Lebbeus laurentae Wicksten 2010

Lebbeus laurentae Wicksten, 2010

(Figs 1–4, 18)

Lebbeus carinatus de Saint Laurent, 1984: 356; de Saint Laurent 1997: 197, unnumbered fig.; Martin and Haney 2005: 470; Komai 2006: 431, figs. 1–3. Not Lebbeus carinatus Zarenkov, 1976.

Lebbeus laurentae Wicksten, 2010: 196, figs. 1–4.

Material examined. Syntypes: BIOCYARISE, DS Cyana, site Parigo/Pogosud, 12°49’N, 103°57’W, 2630 m, 2 females (cl 13.5, 19.4 mm), 1 male (cl 12.0 mm), 6–30 March 1984, MNHN-Na 14973.

HOT 96 (RV L’Atalante /DS Nautile), dive #1063, EPR 13°N, site Genesis, 12°50'N, 103.54'W, 2640 m, 15 February 1996, slurp gun, 2 males (cl 9.9, 11.4 mm), 1 juvenile (cl 5.6 mm), MNHN-IU-2011-5721. HOPE 99 (RV L’Atalante /DS Nautile), dive #1361, EPR 13°N, site Genesis, 12°50'N, 103.54'W, 2640 m, 17 April 1999, slurp gun, 5 females (cl 8.2–14.9 mm), MNHN-IU-2011-5722; dive #1370, same site, 1 May 1999, 1 male (cl 10.1 mm), 6 females (cl 7.8–14.8 mm), 2 juveniles (cl 4.9, 7.4 mm), MNHN-IU.2011-5723; same dive, 1 male (cl. 11.1 mm), CBM-ZC 10658; dive #1381, same site, 12 May 1999, slurp gun, 1 male (cl 12.8 mm), 1 female (16.2 mm), MNHN-IU-2011-5724; dive #1384, same site, 1 female (damaged), 1 juvenile (cl 7.8 mm), CBM-ZC 10659; dive #1385, same site, 16 May 1999, slurp gun, 2 males (cl 10.0, 12.7 mm), 5 females (cl 8.7–17.1 mm), 1 juvenile (cl 5.9 mm), CBM-ZC 10660; dive #1388, site Elsa, 12°48'N, 103°56'W, 2632 m, 19 May 1999, slurp gun, 3 females (cl 7.8–14.6 mm), 1 juvenile (damaged), MNHN-IU-2011-5725; dive #1389, site Genesis, 20 May 1999, slurp gun, 2 females (cl 13.0, 14.3 mm), MNHN-IU-2011-5726. PHARE, dive #164-16, EPR 13°N, site Actinoir, 12°48.77'N, 103°56.50'W, 2618 m, 25 May 1999, baited trap, 1 female (cl 14.6 mm), 1 male (cl 10.0 mm), MNHN-IU-2011- 5727.

Redescription. Females. Body (Fig. 1) moderately stout for genus; integument soft, surface glabrous.

Rostrum (Fig. 2 A, B) straight, directed forward, reaching to or slightly overreaching distal margin of first segment of antennular peduncle, 0.3–0.5 times carapace length; dorsal margin armed with 2–6 small teeth, including 1–4 teeth on rostrum proper and 1–3 postrostral teeth; ventral margin armed with 1–3 tiny teeth in distal 0.2, ventral lamina poorly developed. Carapace (Figs 1, 2 A, B) with low but distinct postrostral carina extending at least to midlength (usually to two-thirds) of carapace, sloping toward rostral base; posteriormost postrostral tooth arising at 0.1–0.2 of carapace length; dorsal margin in lateral view convex; supraorbital tooth moderately strong, arising at level of rostral base, not reaching tip of suborbital lobe or antennal tooth; orbital region depressed, orbital margin with convexity, base of eyestalk set between this convexity and suborbital lobe; distinct distinct U-shaped notch present inferior to base of supraorbital tooth; suborbital lobe well developed, triangular, reaching tip of antennal tooth; anterolateral margin between antennal and pterygostomial teeth strongly sinuous, with deep excavation below antennal tooth.

