Lobatoradarea littoralis Ariyama, 2025

Lobatoradarea littoralis Ariyama , sp. nov.

[New Japanese name: Kishi-udenaga-yokoebi]

( Figs 2–6)

Type material. Holotype: ovigerous female, 4.9 mm (OMNH-Ar-13204), Tagurasaki coast, Wakayama City , Wakayama Prefecture, 34°16'02"N, 135°03'39"E ( Fig. 1F), uppermost subtidal, under stones, 30 June 2007, coll. Hiroyuki Ariyama. GoogleMaps Paratypes: 2 ovigerous females, 5.0, 4.4 mm (OMNH-Ar-13205, 13206), 3 males, 4.4, 3.7, 3.2 mm (OMNH-Ar-13207–13209), same data as holotype; female, 4.2 mm (OMNH-Ar-13210), Toyokunizaki coast, Misaki Town , Osaka Prefecture, 34°19'22"N, 135°07'00"E ( Fig. 1G), 2 m depth, coarse sand bottom with shells, 19 July 2020, coll. Hiroyuki Ariyama. GoogleMaps

Type locality. Tagurasaki , Wakayama City in Wakayama Prefecture, Japan .

Etymology. From the Latin littoralis , -is, -e (=littoral), referring to the habitat. Adjective.

Description of female. Based on holotype, ovigerous female, 4.9 mm (OMNH-Ar-13204) and paratype, ovigerous female, 5.0 mm (OMNH-Ar-13205) only for maxilla 1.

Head ( Figs 2, 3). Rostrum developed, lateral cephalic lobe rounded, anteroventral corner slightly projected. Eyes small (diameter: 23% of head height). Antenna 1, peduncular articles 1–3 with length ratio of 1.0: 0.6: 0.3; accessory flagellum very short, bullet-shaped, with 4 setae; primary flagellum with 37+ articles, tip lost, article 1 relatively long, 8 articles with aesthetasc. Antenna 2, peduncular articles 3–5 with length ratio of 1.0: 2.6: 2.7, each article bearing several robust setae; flagellum long, with 44+ articles, tip lost, article 1 long. Upper lip weakly produced ventrally, bearing many minute setae. Mandibles, incisors with 7 and 10 cusps in left and right, respectively, laciniae mobilis 10- and 3-toothed in left and right, respectively, both accessory setal rows with 5 thick setae; palp stout, article length ratio 1.0: 3.5: 2.7, article 1 short, bare, article 2 long, with 3 setae subdistally, article 3 bearing 8 ventral setae and 1 thick and 2 slender distal setae, lateral surface covered with dense thin setae. Lower lip, inner lobes developed, bare; outer lobes 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 several thick setae; palp article 1 bare, article 2 apically with 5 triangular and 1 long robust setae and 4 slender setae in left and 9 narrow robust setae and 5 slender setae in right. Maxilla 2, inner plate ca. 1.2 times width of outer plate. Maxilliped, inner plate with 3 triangular robust setae distally; outer plate bearing 4 long and 10 short robust setae mediodistally; palp article 3 dorsal surface with 4 thick setae and many fine setae.

