Lebbeus ketophilos , Nye, Verity, 2013
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Lebbeus ketophilos sp. nov.
Material examined. Holotype: male, CL 6.8 mm. Coral Seamount, southwest Indian Ocean; co-ordinates: 41 ° 22.38 S 42 ° 54.64 E; water depth: 732 m [OUMNH.ZC. 2013 -01-002]. Collected on the 66 th voyage of RRS ‘James Cook’, November 2011.
Description. Body moderately robust for genus; integument glabrous, moderately firm.
Rostrum ( Figs. 1View FIGURE 1, 2View FIGURE 2 A –B) long and slender, anterior part curved distinctly upward, 1.0 times CL; reaching to but not exceeding distal margin of antennal scale; laterally compressed, tapering to acute apex; dorsal margin armed with 3 widely spaced postrostral teeth (0 teeth on rostrum proper) along midline of carapace, posteriormost tooth arising at 0.4 CL; ventral margin armed with 5 teeth in distal 0.6, ventral lamina poorly developed.
Carapace ( Fig. 1View FIGURE 1) with low but distinct median portrostral carina extending to posterior two-thirds of carapace; dorsal profile in lateral view gently convex; supraorbital tooth strong, arising level with posterior margin of orbit, directed forward, not reaching tip of antennal tooth; deep V-shaped notch inferior to base of supraorbital tooth; orbital margin weakly concave; suborbital lobe well developed, bluntly triangular; antennal tooth well-developed, acute, exceeding tip of suborbital lobe. Pterygostomial tooth small, not reaching antennal tooth. Anterolateral margin between antennal tooth and pterygostomial tooth strongly sinuous with deep excavation below antennal tooth.
Abdomen ( Fig. 1View FIGURE 1) rounded dorsally. Second somite with transverse groove on tergum, bordered posteriorly by low ridge; posterodorsal margin of third somite produced; pleura of anterior three somites unarmed marginally, posteroventral margin rounded; fourth pleuron with posteroventral tooth ( Fig. 2View FIGURE 2 C); fifth pleuron bearing moderately strong posteroventral tooth ( Fig. 2View FIGURE 2 C). Sixth somite 1.5 times longer than fifth; armed with small posteroventral tooth; posterolateral process terminating in acute tooth.
Telson ( Figs. 1View FIGURE 1, 2View FIGURE 2 D –E) length 3.0 times anterior width, 1.3 times longer than sixth abdominal somite in dorsal midline; lateral margins tapering to convex posterior margin, bearing 6 / 5 (left/right) dorsolateral spines; posterior margin with 2 pairs of lateral spines (mesial pair longer) and 2 median spiniform setulose setae.
Antennular peduncles ( Fig. 1View FIGURE 1, 2View FIGURE 2 A –B) extending approximately to distal 0.2 of antennal scale. First segment as long as distal two segments combined, not quite reaching midlength of antennal scale, dorsodistal margin armed with 2 slender teeth, ventromesial margin armed with 1 prominent subdistal tooth; stylocerite slightly exceeding dorsodistal margin of first peduncular segment, terminating in acute point, mesial margin sinuous. Second segment approximately 0.5 length of first segment; bearing strong distolateral tooth. Third segment less than half as long as second; with small dorsodistal tooth. Lateral flagellum with thickened aesthetasc-bearing portion approximately 0.4 times CL.
Antenna ( Figs. 1View FIGURE 1, 2View FIGURE 2 H) with bascicerite bearing small, acute ventrolateral tooth; carpocerite reaching to approximately distal 0.6 of antennal scale. Antennal scale 0.8 times CL, 3 times longer than wide; lateral margin straight; distolateral tooth slightly exceeding rounded distal lamella of blade.
Mouthparts similar to those of other species of the genus. Third maxilliped ( Fig. 3View FIGURE 3) exceeding antennal scale by approximately 0.2 length of ultimate segment. Antepenultimate segment approximately 0.8 times as long as 2 distal segments combined; bearing a small tooth and long spiniform seta on distolateral margin and a small spine at ventrodistal angle ( Fig. 3View FIGURE 3 B); lateral surface bearing row of spiniform setae on blunt ridge parallel to dorsal margin. Ultimate segment approximately 3 times longer than penultimate segment, with dense tufts of setae; tapering distally, with short row of corneous spines distomesially and distolaterally ( Fig. 3View FIGURE 3 C).
