Lebbeus parvirostris Komai & Chen, 2024, sp. nov.
Creators: name: Komai, Tomoyuki
name: Chen, Chong
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Thoridae
Lebbeus
Lebbeus parvirostris

description: Lebbeus parvirostris sp. nov.
[New Japanese name: Kyorasan-ibara-mo-ebi]
(Figs. 1–5)
Lebbeus cf. shinkaiae.—Chen et al. 2023: fig. 3M.
Material examined. Holotype. CBM-ZC 17848, female (cl 7.4 mm), preserved in 99% ethanol, Kyorasan site, Amami Rift hydrothermal vent field (28°36.3611’N, 128°44.0891’E; 628 m deep), by suction sampler mounted on HOV Shinkai 6500, R/V Yokosuka cruise YK23-16S, 19 September 2023.
Paratype. CBM-ZC 17849, 1 female (cl 4.6 mm), same preservation and data as holotype.
Description. Holotype female. Body (Fig. 1) robustly built.
Rostrum (Fig. 2A, B) short, 0.26 times as long as carapace, laterally compressed, reaching beyond midlength of first article of antennular peduncle or distal corneal margin of forwardly directed ocular peduncle; dorsal margin sloping down anteriorly, serrated with 5 small equidistant teeth, including 2 postorbital, posteriormost tooth located at 0.1 carapace length; ventral margin slightly concave, armed with 1 small subdistal tooth, blade not developed. Carapace (Figs. 1, 2A, B) glabrous, with low postrostral ridge not reaching midlength; supraorbital spine moderately small, forwardly directed; conspicuous U-shaped notch below base of supraorbital spine; suborbital lobe well developed, triangular with subacute tip, falling slightly short of moderately small antennal spine; anterolateral margin below antennal spine sinuous with deep concavity just below antennal spine and rounded, unarmed pterygostomial margin; lateral face smooth, without ridges.
First to third pleomeres (Fig. 1) with pleura rounded marginally; fourth pleomere pleuron damaged on both sides (Figs. 1, 2C); fifth pleomere pleuron (Fig. 2C) with moderately large posteroventral tooth. Second pleomere tergum (Fig. 1) with shallow transverse groove. Third pleomere tergum (Fig. 1) with moderately produced posterior margin. Sixth pleomere (Fig. 1) 0.5 times as long as carapace, 1.4 times as long as fifth pleomere, 2.1 times as long as proximal height, with small posteroventral tooth; posterolateral process terminating in acute tooth. Telson (Fig. 2D, E) 1.2 times as long as sixth pleomere, 2.6 times as long as wide, with 3 (right) or 4 (left) dorsolateral spiniform setae; lateral margins subparallel in anterior 0.4, tapering thereafter; posterior margin convex, without median tooth, with 2 pairs of unequal spiniform setae and 1 mesial pair of setulose setae.
Eye (Fig. 2A, B) subpyriform; cornea moderately large, wider than stalk, width no more than 0.2 times of carapace length; no ocellar spot.
Antennular peduncle (Fig. 2A, B) reaching distal 0.2 of antennal scaphocerite. First article distinctly longer than distal 2 articles combined, armed with 1 (left) or 2 (right) spines on dorsodistal margin; stylocerite acuminate, reaching distolateral margin of basal article. Second article with 1 small spine at dorsodistal lateral angle. Third article about half-length of second article, with small spine on dorsodistal margin. Outer flagellum with aesthetascbearing portion moderately stout, about half length of carapace; inner flagellum slender, subequal in length to outer flagellum.
Antennal peduncle (Fig. 2A, B, F) with stout basicerite, armed with small ventrolateral distal spine; dorsolateral distal angle produced in blunt lobe. Carpocerite reaching beyond midlength of scaphocerite. Scaphocerite 0.6 times as long as carapace, 2.6 times as long as wide; lateral margin nearly straight, terminating in slender tooth reaching as far as rounded distal margin of lamella.
Mouthparts not dissected.
Strap-like epipods present on third maxilliped and first to third pereopods, corresponding to setobranchs on first to fourth pereopods.