Abdomen (Fig. 1) dorsally rounded. Second somite with deep transverse groove on tergum, posteriorly forming low but distinct ridge. Pleura of anterior three somites broadly rounded; fourth pleuron usually with small posteroventral tooth; fifth pleuron with moderately strong posteroventral tooth. Sixth somite about 1.4 times longer than fifth somite and 1.8 times longer than deep, bearing small posteroventral tooth; posterolateral process terminating in small sharp tooth. Telson (Fig. 2 C) 1.5–1.6 times longer than sixth somite, tapering posteriorly to convex posterior margin, bearing 3–7 (usually 4–6) dorsolateral spines on each side; posterior margin with 2 pairs of lateral spines (mesial pair longer) and 5 or 6 median spiniform setulose setae (Fig. 2 D).

Eye (Fig. 2 A, B) very small for genus, subpyriform with stalk slightly narrowing proximally; cornea not dilated, its maximum diameter less than 0.1 of carapace length; ocellus absent.

Antennular peduncle (Fig. 2 A, B) not reaching base of distolateral tooth of antennal scale. First segment much longer than distal two segments combined, slightly overreaching midlength of antennal scale, dorsodistal margin armed with 2–4 slender teeth; stylocerite far falling short of distal margin of first peduncular segment, sharply pointed, mesial margin sinuous. Second segment 0.4–0.5 length of first segment, with l moderately large dorsolateral distal tooth. Third segment less than half as long as second segment, bearing 1 small dorsodistal tooth. Lateral flagellum with thickened aesthetasc-bearing portion about 0.4 times as long as carapace.

Antenna (Fig. 2 A, B, E) with basicerite bearing relatively small ventrolateral tooth; carpocerite reaching distal 0.2–0.3 of antennal scale. Antennal scale about 0.6 times as long as carapace and 2.8–3.0 times longer than wide; lateral margin nearly straight or very slightly concave; distolateral tooth not reaching rounded distal margin of lamella.

Mouthparts similar to those of other species of the genus. Third maxilliped (Fig. 3 A) overreaching antennal scale by half length of ultimate segment; ultimate segment 3.0–3.5 times longer than penultimate segment, tapering distally, with short row of darkly pigmented corneous spines distomesially (Fig. 3 B); antepenultimate segment shorter than distal two segments combined, armed with 1 small tooth on distolateral margin and 1 minute spine at ventrolateral distal angle (Fig. 3 C); lateral surface with row of minute spiniform setae on blunt dorsolateral ridge.

Strap-like, terminally hooked epipods present on third maxilliped to second pereopod, corresponding setobranchs present on first to third pereopod (Fig. 2 F).

First pereopod (Fig. 3 D) moderately stout, reaching distal margin of antennal scale; dactylus about 0.6 times as long as palm, terminating in 2 darkly pigmented corneous claws; fixed finger terminating in single corneous claw (Fig. 3 E). Second pereopod (Fig. 3 F) overreaching antennal scale by 0.7–0.8 length of carpus; carpus divided into 7 articles. Third to fifth pereopods relatively long and slender, similar and slightly decreasing in length posteriorly. Third pereopod (Fig. 3 G) overreaching antennal scale by 0.3 length of carpus; dactylus (Fig. 3 H) 0.14-0.16 times as long as propodus, moderately stout (about 3.0 times longer than deep), terminating in acute, darkly pigmented unguis, armed with 4 darkly pigmented accessory spinules on flexor margin, distalmost accessory spinule subterminal, distinctly larger than others, making tip of dactylus appearing biunguiculate; carpus about 0.6 times as long as propodus; merus armed with 3–7 ventrolateral spines (ventrolateral distal spine usually absent). Fourth pereopod (Fig. 3 I) overreaching antennal scale by full length of propodus; merus with 1–4 (usually 2 or 3) ventrolateral spines. Fifth pereopod (Fig. 3 J) overreaching distal margin of antennal scale by 0.5–0.7 length of propodus; merus usually unarmed, but rarely with 1 lateral spine.

Males. Generally similar to females except for sexually dimorphic characters. Antennular peduncle (Fig. 4 A) reaching distal margin of antennal scale; flagella thicker, outer flagellum slightly longer than carapace, aesthetascbearing portion occupying about half-length of entire flagellum, about half-length of carapace; inner flagellum distinctly longer than outer flagellum, about 1.2–2.0 times longer than carapace. Endopod of first pleopod with minute lobe just lateral to base of terminally located appendix interna (Fig. 4 B). Second pleopod with appendix masculina relatively stout, about half-length of appendix interna, bearing about 15 stiff setae terminally (Fig. 4 C).

