Marmachius fortunae, Poore, Gary C. B., 2012

Poore, Gary C. B., 2012, Marmachius, a spectacular new genus of Antarcturidae (Crustacea: Isopoda: Valvifera), Zootaxa 3559, pp. 61-68 : 63-67

Marmachius fortunae n. sp.

( Figs 1–3 )

Antarcturus sp.— Poore, 2001: fig. 1g.

Material examined. Holotype. Australia, Victoria, 85 km S of Point Hicks, 38.5235°S, 149.3517°E, 1984– 1360 m, G.C.B. Poore et al. on RV Franklin, beam trawl, 26 Oct 1988 (stn SLOPE 72), Museum Victoria ( NMV) J16897 (male, 39 mm).

Description. Total body length about 4.7 times as long as greatest width, almost cylindrical. Head with excavate frontal margin; with pair of submedian long spines curving forwards, 1 short and 1 very short sublateral spines on each side; maxillipedal segment with pair of short straight submedian spines, 2 lateral tubercles each side.

Pereonite 1 with pair of submedian long spines curving forwards, 1 median short straight spine, second pair of submedian very short spines, pair of sublateral long spines anteriorly directed and curved, 2 short lateral (supracoxal) spines arranged obliquely on each side, second longer; coxa fused, laterally notched, with 2 tubercles.

Pereonite 2 with pair of proximate submedian short straight spines, pairs of submedian and sublateral long spines curving forward, 1 median short straight spine, followed by pair of submedian very short spines, 2 lateral (supracoxal) short spines set obliquely on each side (second shorter and more dorsal) and with tubercle between, 3 tubercles in oblique row in front of supracoxal spine on each side; coxa with circlet of 4 very short spines laterally; ventral coxal plate with 1 tubercle in midline. Pereonites 3 and 4 with essentially same spine pattern as pereonite 2 except on ventral coxal plates: ventral coxal plate 3 with 2 tubercles on midline, plate 4 with 1 median tubercle and 2 near basis articulation. Pereonite 5 with pair of submedian long spines curving backwards, pair of submedian short spines, 1 lateral (supracoxal) long spine curving backwards and shorter lateral spine anteriorly on each side,1 median short spine; coxa with 1 long spine laterally directed and posterior tubercle, circlet of 3 tubercles; ventral coxal plate with pair of submedian tubercles. Pereonites 6 as pereonite 5 but without median spine. Pereonite 7 as pereonite 6 but without second pair of shorter submedian spines.

Pleonite 1 plus pleotelson 0.2 total body length. Pleonite 1 free; with 1 short lateral spine on each side. Pleonites 2–6 fused to telson, only vague lateral indications of pleonites 2 and 3. Pleonite 2 with pairs of submedian tubercles, sublateral short spines, lateral short spines; pleonite 3 with pairs of long submedian and very long lateral spines. Remaining pleotelson swollen dorsally and laterally and overlapping margin posterolaterally and posteriorly; with 3 pairs of submedian spines, second long; 4 pairs of sublateral spines, first 2 long, third short, and terminal one as long as pleotelson and posteriorly directed; 5 lateral spines, first very long, remaining shorter; and 3 median short spines in row, last pointing posteriorly and longest.

Antenna 1 reaching to middle of article 3 of antenna 2; article 1 with 1 spine on upper margin. Antenna 2 0.9 times as long as body, ratio of lengths of peduncle articles 3–5, flagellum, 1:1.5:2.0:1.3; article 2 with 1 tubercle on upper margin, 2 distal spines; article 3 with 2 spines on upper margin, second much longer, 2 distal spines; article 4 with 2 distal spines; article 5 with 1 distal spine; flagellum of 9 articles; peduncle article 3 with rows of long setae along lower margin, articles 4 and 5 surrounded by scattered long setae.

