Lepechinella macrospinosa, Kodama & Mukaida & Hosoki & Jimi, 2025

Lepechinella macrospinosa sp. nov.

[New Japanese name: Toge-naga-gaikotsu-yokoebi]

( Figs 2–8 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

Material examined. Holotype: NSMT-Cr 32795 , 1 mature female, 11.3 mm, off Yakushima Island, Ryukyu Trench area , 29°35.3636N 130°40.8119E, 1,178m deep, on 28 Dec 2022, R/V Kaimei, beam trawl. GoogleMaps

Paratypes: all the paratypes were collected together with the holotype; NSMT-Cr 32796 , 1 mature female, 9.5 mm, INSDC LC860266 View Materials (COI, 658 bp); GoogleMaps NSMT-Cr 32797 , 1 immature female, 7.6 mm, INSDC LC860267 View Materials (COI, 630 bp); NSMT-Cr 32798 , 1 immature female, damaged (head lost), body length unknown, INSDC LC860268 View Materials (COI, 565 bp); NSMT-Cr 32799 , sex unknown, 6.2 mm .

Description. Based on holotype female (NSMT-Cr 32795, 11.3 mm), except for antennae 1, 2, and basis-dactylus of pereopod 7, which are damaged in holotype and the descriptions are based on paratype female (NSMTCr 32796, 9.5 mm).

Body ( Fig. 2A View FIGURE 2 ) laterally compressed, generally covered with sparse slender setae, often with small robust setae.

HEAD ( Fig. 2B–F View FIGURE 2 ). Rostrum ( Fig. 2F View FIGURE 2 ) almost straight, producing anterodorsally, reaching proximal 30% of antenna 1 peduncular article 1; first cephalic tooth produced anteriorly from slightly ventral to the base of antenna 1, about 0.5 times as long as rostrum; second cephalic tooth produced anteriorly from slightly dorsal to the base of antenna 2, about 0.3 times as long as rostrum. Eyes absent, at least cannot be observed under stereomicroscope or light microscope after two-month ethanol preservation. Antenna 1 damaged in holotype. Antenna 1 in paratype female ( Fig. 2B View FIGURE 2 ; NSMT-Cr 32796, 9.5 mm), length ratio of peduncular article 1–3 about 2: 5: 1.2, each article setose, but without robust setae; accessory flagellum ( Fig. 2C View FIGURE 2 ) consisting of 1 article, reaching about half of flagellar article 1, subdistally with 2 slender setae; flagellum longer than peduncle, several distal articles ( Fig. 2D View FIGURE 2 ) each with tiny sensory structure (possibly a kind of calceoli?). Antenna 2 damaged in holotype. Antenna 2 in paratype female ( Fig. 2E View FIGURE 2 ; NSMT-Cr 32796, 9.5 mm) longer than antenna 1, each article setose, but without robust setae, peduncular article 5 about 1.1 times as long as article 4; flagellum shorter than peduncle.

Mouth parts. Upper lip ( Fig. 3A View FIGURE 3 ), distal margin setose, separated by small incision, both lobes not produced. Lower lip ( Fig. 3B View FIGURE 3 ), damaged in holotype, distally setulose, mandibular process developed. Mandible ( Fig. 3C, D View FIGURE 3 ), left and right incisors 3 and 3-dentate, respectively; left and right lacinia mobilis 5 and 2-dentate, respectively; accessory setal row present; molar well developed; palp with 3 articles, length ratio of articles 1–3 about 2: 6: 3, article 1 bare, article 2 with two pairs of slender setae, article 3 with two distal slender setae. Maxilla 1 ( Fig. 3E View FIGURE 3 ), inner plate setulose, distally tapering with 3 plumose setae; outer plate setulose, lateral margin with 2 short setae near basal area of palp, distal margin obliquely truncate, with 9 dentate robust setae; palp with two article, article 1 short, bare, article 2 slightly expanded distally, lateral to distal margin rounded, medial margin slightly concave, distal to distomedial margin with 8 robust setae, ventral surface with 2 subdistal slender setae. Maxilla 2 ( Fig. 3F View FIGURE 3 ), inner plate setulose, slightly inward curved, distally rounded with group of long slender setae and thick plumose seta, medial margin with row of fine setae; outer plate slightly longer than inner plate, distally broadened, distally rounded with row of slender setae. Maxilliped ( Fig. 3G View FIGURE 3 ), inner plate, lateral margin roundly convex, medial margin straight, distal margin slightly oblique with 3 stubby setae, dorsal surface setulose, with 2 thick plumose setae and several slender setae; outer plate subrectangular, lateral margin convex, medial to distal margin with 10 robust setae, the robust setae on proximal side shorter and thicker, the robust setae on distal side thinner and longer, distalmost robust setae damaged in holotype, ventromedial margin with submarginal row of slender setae, dorsal surface setulose; palp elongate with 4 articles, length ratio of articles 1–4 about 2: 6: 2.5: 1 (unguis on article 4 ignored), article 1 with 2 slender setae on distomedial corner, article 2 elongate, reaching beyond distal end of outer plate, with row of long slender setae on medial margin and ventral surface, respectively, article 3 densely setose on distal half, article 4 short, with several short slender setae on distomedial corner, with strong terminal unguis, terminal unguis about 1.5 times as long as article 4.

