Lebbeus dentatus, Wang & Sha, 2024

Wang, Yan-Rong & Sha, Zhong-Li, 2024, Lebbeus dentatus n. sp. (Decapoda, Thoridae) described from a seamount of the Caroline Plate, NW Pacific, Zootaxa 5468 (1), pp. 191-200 : 192-196

publication ID	https://doi.org/ 10.11646/zootaxa.5468.1.9
publication LSID	lsid:zoobank.org:pub:980D6E63-6433-4A3F-B970-C34C31CEC157
DOI	https://doi.org/10.5281/zenodo.11616903
persistent identifier	https://treatment.plazi.org/id/AE2C87C7-FFEF-FF96-FF68-CC78FCEAD961
treatment provided by	Plazi
scientific name	Lebbeus dentatus
status	sp. nov.

Treatment

Lebbeus dentatus n. sp.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Material examined. Holotype. MBM 287876 View Materials , not ovigerous female (cl 8.3 mm), unnamed seamount on Caroline Plate, NW Pacific, M5422, 10°05′N 140°11′E, depth 844–998 m, 3 June 2019. GoogleMaps

Description. Body ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ) moderately slender; integument surface glabrous.

Rostrum ( Figs. 2A, B View FIGURE 2 , 3A View FIGURE 3 ) nearly straight, reaching to distal margin of second article of antennular peduncle; dorsal margin armed with 4 rather strong teeth, anteriormost tooth on anterior to base of rostrum, posteriormost tooth arising at about 0.5 of carapace length; ventral margin armed with 2 teeth in distal 0.3; lateral carina absent. Carapace ( Figs. 2A View FIGURE 2 , 3A View FIGURE 3 ) with distinct postrostral ridge extending to three-fourths of carapace. Supraorbital tooth unusually strong, arising at level of posterior margin of orbit, directed forward, reaching proximal 0.3 of rostrum, distinctly overreaching antennal tooth in lateral view; suborbital lobe distinct, subtriangular; antennal tooth moderately slender; pterygostomial tooth subequal to antennal tooth; anterolateral margin between antennal and pterygostomial teeth faintly sinuous.

Pleon ( Fig. 2A View FIGURE 2 ) with pleura of anterior three pleomeres rounded, those of fourth and fifth pleomeres each with sharp posteroventral tooth. Third pleomere rounded dorsally, posterodorsal margin moderately produced posteriorly. Sixth pleomere about 1.8 times as long as fifth pleomere, 1.8 times as long as high, with small posteroventral tooth and sharply pointed posterolateral process. Telson ( Fig. 3C View FIGURE 3 ) narrow, armed with 4 pairs of dorsolateral spines; posterior margin armed with 2 pairs of unequal lateral spines (mesial pair longer and stouter than lateral pair).

Eye ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ) subpyriform. Cornea large, darkly pigmented, its maximum width 0.22 of carapace length; ocellus absent. Eyestalk short, cup-shaped.

Antennular peduncle ( Figs. 2A View FIGURE 2 , 3A, B View FIGURE 3 ) moderately slender, reaching distal 0.3 of antennal scaphocerite. Article 1 longer than distal two articles combined, with acute spine and subtriangular process on lateral distal margin; stylocerite slender, hardly reaching to distal margin of peduncular article 2; no proximolateral projection. Article 2 longer than article 3, with single large distolateral spine. Article 3 with small spine on dorsodistal margin. Lateral flagellum with thickened aesthetasc-bearing portion approximately less than half-length of carapace; lower flagellum distinctly longer than upper flagellum.

Antenna ( Figs. 2C View FIGURE 2 , 3A View FIGURE 3 ) basicerite with moderately rounded dorsolateral tooth distinctly shorter than sharp ventrolateral tooth. Antennal scale 0.9 times as long as carapace; lateral margin slightly concave; distolateral tooth sharp, distinctly overreaching rounded distal margin of lamella. Carpocerite hardly reaching midlength of antennal scale.

Mouthparts not dissected. Third maxilliped ( Fig. 3D View FIGURE 3 ) moderately slender, overreaching distal margin of antennal scale by 0.25 length of ultimate segment. Ultimate segment about 3.1 times as long as penultimate segment; distal portion bearing 8 corneous spines. Antepenultimate segment shorter than distal two segments combined, unarmed. Exopod absent. Coxa with strap-like epipod ( Fig. 2A View FIGURE 2 ).

