Lebbeus quadratus Chan & Komai, 2017, n. sp.

• Main Authors: Chan, Tin-Yam, Komai, Tomoyuki
• Format: Text
• Language: unknown
• Published: Zenodo 2017
• Subjects: Biodiversity; Taxonomy; Animalia; Arthropoda; Malacostraca; Decapoda; Hippolytidae; Lebbeus; Lebbeus quadratus; Baja; Ross Sea; Okhotsk; Pacific; Antarc*; Antarctica; Alaska
• Online Access: https://dx.doi.org/10.5281/zenodo.6017872; https://zenodo.org/record/6017872

Lebbeus quadratus n. sp. Figs. 1–3 Material examined. Taiwan, Four Way Closure Ridge, 22°03.5049’N, 119°48.4369’E – 22°3.9253’N, 119°48.0218’E, 1300–1502 m, baited trap, April 2014, holotype, female cl 13.4 mm (NTOU M02039). Description. Rostrum (Fig. 1 A) broken at tip, slightly descending at base but strongly curving upwards distal to eyes, overreaching scaphocerite, preserved part 1.2 times as long as carapace; deepest at about midlength, about 0.25 of carapace height; dorsal boarder armed with 3 relatively strong teeth near rostral base, including 2 teeth on carapace posterior to orbital margin, posteriormost tooth arising at 0.25 of cl; ventral blade well developed, its border bearing 5 teeth in distal half, slightly more widely spaced distally; lateral carina obsolete. Carapace (Fig. 1 A, B) with low and blunt postrostral ridge extending to near posterior margin; orbital margin evenly concave; supraorbital tooth distinct with base situated just behind orbital margin, lacking notch below; suborbital lobe distinct and rounded (Fig. 1 B); antennal tooth well developed, somewhat elongate; pterygostomial tooth smaller than antennal and supraorbital teeth; anterolateral margin between antennal and pterygostomial teeth gently sinuous. Abdomen (Fig. 1 E) with pleuron V bearing strong posteroventral tooth, unarmed on pleura I–IV; tergite III dorsally rounded but somewhat produced posteriorly; somite VI 1.7 times longer than somite V, with small posterovental tooth and sharply pointed posterolateral process. Telson (Fig. 1 F) 1.4 times longer than abdominal somite VI, armed with 5 pairs of dorsolateral spines; distal margin bluntly triangular, bearing 2 pairs of moderately long lateral teeth (mesial pair longer) and 7 median spinules as well as some long setae. Eyes (Fig. 1 C) subpyriform; corneas strongly dilated and subspherical in shape, darkly pigmented, its diameter about 0.2 times of carapace length; no ocellar spot evident; stalks short. Antennular peduncle (Fig. 1 C) with basal segment longer than distal 2 segments combined; bearing distinct dorsolateral distal spine on each segment, progressively larger posteriorly; stylocerite slender and partially touching basal segment mesially, terminating in elongated sharp tooth, reaching midlength of second segment. Antennal peduncle (Fig. 1 C, D) with stout basicerite bearing slender ventrolateral distal tooth. Scaphocerite 0.8 times as long as carapace and 3.2 times longer than wide, lateral margin very slightly concave, distolateral tooth far falling short of distal margin of lamella. Carpocerite overreaching midlength of scaphocerite. Maxilliped III endopod (Fig. 2 A) overreaching scaphocerite by 0.2 length of ultimate segment; ultimate segment 3.8 times longer than penultimate segment, distal part bearing some black corneous spines partially circumscribing terminal margin (Fig. 2 B); antepenultimate segment subequal in length to distal two segments combined, distal margin bearing 1 dorsal and 1 lateral spiniform teeth as well as 1 ventrolateral spinule (Fig. 2 C). Exopod absent; strap-like epipod with distinct terminal hook present. Pereiopod I (Fig. 1 D) moderately stout, extending to 0.7 of scaphocerite; segments generally unarmed except for a dorsoproximal denticle on merus; chela (Fig. 1 E) 1.3 times longer than carpus; fingers 0.7 times as long as palm, distal part partially obscured by tufts of stiff setae, dactylus terminating into 2 dark corneous claws (mesial one smaller), fixed finger terminating into a single dark corneous claw; epipod strap-like and with distinct terminal hook; setobranch corresponding to epipod on maxilliped 3 absent. Pereiopod II (left one missing, right side with most carpal articles accidentally lost after examination) slender, without epipod; overreaching scaphocerite by chela and distal 2 carpal articles; chela about 0.2 as long as carpus; carpus consisting of 7 articles, proximal third article longest occupying about half of carpal length; setobranch corresponding to epipod on pereiopod 1 absent. Pereiopods III to V lacking epipods and setobranchs, relatively long and slender, generally similar. Pereiopod III (Fig. 2 F) overreaching scaphocerite by 0.8 of propodus; dactylus (Fig. 2 G) 0.15 (left) or 0.17 (right) times as long as propodus, bearing 4 accessory