Eualus oreios Nye, 2013, sp. nov.

Eualus oreios sp. nov.

(Figs. 4–6)

Material examined. Holotype: female, CL 6.2 mm. Coral Seamount, southwest Indian Ocean; co-ordinates: 41° 22.38S 42° 54.64E; water depth: 732 m [OUMNH.ZC.2013-01-003]. Collected on the 66th voyage of RRS ‘James Cook’, November 2011.

Description. Body (Fig. 4) moderately slender, integument glabrous.

Rostrum (Figs. 4, 5 A, B) descending, distal 0.2 distinctly ascending; exceeding distal margin of third segment of antennular peduncle but not reaching distal margin of antennal scale; 0.6 times carapace length; dorsal margin armed with 7 evenly spaced teeth, including 5 on rostrum proper and 2 postrostral teeth along midline of the carapace; posteriormost tooth arising at 0.1 CL; ventral margin with blade becoming somewhat deeper distally, with 5 evenly spaced teeth in distal 0.4.

Carapace (Figs. 4, 5 A, B) with low median portrostral carina extending 0.5 of carapace; dorsal profile in lateral view slightly convex. Orbital margin concave; suborbital lobe bluntly triangular, not reaching antennal tooth. Antennal tooth moderately strong, acute, exceeding suborbital lobe and pterygostomial tooth. Pterygostomial tooth small. Anterolateral margin between antennal tooth and pterygostomial tooth straight.

Abdomen (Fig. 4) dorsally rounded, posterodorsal margin of third somite produced. Pleura of anterior four somites broadly rounded, unarmed; fifth pleuron armed with posteroventral tooth (Figs. 4, 5 C). Sixth somite approximately 1.4 times longer than fifth, 1.9 times longer than deep, with small posteroventral tooth; posterolateral process terminating in small tooth.

Telson (Figs. 4, 5 D) damaged, incomplete distally. Incomplete length 2.1 times anterior width and as long as sixth abdominal somite in dorsal midline; lateral margins parallel in anterior third, tapering posteriorly, bearing 3 dorsolateral spines on each side; shape and armature of posterior margin unknown.

Uropods (Figs. 4, 5 D) with broad rami exceeding distal margin of incomplete telson; exopod with distinct transverse suture, bearing small fixed spine and one moveable spine at distolateral angle; endopod shorter and narrower than exopod; posterolateral projection of protopod triangular with acute tip.

Eyes (Figs. 4, 5 A, B) subpyriform with stalk narrowing proximally; cornea wider than stalk, its maximum width 0.2 times CL, darkly pigmented; ocellus apparently absent.

Antennular peduncles (Figs. 4, 5 A, B) extending to distal 0.7 of antennal scale, not reaching base of dorsolateral tooth of antennal scale. First segment distinctly longer than distal two segments combined, reaching 0.4 of antennal scale, ventromesial margin armed with strong subdistal tooth; stylocerite exceeding beyond distal margin of first segment of antennular peduncle but not reaching distal margin of second segment, terminating in acute point, mesial margin sinuous. Second segment less than half length of first, with promiment distolateral tooth. Third segment approximately 0.5 length of second, with small dorsodistal tooth. Flagellae damaged, detached from peduncles.

Antenna (Figs. 4, 5 E) with bascicerite bearing small, acute ventrolateral tooth; carpocerite reaching to distal 0.6 of antennal scale. Antennal scale approximately 0.7 times CL, 2.9 times longer than wide; lateral margin straight; distolateral tooth falling short of rounded distal lamella of blade.

Mouthparts similar to those of other species of the genus, without specific characters. Third maxilliped (Fig. 6 A–C) broken, reach unknown. Antepenultimate segment somewhat flattened proximally, approximately 0.9 times as long as two distal segments combined; dorsodistal and distolateral margins armed with a small tooth; small spine at ventrodistal angle (Fig. 6 C); lateral surface with row of spiniform setae on blunt ridge parallel to dorsal margin; exopod reaches midlength. Ultimate segment approximately 3.5 times longer than penultimate segment, with dense tufts of setae; tapering distally, bearing short row of corneous spines distolaterally and distomesially (Fig. 6 B).

Strap-like, terminally hooked epipods present on third maxilliped to third pereopod; corresponding setobranchs on first to fourth pereopods (Fig. 5 F).

First pereopod (Fig. 6 D–E) broken, reach unknown. Chela approximately twice as long as carpus; dactylus approximately 0.6 times as long as palm, weakly curved distally, terminating in two corneous claws; fixed finger terminating in one.

Second pereopod (Fig. 6 F–G) broken, reach unknown, distinctly more slender than first. Chela small with subcylindrical palm; dactlyus terminating in two corneous claws; fixed finger terminating in one. Carpus composed of seven articles.

Third pereopod (Fig. 6 H) incomplete, reach unknown, slender. Dactylus, propodus, and carpus missing; merus armed with one lateral spine.

Fourth pereopod (Fig. 6 I) incomplete, reach unknown, slender. Dactylus, propodus, and carpus missing; merus unarmed.

Fifth pereopod missing.

Colouration in life. Unknown.

Distribution and habitat. Known only from the type locality, the Coral Seamount, southwest Indian Ocean, in 732 m water depth. Collected from the netting of a whale-bone mooring with Lebbeus ketophilos sp. nov.

Etymology. The species name, oreios, is the Greek for “of the mountains”, in reference to the type locality of the new species.

Remarks. Eualus oreios sp. nov. is characterised by the presence of epipods on the anterior three pairs of pereopods and long rostrum exceeding the antennular peduncles. It is therefore most similar to E. kinzeri Tiefenbacher, 1990 and E. leptognathus (Stimpson, 1860). Although the holotype of the new species is incomplete, it is distinguished easily from these species (see below).

Eualus oreios sp. nov. is morphologically closest to E. kinzeri, described from the Weddell Sea in 673–771 m water depth. The new species differs from E. kinzeri in the armature and curvature of the rostrum (5 versus 6–9 ventral teeth; regularly versus irregularly spaced dorsal teeth; descending, distal 0.2 distinctly ascending versus directed straight forward or curving very slightly dorsad), and more slender ventral blade. It is differentiated further from E. kinzeri by the proportions and armature of the antennular peduncles (first segment distinctly longer than distal two segments combined versus just a little longer; third segment half length of second versus equal in size; 1 dorsodistal spine versus 2 dorsolateral spines on third segment) and the proportions of the antennal scale (length 2.9 versus 2.5 times width) and third maxilliped (ultimate segment 3.5 versus 4 times length of penultimate segment). In addition, the merus of the fourth pereopod is unarmed in Eualus oreios sp. nov. (versus bearing 1 spine in E. kinzeri).

The new species is distinguished from Eualus leptognathus by the shape, length, and armature of the rostrum (0.6 versus>0.9 times CL; 7 evenly spaced dorsal teeth versus 3–5 and unarmed distally; 5 versus 2–4 ventral teeth) and straight (versus sinuous) (see Kim et al. 2006: Fig. 3 A) anterolateral margin of the carapace. It is separated further by the reach and armature of the antennular peduncles (reaching distal 0.7 antennal scale versus slightly overreaching midlength; first segment unarmed dorsally versus bearing tooth) and armature of meri of the third and fourth pereopods (1 and 0 spines respectively versus 2–7).