Lebbeus subtilis Komai & Matsuzaki 2022, n. sp.
Creators: name: Komai, Tomoyuki
name: Matsuzaki, Koji
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Thoridae
Lebbeus
Lebbeus subtilis

description: Lebbeus subtilis n. sp.
[New Japanese name: Sakura-ibara-mo-ebi]
(Figs. 5–8)
Material examined. Holotype. CBM-ZC 16698, ovigerous female (cl 15.9 mm), off Rausu, Nemuro Strait, 500– 800 m, 9 September 2015, commercial shrimp trap, coll. K. Matsuzaki, DNA voucher.
Diagnosis. Rostrum (Fig. 6A) somewhat curving dorsally, distinctly overreaching distal margin of antennal scaphocerite, 1.6 times as long as carapace; dorsal margin armed with 4 small teeth, including 2 on proximal 0.3 of rostrum and 2 postrostral (posteriormost tooth located at 0.3 of carapace length); ventral blade poorly developed, armed with 4 widely spaced teeth; tip simple, acuminate. Carapace (Fig. 6A) with low postrostral ridge; supraorbital spine small, arising at level of posterior margin of orbit; no notch below supraorbital spine; pterygostomial spine small; anterolateral margin between antennal and pterygostomial spines gently sinuous. Pleon (Fig. 6B) with pleura of anterior 3 pleomeres rounded, unarmed, that of pleomere 4 with angular posteroventral margin, that of pleomere 5 with strongly produced posteroventral spine.Telson (Fig. 7C, D) armed with 6 (right) or 9 (left) dorsolateral spiniform setae on either side; posterior margin rounded, with 2 pairs of unequal spiniform setae and some short setae on very narrow space. Antennular peduncle (Figs. 6A; 7A) slender, reaching distal 0.2 of scaphocerite; article 1 with small spine on dorsolateral distal angle; stylocerite falling short of distal margin of peduncular article 1, proximolateral lobe gently convex. Antenna (Figs. 6A; 7A, E) with scaphocerite 3.5 times as long as wide, distolateral spine far exceeded by distomesially produced, rounded lamella; carpocerite reaching midlength of scaphocerite. Maxilliped 3 (Fig. 8A) overreaching distal margin of antennal scaphocerite by half-length of ultimate article; ultimate article bearing row of 4 cuspidate setae distomesially (Fig. 7F). Pereopod 1 (Fig. 8B) relatively slender, reaching distal 0.2 of scaphocerite. Pereopod 3 (Fig. 8F) relatively slender, overreaching antennal scale by 0.6 length of propodus; dactylus (Fig. 7J) 0.13 times as long as propodus, 2.6 times longer than wide, with 6 narrowly spaced accessory spiniform setae on entire flexor margin; merus armed with 10 robust spiniform setae on lateral surface. Strap-like epipods on maxilliped 3 and pereopods 1 and 2, no epipod on pereopod 3 (Fig. 7M).
Description. Holotype. Body (Figs. 5, 6A, B) moderately stout; integument moderately firm, surface glabrous.
Rostrum (Fig. 6A) somewhat curving dorsally, distinctly overreaching distal margin of antennal scaphocerite, 1.6 times as long as carapace; dorsal margin armed with 4 small teeth including 2 on rostrum proper (anteriormost tooth located at proximal 0.3 of rostral length, and then anterior 0.7 leaving unarmed) and 2 postrostral (posteriormost tooth located at 0.3 of carapace length); ventral blade very narrow, deepest at 0.3 length, margin armed with 4 subequal teeth more widely spaced anteriorly; lateral carina obsolete. Carapace (Fig. 6A) with low postrostral ridge extending beyond midlength of carapace length, becoming broader and blunt posteriorly; dorsal profile in lateral view nearly straight; orbital margin evenly concave, ventral part limbed marginally (Fig. 7B), postorbital region shallowly depressed; supraorbital spine small, arising at level of posterior margin of orbit; no notch below supraorbital spine; suborbital lobe distinct, rounded (Fig. 7B); antennal spine small, well exceeding beyond suborbital lobe; pterygostomial spine small, directed anteroventrally; anterolateral margin between antennal and pterygostomial spines gently sinuous; no conspicuous ridges on lateral surface.
Pleon (Fig. 6B) with pleura of anterior four pleomeres rounded, unarmed, that of pleomere 5 with strong posteroventral spine. Pleomere 2 tergum with deep transverse groove. Pleomere 3 rounded dorsally, posterodorsal margin somewhat produced posteriorly. Pleomere 6 1.7 times as long as pleomere 5, 2.4 times as long as high, with small posteroventral spine and posterolateral process terminating in small spine. Telson (Fig. 7C, D) reaching slightly beyond posterior margin of uropods, 1.5 times as long as pleomere 6, relatively narrow, armed with 6 (right) or 9 (left) dorsolateral spiniform setae; posterior margin triangular, with 2 pairs of unequal spiniform setae (mesial pair longer and stouter than lateral pair) and several short setae on very narrow median space.