spinules decreasing in size proximally, clearly demarcated unguis and accessory spinules corneous, darkly pigmented; propodus with 2 rows of movable spinules on flexor surface; carpus unarmed; merus armed with 8 (left) or 9 (right) movable spines on lateral surface, distalmost spine largest; ischium unarmed. Pereiopod IV (Fig. 2 H) overreaching scaphocerite by half of propodus; dactylus 0.14 times as long as propodus and also with 4 accessory spinules; merus with 5 (left) or 7 (right) lateral spines. Pereiopod V (Fig. 2 I; right side with distal segments broken off) overreaching scaphocerite by 0.25 of propodus; dactylus 0.15 times as long as propodus, with 4 accessory spinules; distal part of propodus with tufts of dense grooming setae (some even plumose) on flexor surface; merus with 4 lateral spines. Pleopods without distinctive features. Uropod (Fig. 1 F) with exopod slightly longer than endopod, armed with a small posterolateral tooth accompanied with a larger movable spine at diaeresis. Eggs (not eyed) oval, large, with diameters of 1.8 x 2.5 mm. Coloration (Fig. 3). Body generally reddish translucent. Carapace and appendages generally reddish, posterior carapace paler in color and somewhat translucent. Rostrum except for posteriormost dorsal tooth, lateral parts of antennal peduncle and scaphocerite mostly translucent. Eyes black brown. Abdomen mostly translucent with faint broad reddish transverse bands on posterior part of each tergite; tail fan mainly reddish, exopods and endopods of pleopods also reddish. Eggs (not eyed) greenish. Distribution. Only known from the type-locality off southwestern Taiwan, at depths of 1300–1502 m. Etymology. The Latin quadratus , meaning square, alludes to the type-locality of this new species, Four Way Closure Ridge. Remarks. Although sometimes there are intra-specific variations in the presence or absence of epipods on the thoracic appendages ( e.g. , Komai et al. 2004), the genus Lebbeus is divided into four informal species groups according to the number of epipods on maxilliped III through pereiopod III (see Hayashi 1992; Komai et al. 2004). The present new species belongs to the group bearing epipods only on the maxilliped III and the pereiopod I. Seven taxa are currently placed in this group, viz. L. vicinus vicinus (Rathbun, 1902), L. vicinus montereyensis Wicksten & Mèndez, 1982, L. longipes (Kobjakova, 1936), L. curvirostris Zarenkov, 1976, L. elegans Komai, Hayashi & Kohtsuka, 2004, L. manus Komai & Collins, 2009 and L. kiae Schiaparelli, Ahyong & Bowden, 2015. The new species is readily distinguished from L. longipes (Sea of Japan and Sea of Okhotsk) in lacking a posteroventral tooth on the abdominal pleuron IV, and from L. elegans (Sea of Japan), L. vicinus vicinus (Alaska) and L. kiae (Ross Sea) in having only three dorsal rostral teeth (vs. four to eight dorsal rostral teeth; see Rathbun 1904; Komai et al. 2004; Schiaparelli et al. 2015). Lebbeus vicinus motereyensis (Baja California) has three or four dorsal rostral teeth but it has a much shorter rostrum (about 0.7 of carapace length) far falling short of the distal margin of the scaphocerite and fewer ventral rostral teeth (four vs. five in the new species; see Wicksten & Méndez 1982). Lebbeus quadratus n. sp. is closest to L. manus and L. curvirostris. The dactyli of the posterior three pereiopods have four accessory spinules on flexor margins in L. quadratus n. sp. , but five in both L. curvirostris and L. manus (Fransen 1997; Komai & Collins 2009). However, the number of accessory spinules is rather variable in the species of this genus (see Komai et al. 2004; Komai 2015, Matsuzaki et al. 2015) and might be unreliable for differentiating the new species from these two close relatives. The new species, nevertheless, can be distinguished from L. curvirostris and L. manus in having more numerous lateral spines on the meri of pereiopods III and V. In L. quadratus n. sp. , there are eight or nine spines and four spines on pereiopods III and V, respectively. On the other hand, in L. curvirostris there are six spines and one spine (see Fransen 1997); in L. manus , there are five spines and two spines (see Komai & Collins 2009) on pereiopods III and V, respectively. Moreover, the supraorbital tooth on the carapace is relatively large and with the base located just behind the orbital margin in L. quadratus n. sp. (Fig. 1 A, B), instead of rather minute and arising at the level of the orbital margin in L. curvirostris (cf. Fransen 1997: fig. 47) and L. manus (cf. Komai & Collins 2009: fig. 2A). Lebbeus manus further differs from the other two species in the antennular stylocerite less elongate (just overreaching first antennular segment [Komai & Collins 2009: fig. 