Lebbeus cristatus Ahyong 2010, sp. nov.

Lebbeus cristatus sp. nov.

(Figs. 1–3A)

Material examined. HOLOTYPE: NIWA 33142, damaged female (tcl 12.7 mm, cl 9.0 mm), 36°54.76’S, 167°32.10’E, Challenger Plateau, New Zealand, 1231– 1226 m, epibenthic sled, with sponges and scleractinian coral (Fungiacyathus fragilis Sars), TAN0707/50, 30.V.2007.

Diagnosis. Rostrum straight, directed anteroventrally, overreaching eye but not reaching distal margin of antennular peduncle article 1; dorsal margin with 2 sharp teeth on rostrum proper and 2 postorbital teeth, posteriormost tooth arising at anterior quarter of carapace; with 2 ventral distal teeth. Antennal scale 3 times as long as wide; distolateral tooth almost reaching to distal margin of blade. Postrostral median ridge distinct, slender, extending slightly beyond posterior three-fourths of carapace. U-shaped notch ventral to base of supraorbital spine. Abdominal somite 2 with shallow transverse dorsal groove, posteriorly forming low ridge; pleura 1–4 broadly rounded, unarmed; pleuron 5 with posterolateral spine. Telson with 4 pairs of articulated dorsolateral spines; posterior margin convex, with 2 pairs of articulated posterolateral spines and 7 mesial spinules. Antennular peduncle reaching to distal 0.8 of scaphocerite; article 1 with 3 distolateral spines; stylocerite reaching to base of article 2. Pereopods 1–3 with strap-like epipod.

Description of holotype. Body robust, glabrous. Rostrum straight (Fig. 1C), 0.4 times cl, directed anteroventrally, reaching beyond midlength but not to distal margin of antennular peduncle article 1, laterally compressed, tapering to acute apex; dorsal margin with 4 sharp, widely spaced teeth (2 widely spaced teeth on rostrum proper; 2 postorbital); posteriormost tooth arising from anterior quarter of carapace; ventral margin with 2 equal teeth distally; lateral carina weak, extending from base of supraorbital spine to proximal half of rostrum. Postrostral median ridge (Fig. 1A, B) pronounced, slender, extending slightly beyond posterior threefourths of cl.; general dorsal profile broadly convex. Supraorbital spine strong; U-shaped notch ventral to base of supraorbital spine (Fig. 1C). Anterolateral margin between supraorbital notch and suborbital lobe convex. Suborbital lobe narrowly, slender, apex rounded (Fig. 1D). Antennal spine slender, not overreaching suborbital lobe, without carina. Pterygostomial spine small, slender, not reaching midlength of antennal spine (Fig. 1C). Anterolateral margin between antennal spine and pterygostomial spine convex.

Abdomen rounded dorsally; somite 2 with shallow transverse dorsal groove, posteriorly forming low ridge; somite 3 posterodorsal margin produced; pleura 1–4 broadly rounded, unarmed; pleuron 5 with posterolateral spine (Fig. 1A). Abdominal somite 6 length 1.4 times that of somite 5, 2.0 times height; with blunt posteroventral angle and strong, triangular posterolateral tooth.

Telson (Fig. 1G) length 2.9 times anterior width, 5.8 times posterior width, 1.6 times length of somite 6; margins parallel in anterior third, and tapering posteriorly to convex posterior margin; with 4 pairs of dorsolateral spines; with 2 pairs of posterolateral spines (inner longer), 7 setose mesial spinules and several fine setae.

Thoracic and abdominal sternites unarmed.

Eye subglobular, cornea wider than stalk; ocellus absent; maximum corneal diameter 0.2 times cl (Fig. 1A, D).

Antennular peduncle (Fig. 1D) reaching to distal 0.8 of antennal scale. Article 1 longer than articles 2 and 3 combined; reaching almost to midlength of antennal scale; with 3 distolateral dorsal spines and 1 subdistal ventrolateral spine (Fig. 1E); stylocerite sharp, reaching base of article 2. Article 2 about half as long as article 1; 2.2 times longer than wide; with stout distolateral spine. Article 3 about half as long as article 2; with conical distodorsal spine. Lateral flagellum with thickened aesthetasc-bearing portion 0.4 cl.

Antennal scaphocerite (Fig. 1F) 0.6 times cl, 3.0 times as long as wide; lateral margin faintly concave; distolateral tooth directed anteriorly, almost reaching to broadly rounded distal margin of blade. Basicerite with slender ventrolateral spine. Ultimate peduncle article length 4 times width.

Mouthparts not dissected; mandibular palp 2-articulate.

Maxilliped 3 (Fig. 2A) with 4 articles; exceeding antennal scale by about two-thirds length of ultimate article (= dactylus + propodus). Ultimate article about 3.5 times length of penultimate article (= carpus); with transverse tufts of setae; distodorsally with two rows of 5 or 6 corneous spinules; antepenultimate article (= fused merus, ischium and basis) flattened dorsoventrally, marginally setose; 1 distolateral spine; 1 small distal, articulated, ventrolateral spine. epipod strap-like, distally hooked.