Third maxilliped (Fig. 3A, B) without exopod; endopod overreaching distal end of antennal scaphocerite by about half-length of ultimate article. Antepenultimate article subequal in length to distal 2 articles combined, depressed in proximal part; distolateral margin with slender spiniform seta; lower lateral distal angle also with minute spiniform seta. Ultimate article 2.7 times as long as penultimate article (= carpus), abruptly tapering in distal 0.2, distal part circumscribed by 6 darkly pigmented, robust spiniform setae.
First pereopod (Figs. 3C–E, 4A; only right one preserved) relatively long and stout, overreaching distal end of scaphocerite by half-length of fingers. Basis short, stout. Merus 4.0 times as long as wide, with short row of minute spiniform setae on lower margin proximally and minute spiniform tubercle proximally on dorsolateral surface. Carpus widened distally, with grooming apparatus on flexor surface distally (grooming apparatus consisting of deep concavity partially surrounded by row of stiff setae). Chela 1.6 times as long as carpus, 3.8 times as long as wide; palm 1.1 times as long as carpus, 2.6 times as long as wide, with short row of stiff setae, consisting of grooming apparatus, on mesial face proximally; fingers each with tufts of short setae distally, fixed finger terminating in darkly pigmented, clearly demarcated unguis; dactylus 0.6 times as long as palm, gently curved, terminating in 2 darkly pigmented ungues.
Second pereopods (Fig. 3F, G) slightly unequal with left longer than right, left overreaching distal end of scaphocerite by length of chela. Ischium 1.2 times as long as merus, with 3 closely set robust setae on lower margin proximally. Carpus divided into 7 segments in left, into 9 segments in right. Chela 0.25 times as long as carpus; dactylus 0.6 times as long as palm.
Third pereopod (Figs. 3H, 4B) relatively slender, overreaching distal end of scaphocerite by 0.7 lengths of propodus. Ischium unarmed.Merus with row of 4 well-spaced spiniform setae on distal half of lateral surface adjacent to lower margin. Carpus 0.5 times as long as propodus, unarmed. Propodus with minute spiniform setae, arranged in 2 rows, on flexor margin. Dactylus 0.2 times as long as propodus, 3.5 times as long as wide, biunguiculate, with 6 accessory spiniform setae over entire length of flexor margin.
Fourth pereopod (Figs. 3I, 4C) generally similar to third pereopod, overreaching distal end of scaphocerite by half-length of propodus. Merus with 3 spiniform setae. Dactylus 3.5 times as long as wide, with 6 accessory spiniform setae in addition to subterminal unguis.
Fifth pereopod (Figs. 3J, 4D) generally similar to third and fourth pereopods, reaching distal end of scaphocerite by tip of dactylus. Merus with only 1 spiniform seta subdistally. Propodus with cluster of short stiff setae, consisting of grooming apparatus, in distal 0.2, followed by minute spiniform setae arranged in 2 rows. Dactylus 3.8 times as long as wide, with 6 accessory spiniform setae in addition to subterminal unguis.
Pleopods without distinguishing features, not illustrated.
Uropodal rami (Fig. 2D) slightly exceeding telson posterior margin. Protopod posterolateral angle produced into strong tooth. Exopod lateral margin terminating in small tooth, accompanied by spiniform seta longer than posterolateral tooth.
Paratype female. Generally similar to holotype, although much smaller. Rostrum with 4 teeth on dorsal margin, including 2 postrostral teeth. Fourth pleuron armed with small posteroventral tooth. Telson with 3 pairs of dorsolateral spiniform setae; posterior margin with 2 pairs of spiniform setae and 2 mesial pairs of plumose setae. Second pereopod carpus divided into 7 segments on both sides. Meri of third to fifth pereopod armed with 3–4, 1, 1 spiniform setae, respectively; dactyli with 6, 6, 6–7 accessory spiniform setae, respectively.
Colouration in life. Body and appendages orange-red overall; cornea brown (Fig. 5).
Distribution. Presently known only from the Amami Rift at a depth of 628 m.
