Pentaceration megalomos, Just, Jean, 2011

Just, Jean, 2011, Remarkable Australasian marine diversity: 18 new species in Pentaceration Just, 2009 (Crustacea, Isopoda, Paramunnidae), Zootaxa 2813, pp. 1-54 : 40-43

Pentaceration megalomos sp. nov.

Figures 28–30

Type fixation. Holotype, female, here designated.

Etymology. The epithet combines the Greek μέγάλος (megalos = large) and ώμος (omos = shoulder) alluding to the exceptionally large pereonite 1 ‘shoulders’ of the male.

Material examined. Holotype, Ƥ, 1.9 mm, Australia, Victoria, south of Point Hicks, 38º17.70'S, 149º11.30'E, 400 m, coarse sand, gravel, mud, WHOI sled, M. Gomon et al., RV Franklin, stn SL 40, 24 July 1986, NMV J20070 (with 2 slides).

Paratypes (18 specimens). Same data as holotype, NMV J20069 (3A, 1.9 mm, illustrated). Same data as holotype, NMV J60998 (13 Ƥ, 4 3).

Description (adult female, holotype). Body elongate, slightly tapering from pereonite 2 towards pleon; width 0.35 length, widest between pereonites 2 and 3. Head length 0.25 width; length posterior to eyestalks 0.5 anterior length. Frontal margin middle spine length subequal to pereonite 1 length; lateral spines as long as middle spine, straight to slightly inward curving, diverging at 120°; all 3 spines with denticulate margins. Eyestalks overreaching pereonite 1 with approximately 0.2 of their length, pointing directly laterad, with slight proximal neck, apex distally micro denticulate.

Pereonite 1 lateral margins rounded, denticulate; pereonites 2 and 3 lateral spines diverging at 45°; pereonite 2 with broad pointed marginally denticulate spine as long as 1/3 pereonite width; pereonite 3 with similar spine pointing more backwards; pereonite 4 laterally rounded, nearly smooth; pereonite 5 lateral spine similar to pereonite 2 but of reduced size; pereonite 6 lateral spine more slender than 2 and 3, pointing backwards at 60º from body midline; pereonite 7 subrectangular, without lateral spines. Pereonite 2, 3, 5 and 6 spines with highly irregular marginal denticles.

Pleon length 1.1 width. Pleonite 1 width 0.74 distance between uropods, length 0.13 width. Pleotelson proximal and lateral margins evenly merging, lateral margins broadly rounded, with 12–13 denticles; distal projection triangular at 70°, apex pointed, 0.33 length of entire pleotelson.

Antennula articles 1 and 2 combined reaching to apex of eyestalks; article 1 shorter and slightly wider than 2, tubular; 3 and 4 of equal length, both half length of subequal 5 and 6.

Antenna article 2 in ventral view at least three times length of 1, with mid-lateral bulge; 3 width 0.32 length, with low denticles laterally in distal half; 5 length 2.7 times 4; 6 twice length of 5; flagellum with 9 articles, first and second articles slender of equal length.

Pereopod I basis length 3.2 times width, anterior margin with distal row of broad blunt spines; ischium length 0.63 length of basis, anterior margin with 2 long and 1 short acute spines; merus with single acute spine on anterior margin; carpus oval, distal margin straight, distal robust seta with small translucent flange in front; propodus narrowing distally to insertion of dactylus, with 2 robust setae on opposing margin. Pereopods II–VII slender; propodus with 3 slender robust setae on posterior margin; pereopod II basis anterior margin with row of slender blunt spines in distal third.

Pleopod II (operculum) ovoid with slightly concave distal margins, apex pointed.

Uropods recessed into low protruding cuticle tube with irregular low marginal denticles; endopod length 2.3 times width.

Male (terminal, illustrated). Generally as female, but differing as follows: Lateral frontal head spines slightly longer than in female, diverging at 115°. Pereonite 1 with large bulbous rounded shoulders; pereonites 2 and 3 lateral spines diverging at 35°; pereonite 2–3 and 6 lateral spines longer and more slender than in female. Pereopod I ischium anterior margin with 2 acute spines in bifurcate pattern; carpus irregularly rectangular, margin distal to robust setae strongly concave with rounded translucent flange in front of distal robust seta. Pleopod I lateral sublobes rounded, similar, overlapping, width 0.37 distance to midline; distal projection length 0.32 pleopod total length, forming acute angle, with pointed apices. Pleopod II protopod bluntly rounded distally, lateral margin and dorsolateral surface with simple setae; endopod article 2 (stylet) forming 150° curve. Uropod endopod length 2.5 width.

Males slightly smaller than the one illustrated have bulging pereonite 1 lateral parts, but pereopod I is similar to females.

Size. Largest female, 1.9 mm; largest male, 1.9 mm.

Distribution. Australia, Bass Strait, 400 m.

Figures

FIGURE 28. Pentaceration megalomos sp. nov. H, holotype, Ƥ. M, paratype, 3 A. B, paratype, Ƥ. C, paratype, 3. a, antenna; au, antennula; cv, head view; md, mandible (l left, r right); up, uropod. Habitus scale: 0.5 mm.

FIGURE 29. Pentaceration megalomos sp. nov. H, holotype, Ƥ. All other, paratype, 3 A. P 1, 2, 6, pereopods 1, 2 and 6.

FIGURE 30. Pentaceration megalomos sp. nov. H, holotype, Ƥ. All other, paratype, 3 A. dv, dorsal view; op, operculum; pt, pleotelson, ventral view; pl 1, 2, pleopods 1 and 2.