Strap-like, terminally hooked epipods present on third maxilliped to third pereopod ( Figs. 3View FIGURE 3 A, D, F, H); corresponding setobranchs on first to fourth pereopods ( Figs. 3View FIGURE 3 D, F, H, I).
First pereopod ( Fig. 3View FIGURE 3 D) moderately stout, extending to distal margin of antennal scale. Chela ( Fig. 3View FIGURE 3 E) approximately 1.4 as long as carpus; dactylus approximately 0.6 times as long as palm, strongly curved distally, terminating in 2 corneous claws; fixed finger terminating in 1 corneous claw.
Second pereopod ( Fig. 3View FIGURE 3 F) distinctly more slender than first, overreaching antennal scale by approximately 0.2 length of carpus when extended. Chela ( Fig. 3View FIGURE 3 G) small; dactlyus terminating in two corneous claws; fixed finger terminating in one corneous claw. Carpus divided into 7 articles.
Third to fifth pereopods ( Fig. 3View FIGURE 3 H –J) similar in structure, long and slender, decreasing in length and stoutness posteriorly. Third pereopod ( Fig. 3View FIGURE 3 H) overreaching antennal scale by approximately 0.3 length of propodus; dactylus damaged, distal tip missing, armed with 5 accessory spinules on flexor margin; carpus approximately 0.6 length of propodus; propodus with 2 rows of ventral flexor spinules; merus armed with 4 / 5 (left/right) lateral spines.
Fourth pereopod ( Fig. 3View FIGURE 3 I) overreaching antennal scale by approximately 0.2 length of propodus; dactlyus damaged, distal tip missing, armed with 5 accessory spinules on flexor margin; propodus with two rows of ventral flexor spinules; merus armed with 4 / 3 (left/right) lateral spines.
Fifth pereopod ( Fig. 3View FIGURE 3 J) not overreaching antennal scale; dactlyus ( Fig. 3View FIGURE 3 K) 0.15 length of propodus, terminating in acute unguis and armed with 6 accessory spinules on flexor margin, distalmost spinule distinctly larger than others, making dactylus tip appear biunguiculate; propodus with two rows of ventral flexor spinules; merus armed with 1 lateral spine.
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 Eualus oreios sp. nov.
Etymology. The species name, ketophilos , is the combination of the Greek, “ ketos ” (= whale), and “ philos ” (= loving), in reference to its collection from a whale –bone mooring.
Remarks. Lebbeus ketophilos sp. nov. belongs to the group of species within the genus characterised by the presence of epipods on the anterior three pairs of pereopods and absence of armature on the anterior three abdominal pleura. With its long (as long as the carapace), distinctly upturned rostrum, the new species most closely resembles L. indicus Holthuis, 1947 , described and known only from the Bali Sea in 1018 m water depth (Holthuis 1947; Chace 1997; Fransen 1997).
Lebbeus ketophilos sp. nov. is distinguished from L. indicus by the armature of the rostrum (3 dorsal teeth, all postrostral, versus 4 dorsal teeth, including 2 on the rostrum proper; 5 versus 6 ventral teeth) and the third segment of the antennular peduncle (1 versus 2 teeth). The new species is separated further from L. indicu s by the presence (versus absence) of a posteroventral tooth on the fourth abdominal pleuron and the absence (versus presence) of setae on the outer margin of the stylocerite. Furthermore, it is differentiated by the proportionally longer antennal scale (reaching tip of rostrum versus not reaching) with distolateral tooth exceeding (versus not reaching) distal lamella, and the proportionally shorter third maxilliped (exceeding antennal scale by approximately 0.2 versus 0.5 length of ultimate segment). The new species also differs from L. indicus in the armature of the meri of the third and fifth pereopods (4 or 5 versus 6; 1 versus 2 spines).
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