Eye (Figs. 6A; 7A) subpyriform; cornea darkly pigmented, its maximum width about 0.24 of carapace length; ocellus absent. Eyestalk short, cup-shaped.
Antennular peduncle (Figs. 6A; 7A) slender, reaching distal 0.2 of antennal scaphocerite. Article 1 longer than distal two articles combined, with small spine on dorsolateral distal angle; stylocerite moderately slender, partially in touch with first article mesially, slightly curving dorsally, terminating in acute spine falling far short of distal margin of peduncular article 1, proximolateral lobe with small tubercle, making proximolateral lobe as hooklike projection. Article 2 subcylindrical, armed with small spine at dorsolateral distal angle. Article 3 short, with small spine on dorsodistal margin. Upper flagellum with thickened aesthetasc-bearing portion 0.4 times as long as carapace; lower flagellum distinctly longer than upper flagellum.
Antenna (Figs. 6A; 7A, E) with moderately stout basicerite, bearing blunt dorsolateral projection and slender ventrolateral spine. Scaphocerite 0.9 times as long as carapace, 3.5 times as long as wide; lateral margin nearly straight; distolateral spine relatively slender, far exceeded by distomesially produced, rounded lamella. Carpocerite reaching midlength of scaphocerite.
Mouthparts not dissected. Maxilliped 3 (Fig. 8A) relatively slender, overreaching distal margin of antennal scaphocerite by 0.5 length of ultimate article; ultimate article 3.7 times as long as penultimate article, bearing 8, including 4 on mesial margin, darkly pigmented cuspidate setae partially circumscribing terminal margin (Fig. 7F); antepenultimate article subequal in length to ultimate article, with 1 minute spiniform seta at ventrolateral distal angle, dorsodistal margin unarmed, distolateral margin with 1 tiny spine (Fig. 7G); exopod absent.
Pereopod 1 (Fig. 8B; C) relatively slender, reaching midlength of scaphocerite. Chela 1.3 times as long as carpus, 5.7 times as long as wide; dactylus 0.6 times as long as palm, terminating in 2 black corneous claws and slender, accessory claw at base of shorter terminal claw (Fig. 7H); fixed finger terminating in single black claw (Fig. 7H); palm 3.6 times as long as wide, with short row of grooming setae on mesial face proximally. Carpus subcylindrical; grooming apparatus consisting of rows of stiff setae circumscribing deep depression on subdistal portion on dorsal face and subdistal cluster of short stiff setae on mesial face. Merus 7.7 times as long as wide, with minute spine on near dorsal margin proximally and few minute spiniform setae on ventral margin proximally (Fig. 7I). Ischium with cluster of minute spiniform setae on ventrodistal margin (Fig. 7I).
Pereopod 2 (Fig. 8D) moderately slender, overreaching distal margin of scaphocerite by length of chela. Chela slightly less than 0.2 times as long as carpus, with tufts of short setae on fingers; dactylus 0.4 times as long as palm. Carpus subdivided into 7 segments, length ratio of segments: 1: 0.6: 2.7: 0.8: 0.6: 0.4: 0.8; distalmost segment with prominent tuft of setae. Merus 1.2 times as long as ischium.
Pereopod 3–5 (Fig. 8E–G) relatively slender. Pereopod 3 (Fig. 8E) overreaching scaphocerite by 0.6 length of propodus; dactylus (Fig. 7J) short, 0.13 times as long as propodus, 2.6 times longer than wide, terminating in moderately slender, clearly demarcated unguis, with 6 accessory spiniform setae on entire flexor margin, increasing in length distally, distalmost accessory seta slightly curved; propodus 20 times longer than wide, with evenly spaced minute spiniform setae arranged in 2 rows on flexor margin; carpus 0.6 times as long as propodus, unarmed: merus 13 times longer than wide, armed with 10 robust spiniform setae on lateral surface; ischium unarmed. Pereopod 4 (Fig. 8F) similar to pereopod 3, overreaching antennal scale by 0.2 length of propodus; dactylus (Fig. 7K) with 6 accessory spiniform setae; merus with 8 robust spiniform setae on lateral surface. Pereopod 5 (Fig. 8G) generally similar to pereopods 3 and 4, overreaching antennal scale by length of dactylus; dactylus (Fig. 7L) with 6 accessory spiniform setae; propodus with cluster of grooming setae on flexor surface in distal 0.1 of flexor margin; merus with 4 robust spiniform seta on lateral face.