Etymology. From the combination of the Latin “ parvus ” (= small, short) and “ rostris ” (= front), in reference to the short rostrum in the new species. Used as a noun in apposition.
Remarks. Practically, Lebbeus has been subdivided into four informal species groups according to the development of epipods on the first to third pereopods (e.g., Rathbun 1904; Holthuis 1947; Butler 1980; Wicksten 1990; Hayashi 1992; Komai et al. 2004; Komai & Matsuzaki 2022), although the grouping does not always reflect the true phylogenetic relationship (e.g., Komai et al. 2019, 2021; Wang et al. 2023). Lebbeus parvirostris sp. nov. belongs to the group with epipods on the first to third pereopods, and is morphologically similar to species exhibiting the following characteristics: rostrum short, not reaching level of distal end of first article of antennular peduncle, dorsally armed with one or more teeth (in addition to one or two postrostral ones) and ventrally armed with one subterminal tooth; distinct notch present just below supraorbital tooth; first article of antennular peduncle can have more than one spine on dorsodistal margin; meri of third and fourth pereopods with spiniform setae. The species morphologically similar to L. parvirostris sp. nov. include L. microceros (Krøyer, 1841), L. mundus Jensen, 2006, L. saldanhae (Barnard, 1947), L. schrencki (Bražnikov, 1907), L. spongiaris Komai, 2001, and L. tosaensis Hanamura & Abe, 2003.
Lebbeus parvirostris sp. nov. differs from all of these species in the absence of a pterygostomial tooth on the carapace in the female (Fig. 2A). In all of these species the pterygostomial tooth is present in the female, although it may be absent in the male depending on the species (Bražnikov 1907; Squires 1990; Fransen 1997; Komai 2001; Hanamura & Abe 2003; Komai & Takeda 2004; Jensen 2006). Further differences between the new species and these species are discussed below:
Lebbeus microceros. The main differences are seen in the following specific characters: the rostrum overreaches the distal corneal margin in L. microceros (cf. Squires 1990: fig. 112b), rather than not reaching it in L. parvirostris sp. nov. (Fig. 2A, B); the antennular stylocerite reaches or overreaches the level of the dorsodistal margin of the second article of the antennular peduncle in L. microceros (cf. Leim 1921: pl.3, fig. 8, as Spirontocaris zebra; Squires 1990: 112 c) while in L. parvirostris it reaches only to the level of the dorsodistal margin of the first article of the antennular peduncle (Fig. 2C); the antepenultimate article of the third maxilliped is armed with a strong fixed spine at the dorsolateral distal angle in L. microceros (cf. Squires 1990: fig. 113k), whereas such a strong spine is absent in L. parvirostris sp. nov. (Fig. 3A). The colouration of the live animal is also greatly different between the two species. Leim (1921: 138, as Spirontocaris zebra) described the living colour of L. microceros as “spotted over a whitish ground, the spots being a very deep bright red.” As shown in Fig. 5, the body and appendages of L. parvirostris sp. nov. is uniformly orange in general. Lebbeus microceros has been recorded with certainty from the North Atlantic, ranging from Foxe Basin and Southern Greenland to Newfoundland, Nova Scotia and New Brunswick, at depths of 8–80 m (Squires 1990).
Lebbeus mundus. The presence of a deep transverse groove on the second pleomere tergite immediately distinguishes L. mundus from L. parvirostris sp. nov. (Jensen 2006: fig. 5 versus Fig. 1). Furthermore, the supraorbital spine arises distinctly anterior to the rostral base in L. mundus (cf. Jensen 2006: fig. 6A), rather than slightly posterior to the rostral base in L. parvirostris sp. nov. (Fig. 2A); the stylocerite exceeds as far as the dorsodistal margin of the second article of the antennular peduncle in L. mundus (cf. Jensen 2006: fig. 6B), while reaching only as far as the dorsodistal margin of the first article in L. parvirostris sp. nov. (Fig. 2B). The live colouration is also quite different between the two species. Jensen (2006) described the living colouration of L. mundus as: “Branchial region of carapace with irregular red spots; dorsal region with four short, narrow, evenly spaced electric blue bands. Abdomen with broad red bands separated by blue; telson and uropods reddish with no banding. Blue color tends to be faint or lacking in males. Walking legs reddish with widely spaced yellow bands; antennae orange, unbanded”. In the new species, the body and appendages are entirely orange-red, without distinct markings (Fig. 5). Lebbeus mundus has been recorded from the Pribilof Islands, Alaska to Octopus Hole, Hood Canal, Washington, at depths of 9–134 m (Jensen 2006).