PEREON. Pereonite 1 ( Fig. 2A View FIGURE 2 ) with two dorsal teeth, anterior tooth curved anteriorly, posterior tooth produced dorsally, almost straight; pereonites 2–6, each with dorsal tooth, each tooth almost straight, produced dorsally; pereonite 7 with larger tooth than that on pereonites 2–6, tooth produced and curved posteriorly.

Gnathopod 1 ( Fig. 4A, B View FIGURE 4 ) subchelate, slender, long; coxa deeper than wide, curved and produced anteriorly, distally tapering, not bifid, anterior margin concave, posteroventral margin rounded, both anterior and posterior margin with slender setae, ventral margin with small indistinct teeth on basal area of each setae; basis slender, elongate, slightly curved anteriorly, anterior margin slightly concave with row of long slender setae, posterior margin slightly convex with dense long slender setae; posterodistal corner with group of slender setae; ischium bare anteriorly, posterodistal corner with group of slender setae; merus short, bare anteriorly, posterior margin with sparse slender setae, distal margin oblique; carpus elongate, about 0.7 times as long as basis, anterior margin with dense groups of long slender setae in distal 70%, posterior margin and posteromedial surface covered with dense groups of long slender setae; propodus about 0.7 times as long as carpus, anterior margin straight to slightly convex with anterolateral and anteroventral slender setae, posterior margin roundly convex with several long robust setae, long and short slender setae, palm indistinct, medial surface with several lender setae, anterodistal corner with group of slender setae; dactylus about 0.7 times as long as propodus, tapering, curved, with anteroproximal small setae, anterior and posterior margin without teeth. Gnathopod 2 ( Fig. 4C, D View FIGURE 4 ) subchelate, slender; coxa deeper than wide, anterior margin convex with several short slender setae, anteroventral corner pointed, posteroproximal margin straight, posterior to central margin with slender setae, with pointed tooth; basis-dactylus larger than gnathopod 1; basis slender, elongate, slightly curved anteriorly, anterior margin slightly concave with row of long slender setae, posterior margin slightly convex with dense long slender setae; posterodistal corner with group of slender setae; ischium bare anteriorly, posterodistal corner with group of slender setae; merus sub-triangular, bare anteriorly, with sparse slender setae on posterior margin, distal margin oblique; carpus elongate, longer gnathopod 1 carpus, about 0.8 times as long as gnathopod 2 basis, rectilinear, anterior and posterior margins with groups of long setae, distal margin triangularly projected slightly overlapping proximal part of propodus; propodus about 0.5 times as long as carpus, anterior margin straight to slightly convex with anterolateral and anteroventral slender setae, posterior margin roundly convex with several long robust setae, long and short slender setae, palm indistinct, medial surface with several groups of slender setae, anterodistal corner with group of slender setae; dactylus about 0.7 times as long as propodus, tapering, curved, with anteroproximal small setae, anterior and posterior margin without teeth.