Strap-like epipods present on maxilliped 3 and pereopods 1 and 2; anterior 2 epipods terminally hooked, interacting with setobranchs on pereopods 1 and 2, respectively; epipod on pereopod 2 simple, no corresponding setobranch on pereopod 3 (Fig. 7M).
Pleopods without distinctive features.
Uropod (Figs. 6B; 7C) reaching posterior margin of telson. Protopod terminating in strong acute spine posterolaterally. Exopod subequal in length of endopod, with small posterolateral spine exceeded by tiny spiniform seta arising at its mesial base.
Eggs oval, large, 2.4× 3.5 mm.
Colouration in life. Carapace and rostrum pale pink, tip of rostrum reddish; pleon also pale pink generally, pleomeres 1 to 3 each with irregular red transverse band medially, pleomeres 4 and 5 each with red transverse band posteriorly; pleomere 6 with red tint posteriorly; tail fan (telson and uropods) reddish; cornea black; antennular and antennal peduncles generally pinkish, antennal carpocerite red; flagella uniformly pink or reddish; maxilliped 3 antepenultimate and penultimate articles reddish proximally and distally, otherwise white, penultimate article red, with white blotch; pereopod 1 pink to red, fingers red; pereopod 2 ischium and merus mottled with pink and red; carpus and chela pale pink; pereopods 3–5 ischia and meri mottled pink and red; carpi and propodi generally white, but latter articles with tint of red distally; dactyli red; pleopods 2–5 generally pale pink, ventral expansions of protopods each with proximal red and distal white blotches; eggs yellow (Fig. 5).
Distribution. Presently known only from off Rausu, Nemuro Strait, at depth of 500– 800 m.
Remarks. Lebbeus subtilis n. sp. is referred to the species group characterised by having epipods on the maxilliped 3 and pereopods 1 and 2, represented by 23 previously described species (cf. Table 1). The new species is characteristic in having an elongate rostrum being distinctly longer than the carapace, with a poorly developed ventral lamina and a greatly unarmed dorsal margin (the distal 0.6 is unarmed). None of the other species in this group has such an elongate rostrum with few dorsal teeth and a poorly developed ventral lamina (cf. Kobjakova 1937; Zarenkov 1960; Wicksten & Méndez 1982; Kensley et al. 1987; Hayashi 1992; Crosnier 1999; Komai 2002; Jensen 2006; McCallum & Poore 2010; Komai et al. 2012, 2016, 2021).
Morphologically, Lebbeus subtilis n. sp. is rather similar to L. fujimotoi and L. rufomaculosus n. sp. in the general body form and the shape and armature of the rostrum, although the development of pereopodal epipods is different among those species. The present new species differs from L. fujimotoi in having fewer ventral teeth on the rostrum (four versus seven to nine), the antennular stylocerite falling short of the distal margin of the peduncular article 1 (versus reaching it) (cf. Fig. 7A versus Matsuzaki et al. 2015: fig. 3A, B) and the presence of epipods on the pereopods 1 and 2 (versus epipods are usually absent on those pereopods) (cf. Fig. 7M versus Matsuzaki et al. 2015: fig. 3F). The absence of a prominent proximolateral projection on the antennular stylocerite immediately distinguishes L. subtilis n. sp. from Lebbeus rufomaculosus n. sp. (cf. Fig. 6A versus Fig. 3E). Furthermore, L. subtilis n. sp. differs from L. rufomaculosus n. sp. in the more stout dactyli of the pereopods 3–5 (Fig. 7J–L versus Fig. 3J–L) and the presence of an epipod on the pereopod 2 (versus epipod absent on pereopod 2) (Fig. 7M versus Fig. 3M).
The status of L. subtilis n. sp. is well supported by the genetic analyses: COI divergence between L. subtilis n. sp. and the known congeneric species ranges from 4.2 to 19.6% (Table 3); 16S divergence ranges from 2.1 to 7.6% (Table 4).
Etymology. From the Latin “ subtilis ” (= slender), in reference to the slender rostrum with a poorly developed ventral lamina.
description: Published as part of Komai, Tomoyuki & Matsuzaki, Koji, 2022, Three new species of the thorid shrimp genus Lebbeus White, 1847 (Decapoda: Caridea) from Nemuro Strait, Hokkaido, Japan, with supplemental note on L. fujimotoi Matsuzaki, Hibino & Komai, 2015, pp. 151-181 in Zootaxa 5133 (2) on pages 162-167, DOI: 10.11646/zootaxa.5133.2.1, http://zenodo.org/record/6521560