Lobatoradarea lignorum Ariyama & Moritaki, 2025

Lobatoradarea lignorum Ariyama & Moritaki , sp. nov.

[New Japanese name: Chimboku-udenaga-yokoebi]

( Figs 36–41)

Type material. Holotype: ovigerous female, 7.1 mm (OMNH-Ar-13242), Kumano-nada, off Owase City in Mie Prefecture ( Fig. 1H), 310–320 m deep, inhabiting sunken wood, using a commercial trawl net, 27 October 2019 (reared continuously in aquarium until 2 November 2023), coll. Takeya Moritaki. Paratypes: 6 ovigerous females, 7.3, 7.0, 6.8, 6.4, 6.2, 5.6 mm (OMNH-Ar-13243–13248), 1 female, 7.1 mm (OMNH-Ar-13249), and 2 males, 5.3, 4.4 mm (OMNH-Ar-13250, 13251), same data as holotype .

Type locality. Kumano-nada , off Owase City in Mie Prefecture, Japan .

Etymology. From the Latin lignorum (=wood), referring to the habitat of this species. Used as noun in apposition.

Description of female. Based on holotype, ovigerous female, 7.1 mm (OMNH-Ar-13242), paratype, ovigerous female, 7.0 mm (OMNH-Ar-13244) for lower lip, and paratype, ovigerous female, 6.2 mm (OMNH-Ar-13247) for uropods 1, 2.

Head ( Figs 36, 37). Rostrum developed, lateral cephalic lobe rounded, anteroventral corner slightly projected. Eyes oval, medium-sized (diameter: 37% of head height). Antenna 1, peduncular articles 1–3 with length ratio of 1.0: 0.7: 0.2; accessory flagellum short, cylindrical, with 3 setae on tip; primary flagellum long, with 59 articles, article 1 relatively long, aesthetascs absent. Antenna 2 longer than antenna 1, peduncular articles 3–5 with length ratio of 1.0: 2.6: 3.8, each article bearing several setae; flagellum long, with 71 articles, article 1 long. Upper lip relatively long, produced ventrally, anterior surface and ventral margin with many minute setae. Mandibles, incisors with 9 and 8 cusps in left and right, respectively, laciniae mobilis 8- and 3-toothed in left and right, respectively, accessory setal rows with 5 and 4 thick setae in left and right, respectively; palp stout, article length ratio 1.0: 3.7: 2.2 in left, article 1 short, bare, article 2 long, with 4–5 setae subdistally, article 3 bearing 1 proximal, 9 ventral and 1 thick and 2 slender distal setae, lateral and medial surfaces covered with dense thin setae. Lower lip, inner lobes large, bare; outer lobes triangular, with relatively long mandibular lobes, setose mediodistally, ventral surfaces and lateral margins with sparse fine setae. Maxilla 1, inner plate pear-shaped, medial margin bearing long plumose setae; outer plate distally with 11 denticulate robust setae and many slender setae; palp article 1 bare, article 2 apically with 7 triangular robust setae and 4 slender setae in left and 7 narrow robust setae and 5 slender setae in right. Maxilla 2, inner plate wide, ca. 1.7 times width of outer plate. Maxilliped, inner plate with 3 triangular robust setae distally; outer plate bearing 4 long and 9 short robust setae mediodistally; palp article 3 dorsal surface with 4 thick setae and many fine setae.

Pereon ( Figs 36, 38). Pereonite 7 with strong projection posterodorsally. Gnathopod 1 relatively short; coxa subrectangular, with a small notch each on anteroventral and posteroventral corners, medial surface bearing many setae; basis slender, straight, anterior margin lined with short setae, posterior margin bearing 8 long setae, medial surface setose anteriorly; merus acutely projected distally, with several setae on posterodistal margin; carpus relatively long, posterior margin bearing many thick setae; propodus slightly longer than carpus (ca. 1.1 times), posterior margin with several thick setae and many slender setae, palm weakly oblique, defined by 5 (3 lateral and 2 medial) short robust setae; dactylus short. Gnathopod 2 longer than gnathopod 1; coxa roundish trapezoidal, with a small notch each on anteroventral and posteroventral corners, medial surface bearing 2 setae; basis slender, straight, anterior margin lined with short setae, posterior margin bearing 7 long setae; merus acutely projected distally, posterodistal corner with 2 short setae; carpus long and narrow, posterior margin bearing several bundles of slender setae; propodus longer than carpus (ca. 1.25 times), narrow, anterior margin lined with short setae, posterior margin bearing many bundles of slender setae, palm weakly oblique, defined by 4 (2 lateral and 2 medial) short robust setae; dactylus short. Pereopod 3, coxa roundish rectangular, with 2 and 4 small notch on anteroventral and posteroventral corners, respectively, medial surface bearing several setae; basis almost straight, anterior margin and anterodistal corner with 6 and 3 robust setae, respectively, anteroproximal and posteroproximal margins with several slender setae; merus anterior margin and anterodistal corner each with a robust seta; carpus posterior margin with 4 robust setae; propodus longer than carpus, posterior margin and posterodistal corner with 5 and 2 robust setae, respectively; dactylus smooth. Pereopod 4, coxa ventral margin slightly angular, with 4 and 6 small notches on anteroventral and posteroventral margins, respectively, medial surface bearing many setae; basis almost straight, anterior margin and anterodistal corner with 3 and 2 robust setae, respectively, anteroproximal and posteroproximal margins with several slender setae; ischium–merus similar to those of pereopod 3; carpus–dactylus lost. Pereopod 5, coxa anteroventral margin with 3 small notches, posterior and posteroventral margins with 3 and 2 small notches, respectively, medial surface bearing several setae anteriorly; basis ovoid, with anterolateral ridge, anterior margin with a few proximal setae and 7 robust setae, posterior margin minutely serrated, medial surface with vertical ridge bearing a robust seta and several setae; merus with 3 anterior, 3 anterodistal, 4 posterior and 4 posterodistal robust setae; carpus–dactylus lost. Pereopod 6 long; coxa anterior margin slightly concave, with 7 setae, posterior and posteroventral margins each with 2 small notches; basis ovoid, with anterolateral ridge, anterior margin with several proximal setae and 5 robust setae, posterior margin minutely serrated, medial surface with vertical ridge bearing a robust seta; merus with 2+2+2 anterior, 3 anterodistal, 7 posterior and 4 posterodistal robust setae; carpus with 1+3+3+2 anterior, 4 anterodistal, 1 posterior and 5 posterodistal robust setae; propodus with 1+2+2+2+2+2 anterior, 3 anterodistal and 3 posterior robust setae; dactylus smooth. Pereopod 7 almost same length as pereopod 6 (probably partly regenerated); coxa short, anterior margin with 4 setae, posteroventral margin with 2 small notches; basis ovoid, with anterolateral ridge, anterior margin with many proximal setae and 4 (1 lost) robust setae, anterodistal corner bearing a robust seta, posterior margin minutely serrated, medial surface with a robust seta; merus with 1+2+3 anterior, 3 anterodistal, 5 posterior and 4 posterodistal robust setae; carpus with 1+2+2+2 anterior, 4 anterodistal, 2 posterior and 3 posterodistal robust setae; propodus with 2+2+2+2+2+2+1 anterior, 3 anterodistal and 2 posterior robust setae; dactylus smooth.