Lebbeus saldanhae. Fransen (1997) redescribed L. saldanhae based on the holotype. The rostrum is slightly upturned with only three dorsal teeth, including one postrostral, in L. saldanhae (cf. Fransen 1997: fig. 50); in contrast, the rostrum is directed forward with an anteriorly sloping dorsal margin, which is armed with four or five teeth (including two postrostral ones) in L. parvirostris sp. nov. (Fig. 2A). The fourth pleonal pleuron is marginally rounded in L. saldanhae (cf. Fransen 1997: fig. 52), whereas it is armed with a tiny posteroventral tooth in L. parvirostris sp. nov. (Fig. 2G). According to the figure of Fransen (1997: fig. 52), although not specifically described, the second pleomere has a deep transverse groove like L. mundus, although such a deep transverse groove is absent in L. parvirostris sp. nov. (Fig.). Lebbeus saldanhae is so far known only from Saldanha Bay, South Africa, at a depth of 261 m (Fransen 1997).
Lebbeus schrencki. Jensen (2006) clarified that two species were mixed up in the three specimens constituting the syntypes of L. schrencki. No lectotype designation was made, and the identity of L. schrencki remains to be fixed. Nevertheless, according to Jensen (2006), all three specimens have six or seven dorsal teeth on the rostrum, three of which are postrostral in position. Indeed, the figure of Bražnikov (1907: fig. 21) shows the presence of three postrostral teeth on the carapace. In L. parvirostris sp. nov., there are only two postrostral teeth (Fig. 2A). The antennular stylocerite of L. schrencki extends to the end of the spine on the second article of the antennular peduncle; in L. parvirostris sp. nov. it reaches as far as the dorsodistal margin of the first article of the antennular peduncle (Fig. 2B). Bražnikov’s (1907: fig. 21) figure of L. schrencki also showed no indication of a notch inferior to the supraorbital spine on the carapace, which is an obvious feature of L. parvirostris sp. nov. (Fig. 2A). The syntypic specimens of L.schrencki came from the Sea of Okhotsk, at depths of 20– 49 m.
Lebbeus spongiaris. The rostrum bears only three dorsal teeth (two postrostral) in L. spongiaris (cf. Komai 2001: fig. 2B; Komai & Takeda 2004), rather than four or five (two postrostral) in L. parvirostris sp. nov. (Fig. 2A). The telson is armed only with two pairs of dorsolateral spiniform setae in L. spongiaris (cf. Komai 2001: fig. 2C; Komai & Takeda 2004), while three or four spiniform setae on either side in L. parvirostris sp. nov. (Fig. 2D). The antepenultimate article of the third maxilliped is armed with a distinct spine on the distolateral margin in L. spongiaris (cf. Komai 2001: fig. 3A), whereas such a spine is absent in L. parvirostris sp. nov. (Fig. 3A). Lebbeus spongiaris is known only from Sagami Bay and Izu Islands, central Japan, at depths of 228–698 m (Komai 2011).
