite 7, and by having a more slender body. For further discussion, see Doti & Roccatagliata (2013).

Figures

FIGURE 17. Munnogonium falklandicum (Nordenstam, 1933), F, syntype ♀; M, syntype ♂. a, antenna; au, antennula; cvv, head ventral view; md, mandible; op, operculum; p1–2, pereiopods I and II; pl1, pleopod I; up, uropods. Scale for habitus (both), 0.5 mm.