Pleon ( Figs 36, 39). Pleonites 1, 2 strongly projected posterodorsally. Epimeral plates 1–3, posteroventral corners minutely produced, lateral surfaces of plates 1, 2 with ridge, ventral margins of plates 2, 3 bearing 2 and 3 robust setae, respectively. Pleopods, pleopod 2 longest; each peduncle bearing many setae and 2 coupling hooks, peduncle of pleopod 1 with a robust seta posteromedially, peduncle of pleopod 3 bearing 5 posteromedial and 2 lateral robust setae; both rami almost same length, outer rami with 13, 14, 15 articles and inner rami with 12, 13, 13 articles in pleopods 1–3, respectively. Uropod 1, peduncle long, dorsal surface with 8 lateral, 1 laterodistal, 3 medial and 1 mediodistal robust setae, ventrodistal end slightly produced; outer ramus ca. 0.65 times length of peduncle, with 4 lateral and 4 (1 lost) terminal robust setae; inner ramus ca.1.7 times as long as outer ramus, with 7 lateral, 6 (2 lost) medial and 4 terminal robust setae. Uropod 2 about 0.8 times as long as uropod 1; peduncle short, with 3 lateral, 1 laterodistal, 2 medial and 1 mediodistal robust setae, ventrodistal end slightly produced; outer ramus ca. 0.8 times length of peduncle, with 3 lateral and 4 (1 lost) terminal robust setae; inner ramus ca. 2.15 times as long as outer ramus, with 8 lateral, 8 medial and 4 terminal robust setae. Uropod 3, peduncle very short, longer than wide, bare, ventrodistal end triangularly produced, medial margin with 3 short setae; outer ramus ca. 1.6 times length of peduncle, with 8 lateral and 6 medial robust setae; inner ramus about 1.75 times as long as outer ramus, with 2 proximal, 11 lateral and 13 medial robust setae. Telson small, trapezoidal, distal margin rounded, dorsal surface with 6 sensory setae, lateral margins bearing several minute setae.

Description of male. Based on paratype, male, 5.3 mm (OMNH-Ar-13250). Almost similar to holotype, ovigerous female, 7.1 mm (OMNH-Ar-13242) except for oostegites. Gnathopods resembling those of female; but gnathopod 1 coxa lacking anteroventral notch and medial surface of basis bearing fewer setae, propodus with 3 (2 lateral and 1 medial) posterodistal robust setae ( Fig. 39 M-G1), and gnathopod 2 coxa with 2 posteroventral notches, propodus bearing 3 (2 lateral and 1 medial) posterodistal robust setae ( Fig. 39 M-G2).

Coloration in life. Based on specimens reared in the aquarium ( Figs 40, 41). Head, pereonites, pleonites, all coxae and bases of pereonites 5–7 pale pinkish orange (pink ovary seen through in females); eyes bright red, urosomites and other appendages translucent.

Remarks. Lobatoradarea lignorum sp. nov. is characterized by a combination of the strong projection on the pereonite 7 and the smooth dactyli of the pereopods 3–7. This combination is shared with L. angulata sp. nov.; however, this new species can be distinguished from L. angulata by the smaller eyes and the rounded ventral margin of the coxa 4. Although Lobatoradarea longimana also has such dactyli of the pereopods 3–7, the projection on the pereonite 7 of L. longimana is indistinct or absent ( Shoemaker 1930, fig. 35).

Habitat. On the surface of sunken wood on relatively deep bottom ( 310–320 m depth).

Distribution. Japan: Kumano-nada (present study).

Behavior observed in the aquarium. Lobatoradarea lignorum sp. nov. inhabits the surface of sunken wood in a group including juveniles ( Fig. 41). Each individual moves around, but distinct digging, feeding or mating behaviors have not been observed. This species can be maintained alive for a substantial period easily, even when without any food.