Coloration in life. Carapace reddish, rostrum translucent; abdomen translucent. Cornea light gray. Antennae and pereopods translucent.

Distribution. Known only from hydrothermal vents on EPR 13°N; at depths of 2618–2640 m.

Ecology. Lebbeus laurentae was seen in several active vent sites (Parigo, Elsa, Genesis, and Actinoir) which were composed of black smokers (maximum fluid temperature 360°C) surrounded by fluid emission at 5–12°C temperature. Video recordings show that shrimps live among clusters of giant tube worms Riftia pachyptila Jones, 1981. Associated fauna includes the zoarcid fish Thermarces cerberus Rosenblatt & Cohen, 1986, the bythograeid crab Bythograea thermydron Williams, 1980 and the cephalopod Vulcanoctopus hydrothermalis González, Guerra, Pascual & Briand, 1998 (González et al. 1998). Lebbeus laurentae was not seen in clusters of Pompei worms Alvinella pompejana Desbruyères & Laubier, 1980, where the temperature generally exceeds 15°C, and it is suggested that this species prefers lower temperature of less than 15°C. Individuals were sometimes seen at some meters away from the bases of active chimneys, composed of basaltic substrate, together with serpulid worms, and a squat lobster Munidopsis recta Baba, 2005. The density of the shrimps is estimated at 1–3 individuals /m ² in the clusters of Riftia pachyptila. The diet of some individuals was composed of unidentified organic matter (M. Segonzac, unpublished data).

Remarks. Intrageneric grouping within Lebbeus according to the number of pereopodal epipods was first discussed by Rathbun (1904) and has been followed by many authors (e.g., Holthuis 1947; Butler 1980; Wicksten 1990; Hayashi 1992; Komai et al. 2004; Chang et al. 2010). Although phylogenetic significance of the division remains unclear, the number of pereopodal epipods remains useful for discrimination of species in this morphologically disparate and species-rich genus. Lebbeus laurentae belongs to the species group characterized by the presence of epipods on the first and second pereopods. This group contains 17 known species (Komai et al. 2004; Jensen 2006; Chang et al. 2010). Within this group, L. laurentae is unique in the presence of a deep notch inferior to the base of the supraorbital tooth and the substantially reduced eye (the width of the cornea is less than 0.1 times of the carapace length). It is rather similar to the following 13 species, all placed in a group characterized by the presence of epipods on the first to third pereopods: L. antarcticus Hale, 1941, L. carinatus Zarenkov, 1976, L. cristatus Ahyong, 2010, L. formosus Chang, Komai & Chan, 2010, L. kuboi Hayashi, 1992, L. microceros (Krøyer, 1841), L. pacmanus sp. nov., L. polyacanthus Komai, Hayashi & Kohtsuka, 2004, L. shinkaiae sp. nov., L. similior Komai & Komatsu, 2009, L. thermophilus sp. nov., L. washingtonianus, and L. wera. Shared characters are: rostrum falling short of distal margin of first segment of antennular peduncle, bearing more than three dorsal and one or more ventral teeth; deep notch present inferior to base of supraorbital tooth; anterolateral margin of carapace between antennal and pterygostomial teeth strongly sinuous with deep concavity just below antennal tooth; and first segment of antennular peduncle armed with more than one teeth on dorsodistal margin. Other than the absence of an epipod on the third pereopod, the lack of a ventral lamina on the rostrum and the substantially reduced eyes distinguishes L. laurentae from the other 13 species.

This species had long been known as Lebbeus carinatus, although some workers (e.g., de Saint Laurent 1997; Komai et al. 2004; Martin & Haney 2005) pointed out that this name was a junior homonym of Zarenkov’s (1976) L. carinatus. Komai’s (2006) account of this species was erroneously attributed to Zarenkov (1976), although this error was corrected in the corrigendum. Wicksten (2010) finally proposed a new replacement name L. laurentae. Because of the lack of some diagnostic details in the redescription and inaccuracies in the figures given by Wicksten (2010), we here present a detailed redescription and drawings to better understand the morphology of this species.