Elasmopus incomptus, Hughes, Lauren E., 2015

Hughes, Lauren E., 2015, Maeridae from the Indo-Pacific: Elasmopus, Leeuwinella gen. nov., Maeropsis, Pseudelasmopus and Quadrimaera (Amphipoda: Crustacea), Zootaxa 4059 (2), pp. 201-256 : 206-211

Elasmopus incomptus sp. nov.

( Figs 6–8 )

Type material. Holotype male, 4.5 mm, dissected, 3 slides, AM P.81496, Swiss Cheese Reef, Norfolk Island, 29°00'23"S, 167°56'50"E, 12 m, brown algae Dictyota sp., 19 May 2008, coll. J.K. Lowry, MI NFK 78. Paratypes 16 specimens, AM P.81483, dive site ‘The Wall’, Nepean Island, Norfolk Island, 29°04'18"S, 167°57'41"E, 10 m, tufted red and brown algae, 15 May 2008, coll. J.K. Lowry, MI NFK 43.

Type locality. Slaughter Bay, Norfolk Island, South Pacific, 29°03'30"S, 167°57'E.

Etymology. Incomptus from the Latin for unadorned, in reference to the relatively plain male gnathopod 2 propodus palm.

Description. Of holotype male, 4.5 mm, AM P.81496.

Head. Eyes ovate; lateral cephalic lobe broad, truncated, with anteroventral notch/slit, corner rounded. Antenna 1 longer than antenna 2; peduncular article 1 with 1 robust seta on posterior margin, flagellum broken; accessory flagellum minute, with 2 articles. Antenna 2 peduncular article 2 cone gland not reaching to end of peduncular article 3; peduncular article 4 shorter in length than article 5; flagellum with 8 articles. Mandible incisor with cuspidate margin; accessory setal row with 4 setae (illustrated side has row damaged with only 1 seta); molar well-developed; palp well developed, 3-articulate; article 1 twice as long as broad, shorter than article 2; article 2 subequal to article 3, with several slender setae; article 3 short (twice as long as broad), weakly falcate, with apical setae and a comb of short robust setae along anterodistal margin. Lower lip inner lobes present, outer lobes with single pair of ducts, mandibular lobes apically subacute. Maxilla 1 inner plate subquadrate, with 2 apical plumose setae. Maxilliped palp propodus with small distomedial flap.

Pereon. Gnathopod 1 coxa anterior margin straight, anteroventral corner produced, rounded, posteroventral corner without notch; merus without posterodistal tooth; carpus 1.5 × as long as broad, length 0.9 × propodus, anterior margin with a few slender setae; propodus medial surface setal comb absent, palm subacute, convex, entire, defined by posterodistal corner, with 1 robust seta. Gnathopod 2 subchelate; coxa posteroventral corner notch absent; basis slender, anterodistal corner subquadrate; merus with rounded distoventral corner; carpus compressed, lobate, projecting between merus and propodus, length 0.9 × breadth; propodusexpanded, with slender medial setal bunch, palm extremely acute without corner, straight, subtriangular distomedial shelf with group of 5 robust setae on shelf, palm 0.4 × length of propodus, subpalmar surface with long subpalmar seam, with posterodistal robust setae; dactylus apically subacute, closing along andreaching end of palm. Pereopods 5–7 basis posterior margin without long slender setae; merus andcarpus not broadened; dactylar ungues simple. Pereopods 5–6 basis expanded, posterior margin straight, minutely crenulate, without long slender setae, posteroventral corner broadly rounded; carpus and propodus with few long, slender setae along anterior margin; dactylus unguis anterior margin without accessory spines. Pereopod 7 basis posterior margin convex, weakly crenulate, posteroventral corner broadly rounded; carpus and propodus with long slender setae along posterior margin.

Pleon. Epimeron 1 posteroventral corner scalloped. Epimeron 2 posteroventral corner notched. Epimeron 3 ventral margin smooth, posteroventral corner scalloped. Urosomite 1 without carina. Uropod 1 peduncle with 1 basofacial seta; inner ramus shorterthan outer ramus. Uropod 2 inner ramus shorter than outer ramus, subequal in length to peduncle. Uropod 3 inner ramus shorter than outer ramus; outer ramus short, length twice breadth, subequal to peduncle,rami distally truncated, with long and short apical robust setae. Telson as long as broad, deeply cleft (80%), lobes abutting, truncated distally, each lobe with 2 long apical robust setae, with 2 pair of lateral plumose setae.

Remarks. Elasmopus incomptus sp. nov. aligns with E. hawaiiensis Schellenberg, 1938 and E. ecuadorensis, Schellenberg, 1936 , based on the male gnathopod 2 propodus palm with dense brush of setae, epimeron 3 posterior margin scalloped, and the shape of the uropod 3 rami. The telson with two long robust setae on each lobe separates E. incomptus sp. nov. from the latter species, where E. hawaiiensis has two short robust setae and E. ecuadorensis has either three long and one short or three long setae on each lobe (following Barnard, 1979). The mandible of the type material has not been figured in full for the latter two species and it could be useful to either separate or show a close affinity to E. incomptus sp. nov. The mandible accessory setal row with only one seta in E. incomptus sp. nov. is unusual for the genus.

Elamopus incomptus sp. nov. is also similar to E. palu Appadoo & Myers, 2003 in the gnathopod 1 carpus length being subequal to the propodus, the form of the gnathopod 2 propodus palm with a subtriangular distal shelf, dense setae along the margin and seam and pereopods 5–7 basis. However, the gnathopod 2 seam and posterior margin of merus and carpus are without robust setae distinguishing E. incomptus sp. nov. The telson has two long apical setae on each lobe in E. incomptus sp. nov. in contrast to one long and one short seta in E. palu . Lastly, E. palu and the closely related E. lapu Myers, 1985 from Fiji have smooth rather than scalloped epimeron 3 posterior margin.

Distribution. South Pacific Ocean: Tasman Sea: Norfolk Island (current study).

Figures

FIGURE 6. Elasmopus incomptus sp. nov. holotype male, 4.5 mm, AM P. 81496, Slaughter Bay, Norfolk Island, South Pacific.

FIGURE 7. Elasmopus incomptus sp. nov. holotype male, 4.5 mm, AM P. 81496, Slaughter Bay, Norfolk Island, South Pacific, scales 0.1 mm.

FIGURE 8. Elasmopus incomptus sp. nov. holotype male, 4.5 mm, AM P. 81496, Slaughter Bay, Norfolk Island, South Pacific, scales 0.1 mm.