Pereopod 3 ( Fig. 5A View FIGURE 5 ) elongate, slender; coxa setose, anterior margin convex, ventral margin concave, posterior margin straight, anteroventral angle slightly produced ventrally, posteroventral corner rounded; basis rectilinear, anterior margin with row of robust setae, posterior margin with long setae and robust setae; ischium short, anteriorly bare, posterodistal corner with group of setae; merus-propodus, each segment rectilinear, anterior and posterior margins with robust setae, thick setae and slender setae; merus subequal or slightly shorter than basis, broader than carpus, anterodistal corner slightly produced distally; carpus about 0.7 times as long as merus, slightly broader than propodus; propodus with subequal length to carpus; dactylus elongate, about 1.3 times as long as propodus, tapering, curved, with subdistal short slender setae, dactylus slightly narrowed around distal area of the short setae. Pereopod 4 ( Fig. 5B View FIGURE 5 ) similar to pereopod 3 in shape, but slightly shorter than pereopod 3, posteroventral corner of coxa not produced like in pereopod 3 coxa, dactylus longer than pereopod 3 dactylus. Pereopod 5 ( Fig. 6A View FIGURE 6 ) coxa bilobate, anteroventral area produced ventrally into a pointed anterior lobe, baring short setae, posterior robe round, not produced, beringed long slender setae; basis, anterior margin rounded with several long slender setae in proximal 20%, straight in distal 80%, anterior and posterior margin with sparse robust setae, posteroproximal area with small brunt projection; merus-propodus, each segment rectilinear, anterior and posterior margins with sparse robust setae and slender setae; merus about 0.7 times as long as basis; carpus about 1.4 times as long as merus; propodus about 0.7 times as long as carpus; dactylus elongate about 1.4 times as long as propodus, curved, tapering, with subdistal short slender setae, anterior and posterior margins slightly narrowed around distal area of the short setae. Pereopod 6 ( Fig. 6B View FIGURE 6 ); coxa wider than deep, indistinctively bilobate, anterior lobe unproduced, deeper than wide with several short setae, posterior lobe rounded, wider then deep, slightly produced posteroventrally, with long slender setae; basis-dactylus similar to pereopod 5 in shape, but slightly longer than pereopod 5. Both left and right pereopod 7 lost in holotype except for coxa; pereopod 7 coxa ( Fig. 6C View FIGURE 6 ) parallelogram-form, anteroventral corner rounded with setae, ventral margin almost straight with slender setae in proximal half, posteroventral corner slightly produced backward, posterior margin with setae; basis-dactylus lost in holotype. Description for basis-dactylus based on paratype male (NSMT-Cr 32796, 9.5 mm; Fig. 6D View FIGURE 6 ), basis-dactylus slender, elongated; basis, anterior margin straight with sparse small setae, anterodistal corner with robust setae, posteroproximal corner with small projection, proximal margin straight, with sparse robust and slender setae; merus-propodus, each segment rectilinear, anterior and posterior margins with sparse robust setae and slender setae; dactylus elongate, tapering, curved, with subdistal short slender setae.

PLEON. Pleonites 1–3 ( Fig. 7A View FIGURE 7 ) each with strongly enlarged posterodorsal tooth, each tooth produced and curved posteriordorsaly, similar to each other in shape, but slightly differ in size, tooth on pleonite 1 largest, tooth on pleonite 3 smallest. Epimeral plate 1 ( Fig. 7A View FIGURE 7 ), anterior to ventral margin round, with row of long slender setae, posterior margin sinuous, slightly convex with small robust seta in dorsal area, concave in ventral area, posteroventral corner pointed, weakly produced backward; epimeral plate 2, ventral margin convex with several small robust setae, posterior margin excavated in ventral area, posteroventral angle pointed, produced backward; epimeral plate 3, ventral margin sinuous with small robust setae, anteroventral corner rounded with small robust setae, ventral margin with shallow excavation, posterior margin with acute excavation, posteroventral angle pointed, produced backward. Urosomite 1 produced posterodorsally into large and upward curved dorsal tooth; coalesced urosomites 2–3 slightly produced posteriorly into small dorsal tooth. Uropod 1 ( Fig. 7B View FIGURE 7 ) long, slender; peduncle, dorsolateral and dorsomedial margin with row of robust setae, ventrolateral margin with long slender setae in proximal 60% and several short setae distally, medial margin covered with dense fine setae; outer ramus about 0.6 times as long as peduncle, with dorsolateral and dorsomedial row of robust setae, distal area with group of robust setae; inner ramus shorter than outer ramus, about 0.4 times as long as peduncle, with dorsolateral and dorsomedial row of robust setae, distal area with group of robust setae, medial margin with dense fine setae. Uropod 2 ( Fig. 7C View FIGURE 7 ) shorter than uropod 1, not reaching distal end of uropod 1; peduncle, dorsolateral and dorsomedial margin with sparse long thick setae, ventrolateral margin bare, medial margin covered with dense fine setae; outer ramus about 0.6 times as long as peduncle, with dorsolateral and dorsomedial robust or thick setae, distal area with group of robust setae; inner ramus longer than outer ramus, about 0.7 times as long as peduncle, with dorsolateral and dorsomedial robust or thick setae, distal area with group of robust setae, medial margin with fine setae. Uropod 3 ( Fig. 7D View FIGURE 7 ) slender, elongated, almost reaching distal ends of uropod 2 rami; peduncle stout, short, lateral margin with fine setae, medial margin with several setae; rami long, subequal in length, margins with dense fine setae and sparse long thick setae, outer ramus with small second article bearing two long setae ( Fig. 7E View FIGURE 7 ). Telson ( Fig. 7F View FIGURE 7 ) longer than wide, reaching beyond distal end of uropod 3 peduncle, lateral margins slightly concave, posterior margin setose, strongly excavated into about 40% of total length, posterolateral corner produced roundly pointed, with long seta.