Pereopod 1 (Fig. 2B, C) moderately stout, reaching to about apex of antennal scale. Chela about 1.65 times longer than carpus. Dactylus about 0.6 times as long as palm, strongly curved distally, terminating in 2 parallel corneous claws; occlusal margin entire. Pollex terminating in single corneous claw; occlusal margin entire. Palm subcylindrical. Carpus 2.5 times as long as distal width. Merus subcylindrical, obliquely articulated with ischium; 1.7 times longer than carpus and 4.5 times greatest width; surfaces sparsely setose. Epipod strap-like, distally hooked; setobranch present.

Pereopod 2 slender (Fig. 2D), overreaching antennal scale by half length of chela and carpus combined. Chela small; palm subcylindrical; dactylus 0.7 times as long as palm, with 2 blunt terminal claws. Pollex with 1 terminal claw. Occlusal margins of fingers entire. Carpus 3.9 times longer than chela, 7-articulate, in following ratios from proximal end:

1.0: 0.8: 1.6: 1.0: 0.7: 0.5: 0.9. Merus 0.6 times as long as carpus. Ischium 1.1 times longer than merus. Epipod strap-like, distally hooked; setobranch present.

Pereopods 3–5 long and slender, similar in structure, decreasing slightly in length posteriorly; sparsely setose.

Pereopod 3 (Fig. 2F) overreaching antennal scale by length of propodus; dactylus slender, corneous, bispinous unguis and with single row of 5–7 slender, articulated, corneous spines on flexor margin; propodus 14.3 times longer than high, with 2 rows of flexor spinules; carpus 0.6 times as long as propodus, unarmed; merus 9.6 times longer than deep, with 2 or 3 articulated lateral spines; ischium 0.5 length of merus, unarmed; epipod strap-like, distally hooked; setobranch present.

Pereopod 4 (Fig. 2G) dactylus slender, corneous, bispinous unguis and with single row of 5 or 6 slender, articulated, corneous spines on flexor margin; propodus with 2 rows of flexor spinules; merus with 1 articulated lateral spine distally. Epipod absent; setobranch present.

Pereopod 5 (Fig. 2H) dactylus slender, corneous, bispinous unguis and with single row of 6 slender, articulated, corneous spines on flexor margin; propodus with 2 rows of flexor spinules; merus with 1 articulated lateral spine distally. Epipod absent; setobranch absent.

Uropodal protopod acutely produced posteroventrally; rami subequal in length, extending posteriorly slightly beyond telson apex when folded; endopod length 3 times width; exopod with small articulated spine mesial to smaller distolateral tooth; diaeresis sinuous (Fig. 1G).

Colour in life. (Fig. 3A) Carapace bright red anteriorly; posterior upper quarter and lateral half clear/pale. Abdomen pale, with diffuse, scattered red chromatophores. Antennular and antennal flagella colourless. Maxilliped 3 red. Pereopod 1 red with pale palm. Pereopods 2–5 deep red on proximal half, becoming diffuse to transparent on distal half.

Etymology. Named cristatus (Latin) for the long dorsal carina on the carapace.

Remarks. Lebbeus cristatus sp. nov. belongs to the group of species within the genus sharing the presence of an epipod on pereopods 1–3, a distinct U-shaped notch below the supraorbital spine; dorsal and ventral rostral spines, and a short rostrum that reaches beyond the eye but not beyond the antennular peduncle article 1 (at least in females). Of these species only two lack an unarmed pleuron on abdominal somite 4 as in L. cristatus: L. antarcticus (Hale, 1941) from Antarctica and possibly L. profundus (Rathbun, 1906) from Hawaii (presence of U- or V-shaped notch below the supraorbital spine not known). The new species can be distinguished from L. antarcticus by the longer stylocerite, which reaches to the base of antennular peduncle article 2, rather than to not more than the distal three-fourths of article 1; and a rounded rather than triangular posterior margin of the telson. From L. profundus, L. cristatus is readily distinguished by the presence of 2 instead of no postorbital spines, and shorter third maxillipeds in which the distal article overreaches the scaphocerite by about two-thirds the distal article length rather than its entire length. In many respects, L. cristatus most closely resembles L. kuboi Hayashi, 1992 from Japan, particularly in the long postrostral carina on the carapace, robust body form and similar proportions and ornamentation of the antennular peduncle. Lebbeus cristatus, however, is readily distinguished from L. kuboi by the shorter rostrum (not-reaching versus overreaching the first antennular article), a proportionally wider scaphocerite (3.0 times versus 3.3–3.8 times longer than wide); an unarmed posterolateral margin of pleuron 4; and fewer spines on the meri of pereopods 3–4 (2 or 3 on pereopod 3 and 1 on pereopod 4 versus 5–9 on pereopod 3 and 4–10 on pereopod 4). The prominence of the dorsal postrostral carina is sexually dimorphic in L. kuboi, being slightly shorter and lower in males than mature females (Komai et al. 2004). Thus, similar dimorphism can probably be expected when males of L. cristatus are found.

Lebbeus cristatus is the second known species of the genus from New Zealand. The only other known Lebbeus from the region, L. wera Ahyong, 2009 (Fig. 3B), occurs on hydrothermal vents on the southern Kermadec Ridge; it is readily separated from L. cristatus by the presence of 5 instead of 2 postorbital spines on the carapace, 4 instead of 6 or 7 pairs of dorsal telson spines, and colouration — more uniform red-orange in L. wera, versus red anteriorly and pale posteriorly in L. cristatus.

Distribution. Presently known only from the type locality, Challenger Plateau, at 1226–1231 m.