Pereopod 1 basis with 1 lateral tubercle, distal margin with row of long setae; ischium–carpus with many long setae on flexor margin; propodus mesial face richly setose close to extensor and flexor margins, slightly concave between; dactylus oval in cross-section, setose especially distally, unguis reaching distal margin of carpus.

Pereopod 2, ratio of lengths of basis: carpus: propodus: dactylus 1:2.0:2.5:1.4; basis with 1 lateral spine plus tubercles; ischium, merus and carpus each with 1 distal spine; merus–propodus with long setae along flexor margin, carpus and propodus surrounded by less dense long setae; propodus curved; dactylus 13 times as long as wide. Pereopods 3 and 4 essentially similar to pereopod 2.

Pereopod 5, ratio of lengths of basis: ischium: propodus: dactylus 1:0.6:0.5:0.5; basis with 2 proximal spines, longer than 3 straight spines in row along lateral margin; merus with 1 distal spine; carpus with row of c. 6 short robust setae and stout setae distally on flexor margin; propodus with row of c. 10 sharp robust setae, smaller distally, along flexor margin; dactylus stout, curved. Pereopods 6 and 7 basis similar to pereopod 5 but with 2 proximal spines, longer than 2 straight spines in row along lateral margin; merus with 1 distal spine.

Penial plate elongate, tapering proximally and distally.

Pleopod 1 peduncle with 27 tubercles laterally, c. 20 retinaculae mesially; exopod as long as endopod, 3.8 times as long as wide, with proximomesial lobe, waisted at midpoint; posterior face of exopod with prominent ridge extending over middle third, overlapping mesial edge of groove; lateral edge of groove sharp, mesial edge illdefined; groove ending near tapering distolateral extension terminating in swollen tip with cluster of numerous fine setae.

Pleopod 2 endopod with appendix masculina 1.2 times as long as endopod, with acute apex.

Uropod peduncle with few tubercles; exopod broader than linear endopod, of equal lengths.

Etymology. For Fortuna , the Roman God of Luck, on account of the isopod’s bad luck in finding itself in the path of the trawl and our good luck in finding it in the trash on the trawl deck.

Remarks. The species was illustrated in a line drawing by Poore (2001). Marmachius fortunae differs from the other species of the genus, M. princeps ( Kussakin & Vasina, 1998) collected in the Emerald Basin, between New Zealand and the Macquarie Island ridge, at a depth of 4300 m. While both species are decorated with pairs of long dorsal spines these are more prominent in the new species and curving forward rather than posteriorly as in M. princeps . Each pereonite of M. princeps has two pairs of long spines and others are relatively much shorter; in M. fortunae the more lateral spines are not as relatively diminished. Kussakin & Vasina (1998) did not specifically mention medial spines but their figure shows what could be a short medial spine on at least pereonites 3–5. They specifically stated that the posterior medial spine is very short but it is not in their figure; this spine may be longer in the new species. The pleotelson is more spinose in the new species, pereopods 2–4 appear more elongate while pereopods 5–7 are more compact.

Figures

FIGURE 1. Antarcturus fortunae n. sp. Holotype. The specimen is somewhat damaged; only one of the long posterolateral spines is present and it points laterally and vertically instead of naturally posteriorly (cf. fig. 3).

FIGURE 2. Antarcturus fortunae n. sp. Holotype. p 1, p 2, p 6, left pereopods 1, 2 and 6; p, penial plate; pl 1, pl 2, right pleopods 1 and 2, posterior views. Scale bars = 1 mm, a applies to top and b to bottom row.

FIGURE 3. Antarcturus fortunae n. sp. Holotype. Stylised dorsal view, lateral spines, coxal spines and pleonal sublateral spines full length, median, submedian and pereonal sublateral as ellipses. p 1, p 2, p 6, distal articles of left pereopod 1 (setae not shown), pereopods 2 and 6; pl 1, pleopod 1 in mesial view with peduncle, endopod deflected (left) and posterior face of exopod (right); am, appendix masculina apex; u, uropodal rami. Scale bar = 1 mm (pereopod distal articles only).