Distribution. Known only from type locality.

Etymology. The epithet of the new species “ macrospinosa ” refers to its strongly enlarged posterodorsal tooth on the pleonites 1–3.

Molecular data. Sequences of COI were determined from three paratypes (NSMT-Cr 32796, INSDC LC860266 View Materials , 658 bp; NSMT-Cr 32797, INSDC LC860267 View Materials , 630 bp; NSMT-Cr 32798, INSDC LC860268 View Materials , 565 bp). The maximum likelihood phylogenetic tree showed the sister clade of L. macrospinosa sp. nov. is L. skarphedini Thurston, 1980 , though it was supported by a low bootstrap value ( Fig. 9 View FIGURE 9 ), and the phylogenetic position of the species in the genus Lepechinella was not clear.

Remarks. The present new species is most closet to L. curvispinosa Pirlot, 1933 sharing the strongly enlarged and backward-curved posterodorsal tooth on the pleonites 1–3. However, L. macrospinosa sp. nov. can be distinguished from L. curvispinosa by the following characters: (1) the pereopod 5 carpus in mature female is distinctively longer (about 1.3 times longer) than the propodus in this new species ( Fig. 6A View FIGURE 6 ) [note: the length ratio of carpus to propodus show a variation with body length, from 1.1 times longer in the smallest individual (NSMT-Cr 32799) to>1.3 times longer in the largest individual (NSMT-Cr 32795)], whereas in L. curvispinosa , the pereopod 5 carpus is slightly longer (about 1.1 times longer) than the propodus even in mature female ( Pirlot 1933, figure 57PV); (2) the posterodorsal tooth on pleonite 3 is produced more dorsally in the new species (almost same shape with that on pleonites 1 and 2: Fig. 7A View FIGURE 7 ), whereas that of L. curvispinosa is produced more posteriorly (different shape from that on pleonites 1 and 2; the dorsal margin of the pleonite 3 extends posteriorly into the tooth without changing direction: Pirlot 1933, figure 55); (3) the posterodorsal tooth on the urosomite 1 is large and upward curved in the new species ( Fig. 7A View FIGURE 7 ), whereas that of L. curvispinosa is relatively smaller and not curved ( Pirlot 1933, figure 55); (4) the epimeral plates 1–3 are excavated in the posterior margin with a pointed tooth on the posteroventral corner in the present new species ( Fig. 7A View FIGURE 7 ), whereas those of L. curvispinosa are rounded without tooth ( Pirlot 1933, figure 55); (5) the uropod 3 is long, almost reaching the distal end of uropod 2 rami in this species ( Fig. 7A View FIGURE 7 ), whereas that of L. curvispinosa is short, just reaching the distal end of the uropod 2 peduncle ( Pirlot 1933, figure 55); (6) the uropod 3 rami are subequal in length in the present new species ( Fig. 7D View FIGURE 7 ), whereas in the L. curvispinosa , the inner ramus is distinctively longer than outer ramus ( Pirlot 1933, figure 57UIII).

In the Lepechinella species, the size and shape of dorsal teeth in the pereonites, pleonites and urosomites are known to change according to the size of specimens. In the present new species, the enlarged teeth on the pleonites are one of the diagnostic characters, and the shape of these teeth on the pleonites was almost static ( Figs 2 View FIGURE 2 , 8 View FIGURE 8 ) from the smallest specimen ( Fig. 8A View FIGURE 8 ; 6.2 View FIGURE 6 mm, NSMT-Cr 32799) to the largest specimen ( Fig. 2A View FIGURE 2 ; holotype, 11.3 mm, NSMT-Cr 32795). It is considered a useful character for species identification at least in this size range.

It is known in Lepechinella species that their eyes can fade and become unobservable after ethanol preservation ( Lörz et al. 2020). In the present new species, eyes were not observed at least in our examination. Our specimens were collected in Dec 2022 and first examined in detail in Feb 2023. It is not sure if the present new species is truly an eyeless species, or if their eyes have faded during the two-month ethanol preservation.