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

First pereopod ( Fig. 3E, F View FIGURE 3 ) relatively slender. Chela 1.7 times longer than carpus; distal part of fingers with few tufts of stiff setae; dactylus about 0.8 times as long as palm, terminating in 2 corneous claws, outer claw shorter than inner claw; fixed finger terminating in single corneous claw. Carpus slightly widened distally, subequal in length to palm, inner surface with spinules ( Fig. 3F View FIGURE 3 ). Merus with short row of spiniform setae on ventral margin proximally. Ischium with row of spiniform setae on ventral margin.

Second pereopod ( Fig. 3G View FIGURE 3 ) moderately slender, overreaching antennal scale by length of distal two carpal articles and chela. Chela about 0.3 times as long as carpus. Carpus subdivided into 7 articles, third article longest, occupying about 0.3 times whole carpal length. Merus about 0.8 times as long as ischium.

Third to fifth pereopods generally similar in structure and ornamentation. Third pereopod ( Fig. 3H View FIGURE 3 ) overreaching antennal scale by about 0.7 length of propodus. Dactylus 0.2 times as long as propodus, terminating in slender, darkly pigmented unguis, bearing 5 darkly pigmented accessory spinules on flexor margin, distalmost accessory spinule subterminal, distinctly larger and wider at base than others, making tip of dactylus appearing biunguiculate. Propodus with rows of slender spinules on flexor surface. Carpus 0.4 times as long as propodus, unarmed. Merus armed with 4 lateral spines. Ischium unarmed.

Fourth pereopod ( Fig. 3I View FIGURE 3 ) overreaching antennal scale by about 0.3 length of propodus; dactylus similar to that of third pereopod; carpus 0.4 times as long as propodus merus armed with 2 lateral spines. Fifth pereopod ( Fig. 3J View FIGURE 3 ) reaching antennal scale by tip of propodus; dactylus about 0.2 length of propodus, with 5 accessory spinules; propodus with cluster of grooming setae on flexor surface distally; merus with 1 subdistal lateral spine.

Colouration in life. Anterior part of carapace reddish; proximal part of carapace, pleon and tail fan (telson and uropods) transparent white with obscure reddish streaks on each of pleomeres 1–6; cornea darkly pigmented with red dot; third maxilliped to pereopod 3 reddish; pereopods 4 and 5 transparent.

Distribution. Presently known only from unnamed seamount on Caroline Plate at depth of 844– 998 m.

Etymology. From the Latin “ dentatus ” (=tooth), in reference to the large supraorbital tooth in the new species.

Remarks. Lebbeus dentatus n. sp. is referred to the species group characterized by having epipods on the pereopods 1 and 2, represented by 23 previously described species ( Komai & Matsuzaki 2022). The new species is characteristic in having unusually strong supraorbital tooth, which far overreaching antennal tooth. Only two species in this species group has such large supraorbital tooth, including L. brevirostris Chang, Komai & Chan, 2010 and L. laevirostris Crosnier, 1999 (cf. Kobjakova 1936; Zarenkov 1960; Wicksten & Méndez 1982; Kensley et al. 1987; Hayashi 1992; Crosnier 1999; Jensen 2006; Chang et al. 2010; McCallum & Poore 2010; Wicksten 2010; Komai 2011; Komai et al. 2012, 2016, 2021; Komai & Matsuzaki 2022).

Morphologically, Lebbeus dentatus n. sp. differs from L. brevirostris in: the moderately long rostrum barely extending to the end of antennular peduncle, and bearing 2 ventral teeth nearly apex ( Figs. 2 View FIGURE 2 , 3A View FIGURE 3 ), while the spiniform rostrum not extending to midlength of first article of antennular peduncle and unarmed ventrally in L. brevirostris ( Chang et al. 2010, Fig. 1A, B View FIGURE 1 ); the fourth pleomere with sharp posteroventral tooth ( Fig. 2 View FIGURE 2 ), while rounded in L. brevirostris (cf. Chang et al. 2010: Fig. 1D View FIGURE 1 ). Similarly, the moderately long and denticulate rostrum immediately distinguishes L. dentatus n. sp. from L. laevirostris ( Crosnier 1999, Figs. 1 View FIGURE 1 , 3A View FIGURE 3 ).

Unfortunately, molecular markers of the aforementioned two species ( L. brevirostris , L. brandti and L. laevirostris ) are not available ( Table 1 View TABLE 1 ). Even so, the status of Lebbeus dentatus n. sp. is well supported by the genetic analyses: COI divergence between L. dentatus n. sp. and the known congeneric species ranges from 14%– 19% ( Table 2 View TABLE 2 ); 16S divergence ranges from 5%–7% ( Table 3 View TABLE 3 ).