Meridiosignum macquariensis, Just & Wilson, 2021

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 : 424-427

Meridiosignum macquariensis sp. nov.

( Figs 14–15 )

Type fixation. Holotype, ♀, AM P76943.—Here designated.

Type locality. Macquarie Island, Australia.

Etymology. The species is named for the type location, Macquarie Island.

Material examined. Holotype, ♀, 1.5 mm. Australia, Macquarie Island, Aerial Cove , 54°29’S, 158°57’E, 3– 4.5 m, fine sediments in cracks and crevices and under rock overhangs, and coarse sediments from small sediment patches on level bottom, stn MA–382, AM P76943.

Paratypes. Same data as holotype, AM P76944 (29 ♀, 20 ♂; T ♂ of 1.3 mm illustrated) . Australia, Aerial Cove , Macquarie Island, 54°29’S, 158°57’E, 5 m, sponges and bryozoans from sheltered base of vertical rock face near cove entrance, Codium dominant alga, J.K. Lowry ( SCUBA), 12 December 1977, stn MA108, NMV J52116 , (2 adult ♀) . Australia, Aerial Cove , Macquarie Island, 54°29’S, 158°57’E, 6 m, red algae on rocks, D.S. Horning ( SCUBA), 2 February 1978, stn MA–384, NMV J52120 (1 ♀) .

Description. Body width 0.55 length in female, 0.53 length in male, widest in female at pereionite 3, widest in terminal male at pereionites 2–3.

Head slightly longer in male than female, length in male 0.5 width, in female 0.58 width; length posterior to eyestalks 2.0 anterior length in male, 1.3 in female. Frontal margin shallow convex, almost straight medially with angular lateral margins adjacent to antennae. Eyestalks in female length 1.7 width, in male 2.5 width, slightly expanded distally, apex rounded, long axis angling forward at approximately 40° in male, 30° in female. Mandible body with single lateral seta at place of normal palp.

Pereionite 1 of terminal male enlarged, sagittal length in terminal male 2.6 pereionite midline length, in female 2.5 midline length; lateral margins rounded, except tiny mid-lateral spine in male; pereionites 2–4 lateral margins concave with rounded anterior and posterior corners; pereionites 5–7 bluntly pointed.

Coxal plate 1 in terminal male with short anterior rounded projection. Coxae otherwise not visible on pereionites 1–4 in dorsal view; coxae 5–7 visible in dorsal view, bluntly pointed with 1 recurved spine on 7.

Pleon length 1.2 width in female, 1.2 in male. Pleonite 1 as wide as distance between uropods, length 0.20 of width (♀), 0.80 and 0.23 respectively (♂); Pleotelson proximal margin shorter than lateral margin, forming 40° angle with medial axis of pleon; lateral margins evenly convex with 9–10 denticles per side; posterior projection forming 70° angle in female, 80° in male, set apart from lateral margins by concavity at level of uropods, apex broadly rounded, with extensive fringe of long setae.

Antennula articles 1–2 combined extending beyond eyestalk apex; article 1 tubular, shorter and slightly broader than 2; article 3 and 6 of equal length, longer than unequally long 4 and 5.

Antenna article 3 tubular, width 0.30 length, article 4 0.85 length of 5; flagellum with 8 articles, proximal article 1.15 length of second article, following articles successively shorter.

Pereiopod I basis length 3.3 width, with crenate ridge on anterior margin; ischium with row of spines on anterior margin; merus with simple setae only; carpus triangular, distal width 0.85 posterior margin length, posterior margin with 2 strong robust setae, with 2 spines proximal to robust setae, 1 spine between robust setae, one spine distal to robust setae; propodus narrowing distally to insertion of dactylus, with 2 robust setae and crenate ridge on opposing margin. Pereiopod II basis with crenate ridge on anterior margin; ischium with row of spines on anterior margin; carpus and propodus with simple setae, except 1 robust seta posterodistally on propodus.

Male pleopods I lateral lobes distinctly projecting from midlateral margin, width 0.40 distance to midline; distal sublobe with tuft of simple setae; distal projection length 0.27 pleopod total length, forming acute angle, with pointed, setiferous apices. Female operculum width 0.70 length, distal part tapering with concave margins, setiferous apex rounded.

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

Size. Largest female 1.5 mm; largest terminal male 1.3 mm.

Distribution. Macquarie Island, Australia, 3– 6 m.

Remarks. Meridiosignum macquariensis sp. nov. shares with M. kerguelensis the configuration of the concave lateral margins with rounded lobes of pereionites 2–4. For differences between the two species see above ( Meridiosignum kerguelensis ).

Figures

FIGURE 14. Meridiosignum macquariensis sp. nov., holotype, ♀ (dorsal and lateral view), except M, paratype, T♂. a, antenna; au, antennula; cvv, head ventral view; up, uropod; 5–7, pereionites 5–7 with coxa. Scale for habitus (both), 0.5 mm.

FIGURE 15. Meridiosignum macquariensis sp. nov., holotype, ♀, except M, paratype, T♂. l, left; md, mandible; op, opercu- lum; p1–2, pereiopods I and II; plt vv, pleotelson ventral view; r, right.