Lebbeus tosaensis. The rostrum is armed with one or two teeth in L. tosaensis, rather than two or three in L. parvirostris sp. nov. The dactyli of the third to fifth pereopods are relatively more slender in L. tosaensis than in L. parvirostris sp. nov. (4.4–5.5 times as long as wide versus 3.5–3.7 times as long; Komai & Takeda 2004: fig. 4C versus Fig. 4B–D). The merus of the fifth pereopod is armed with three spiniform setae in L. tosaensis (cf. Hanamura & Abe 2003: fig. 3e; Komai & Takeda 2004), while only one spiniform seta is present on the merus of that pereopod in L. parvirostris sp. nov. (Fig. 3J). The live colouration is substantially different between the two species. Komai & Takeda (2004) described the living colouration of L. tosaensis as: “Carapace with 3 or 4 transverse vermilion bands; 1 similar band on each first to fifth abdominal somite; meri of third to fifth pereopods banded with white and vermilion, carpi to dactyli colorless”; whereas that of L. parvirostris sp. nov. is uniformly orange.
Besides the absence of an epipod on the third pereopod, Lebbeus brevicornis Komai, 2011 is also morphologically similar to the new species. Lebbeus parvirostris sp. nov. differs from L. brevicornis in the following particular characters: the rostrum bears two or three dorsal teeth in addition to two postrostral teeth in L. parvirostris sp. nov., instead of only one tooth in L. brevicornis (Komai 2011: fig. 6A); the anterolateral margin of the carapace has a deep notch just below the antennal spine in L. parvirostris sp. nov. (Fig. 2A), while such a notch is lacking in L. brevicornis (cf. Komai 2011: fig. 6A); the dactyli of the fourth and fifth pereopods are relatively stouter in L. parvirostris sp. nov. than in L. brevicornis (3.5–3.7 times as long as wide versus 5.9 times as long; Fig. 4B–D versus Komai 2011: fig. 7H).
In the holotype of Lebbeus parvirostris sp. nov., the carpi of the second pereopods are divided asymmetrically (seven segments in the left, nine segments in the right), while in the paratype, either carpus is divided into seven segments. The presence of seven segments is normal for species of Lebbeus as well as allied genera (e.g., Holthuis 1955, 1992; Butler 1980; Hayashi 1992). In the holotype, the second right pereopod is slightly shorter than the left one, suggesting that the one on the right side may be regenerated.
Genetic support. Barcoding regions of COI and 16S rRNA genes were sequenced from the holotype of L. parvirostris sp. nov. (Table 1). Unfortunately, genetic data are not available for the abovementioned morphologically similar species except for L. brevicornis. Due to differences in taxon coverage, preliminary phylogenetic analyses were performed separately for the COI and 16S rRNA datasets. Reconstruction using the COI dataset recovered L. parvirostris sp. nov. sister to L. brevicornis with strong support (bootstrap support = 98.7%) among the 24 named taxa available for the analysis (Fig. 6). Our tree recovered L. polaris as polyphyletic with genetically distinct clades, highlighting problems on the identity of L. polaris and these sequences, as already pointed out by previous works (Komai et al. 2021, 2022; Komai & Lemaitre 2023). The COI genetic divergence (K2P distance) between L. parvirostris sp. nov. and L. brevicornis was found to be 8.0% while the range of genetic divergence from other taxa included was 8.0-24.5% (Fig. 6; Appendix, Table A1), well-above the intraspecific variability range of 0–2.7% (excluding the problematic L. polaris). Phylogenetic reconstruction using the 16S rRNA gene (Fig. 7) agreed with the COI tree in suggesting that L. parvirostris sp. nov. is sister to L. brevicornis, although only with weak bootstrap support (<90%). The genetic divergence (K2P distance) between L. parvirotris sp. nov. and the 18 congeneric taxa available for the analysis was 1.6–7.0% (Fig. 7; Appendix, Table A2). Collectively, these results indicate that our new taxon is distinct from L. brevicornis (e.g., Ney et al. 2013; Komai et al. 2019, 2021, 2022; Marin 2020; Wang et al. 2023), and does not contradict recognizing it as a new species.
description: Published as part of Komai, Tomoyuki & Chen, Chong, 2024, A new species of the thorid shrimp genus Lebbeus White, 1847 (Decapoda: Caridea) from the Amami Rift hydrothermal vent field in the Ryukyu region, Japan, pp. 254-268 in Zootaxa 5523 (2) on pages 255-264, DOI: 10.11646/zootaxa.5523.2.7, http://zenodo.org/record/13934227