2B] versus reaching midlength of second antennular segment [Fig. 1 C; Fransen 1997: fig. 48]) and the rostrum less curved (Komai & Collins 2009: fig. 2A). The difference in the rostrum, however, might potentially be attributed to sexual differences, because the holotype of L. manus is a male whereas the holotypes of L. curvirostris and L. quadratus n. sp. are females. As have been shown for the other congeneric species, the rostrum is sometimes less strongly curved and more slender in males than in females in species of Lebbeus (see Matsuzaki et al. 2015; Komai et al. 2016). Species of Lebbeus have large eggs and generally, at least as currently understood, have rather narrow geographical range ( e.g. , Hayashi 1992; Komai et al. 2004, 2012; Jensen 2006; Komai 2015). The geographic distances amongst Taiwan, Papua New Guinea and Peru also support the recognition of the present new species. Unfortunately, the holotype of L. manus has been preserved in formalin, while the few specimens known of L. curvirostris were collected more than 50 years ago in 1968. Hence, molecular genetic comparison amongst these three closely related species has not yet been possible. Although the present new species was obtained from an area where a cold seep is present, it was collected by a deep-water trap. Thus, whether L. quadratus n. sp. truly inhabits a cold seep itself is uncertain. The closely related species L. manus has been collected from a deep-sea hydrothermal vent (1575 m, Komai & Collins 2009), while the habitat of L. curvirostris is unknown except that the specimens originated from a similar depth (1680–1860 m: Zarenkov 1976; Fransen 1997). : Published as part of Chan, Tin-Yam & Komai, Tomoyuki, 2017, A new shrimp species of the genus Lebbeus White, 1847 (Crustacea: Deacpoda: Caridea: Thoridae) from a deep-sea cold seep site off southwestern Taiwan, pp. 426-432 in Zootaxa 4238 (3) on pages 427-431, DOI: 10.11646/zootaxa.4238.3.9, http://zenodo.org/record/345816 : {"references": ["Komai, T., Hayashi, K. & Kohtsuka, H. (2004) Two new species of the shrimp genus Lebbeus White from the Sea of Japan, with redescription of Lebbeus kuboi Hayashi (Decapoda: Caridea: Hippolytidae). Crustacean Research, 33, 103 - 125.", "Hayashi, K. (1992) Studies on the hippolytid Shrimps from Japan-VIII. The genus Lebbeus White. Journal of Shimonoseki University Fisheries, 40, 107 - 138.", "Rathbun, M. J. (1902) Descriptions of new decapod crustaceans from the west coast of North America. Proceedings of the U. S. National Museum, 24, 885 - 905.", "Wicksten, M. K. & Mendez, M. G. (1982) New records and new species of the genus Lebbeus (Caridea: Hippolytidae) in the eastern Pacific Ocean. Bulletin of the Southern California Academy of Sciences, 81, 106 - 120.", "Kobjakova, Z. I. (1936) Zoogeographical review of the decapod fauna from the Okhotsk and Japanese Seas. Trudy Leningradskogo Obchestva Estestvoispitateleii, 65, 187 - 228. [in Russian with English summary]", "Zarenkov, N. A. (1976) On the fauna of decapods of the waters adjacent to South America. Byulleten' Moskovskogo Obshchestva Ispytatelei Prirody, Otdel Biologicheskii, 5, 8 - 18. [in Russian]", "Komai, T. & Collins, P. (2009) Two species of caridean shrimps (Decapoda: Hippolytidae and Nematocarcinidae) newly recorded from hydrothermal vents on the Manus Basin, southwestern Pacific. Crustacean Research, 38, 28 - 41.", "Schiaparelli, S., Ahyong, S. T. & Bowden, D. (2015) Evidence of niche conservatism and host fidelity in the polar shrimp Lebbeus kiae n. sp. (Decapoda: Caridea: Thoridae) from the Ross Sea, Antarctica. Hydrobiologia, 761, 45 - 69. https: // doi. org / 10.1007 / s 10750 - 015 - 2403 - 1", "Rathbun, M. J. (1904) Decapod crustaceans of the northwest coast of North America. Harriman Alaska Expedition, 10, 1 - 190, plates 1 - 10.", "Fransen, C. H. J. M. (1997) Lebbeus africanus spec. nov., a new shrimp (Crustacea, Decapoda, Caridea, Hippolytidae) from Mauritanian waters, with redescriptions of four other species in the genus. Zoologische Mededelingen, 71, 231 - 260.", "Matsuzaki, K., Hibino, M. & Komai, T. (2015) A new species of the caridean shrimp genus Lebbeus White, 1847 (Crustacea: Decapoda: Thoridae) from the southwestern Sea of Okhotsk, Hokkaido, Japan. Zootaxa, 4032 (3), 309 - 318. https: // doi. org / 10.11646 / zootaxa. 4032.3.6", "Komai, T., Tsuchida, S. & Segonzac, M. (2012) Records of species of the hippolytid genus Lebbeus White, 1847 (Crustacea: Decapoda: Caridea) from hydrothermal vents in the Pacific Ocean, with descriptions of three new species. Zootaxa, 3241, 35 - 63.", "Jensen, G. C. (2006) Three new species of Lebbeus (Crustacea: Decapoda: Hippolytidae) from the Northeastern Pacific. Zootaxa, 1383, 23 - 43."]}