Pereon ( Figs 2, 4). Pereonite 7 not projected posterodorsally. Gnathopod 1 short; coxa subrectangular, with a small notch each on anteroventral and posteroventral margins, medial surface bearing 6 setae; basis slender, straight, anterior margin lined with short setae, posterior margin bearing 2 long setae, medial surface with several setae; merus acutely projected distally, with several thick setae on posterodistal margin; carpus relatively long, posterior margin bearing many thick setae; propodus slightly shorter than carpus (ca. 0.9 times), posterior margin weakly sinuate, with several thick setae, palm weakly oblique, defined by 2 (1 lateral and 1 medial) short robust setae; dactylus short. Gnathopod 2 much longer than gnathopod 1; coxa roundish rectangular, with a small notch each on anteroventral and posteroventral margins, medial surface bearing 3 setae; basis slender, straight, anterior margin lined with short setae, posterior margin bearing 1 long and 5 short setae; merus acutely projected distally, posterior margin with a few setae; carpus long and narrow, posterior margin bearing several bundles of slender setae; propodus longer than carpus (ca. 1.1 times), narrow, anterior margin lined with short setae, posterior margin bearing many bundles of slender setae, palm weakly oblique, defined by 2 (1 lateral and 1 medial) short robust setae; dactylus short. Pereopod 3 shorter than gnathopod 2; coxa roundish trapezoidal, with a small notch each on anteroventral and posteroventral margins, medial surface bearing 5 setae; basis slightly curved anteriorly, anterior margin and anterodistal corner each with 3 robust setae, posteroproximal margin with 3 slender setae, posterodistal corner bearing a robust seta; merus anterodistal corner with a robust seta; carpus posterior margin with 2 robust setae; propodus longer than carpus, posterior margin with 4 robust setae; dactylus with a minute projection on inner margin. Pereopod 4 almost same length as pereopod 3; coxa ventral margin slightly angular, with 2 and 5 small notches on anteroventral and posteroventral margins, respectively, medial surface bearing several setae; basis slightly curved anteriorly, anterior margin and anterodistal corner with 1 and 2 robust setae, respectively, posteroproximal margin with 3 slender setae, posterodistal corner bearing a robust seta; ischium–dactylus similar to those of pereopod 3. Pereopod 5 almost same length as pereopod 4; coxa posterior margin with 2 small notches, medial surface with a few setae anteroventrally; basis ovoid, with anterolateral ridge, anterior margin with a proximal seta and 6 robust setae, anterodistal corner bearing 2 robust setae, posterior margin minutely serrated, medial surface with vertical ridge bearing a robust seta; ischium with a robust seta at anterodistal corner; merus with 1+2+2+1 anterior, 3 anterodistal, 2 posterior and 5 posterodistal robust setae; carpus with 1+2+2 anterior, 5 anterodistal, 3 posterior and 5 posterodistal robust setae; propodus with 2+2+2+2 anterior, 2 anterodistal and 2+2+2 posterior robust setae; dactylus with a minute projection. Pereopod 6 about 1.2 times as long as pereopod 5; coxa anterior margin straight, with 4 setae, posteroventral margin with 6 small notches; basis ovoid, with anterolateral ridge, anterior margin with several proximal setae and 4 robust setae, anterodistal corner bearing 3 robust setae, posterior margin minutely serrated, medial surface with vertical ridge bearing a robust seta; ischium with a robust seta at anterodistal corner; merus with 2+2+2 anterior, 3 anterodistal, 4 posterior and 6 posterodistal robust setae; carpus with 2+2+2 anterior, 5 anterodistal, 1+2 posterior and 5 posterodistal robust setae; propodus with 1+2+2+2+2 anterior, 3 anterodistal and 2+2+2 posterior robust setae; dactylus with a minute projection. Pereopod 7 about 1.1 times as long as pereopod 6; coxa short, oval, posteroventral margin with 4 small notches; basis ovoid, with anterolateral ridge, anterior margin with several proximal setae and 5 robust setae, anterodistal corner bearing 2 robust setae, posterior margin minutely serrated, medial surface with short vertical ridge bearing a robust seta; merus with 1+2+3+1 anterior, 3 anterodistal, 3 posterior and 5 posterodistal robust setae; carpus with 1+3+3+2 anterior, 5 anterodistal, 2+1+2 posterior and 6 posterodistal robust setae; propodus with 1+2+2+2+2+2 anterior, 2 anterodistal and 2+2+2 posterior robust setae; dactylus with a minute projection.

Pleon ( Figs 2, 5). Pleonites 1, 2 projected posterodorsally. Epimeral plates 1–3, posteroventral corners minutely produced in plates 1, 3 and strongly produced in plate 2, lateral surfaces with ridge, ventral margins bare. Pleopods, pleopod 2 longest; each peduncle bearing several setae and 2 coupling hooks, peduncle of pleopod 1 with a robust seta posteromedially, peduncle of pleopod 3 bearing 4 posteromedial and 1 lateral robust setae; outer rami longer than inner rami, both rami with 12–13 articles (11 articles in outer ramus of pleopod 1 owing to regeneration). Uropod 1, peduncle long, dorsal surface with 6 lateral, 1 laterodistal, 4 medial and 1 mediodistal robust setae, ventrodistal end slightly produced; outer ramus ca. 0.65 times length of peduncle, with 4 lateral and 4 terminal robust setae; inner ramus ca.1.4 times as long as outer ramus, with 5 lateral, 4 (1 lost) medial and 4 terminal robust setae. Uropod 2 about 0.85 times as long as uropod 1; peduncle short, with 3 lateral, 1 laterodistal and 1 mediodistal robust setae, ventrodistal end slightly produced; outer ramus ca. 0.7 times length of peduncle, with 2 lateral and 4 (1 lost) terminal robust setae; inner ramus about twice as long as outer ramus, with 4 lateral, 4 medial and 4 terminal robust setae. Uropod 3 about 0.8 times length of uropod 2; peduncle very short, longer than wide, ventrodistal end slightly produced, lateral margin with 2 short setae; outer ramus ca. 1.6 times length of peduncle, with 4 lateral and 4 medial robust setae; inner ramus about 1.55 times as long as outer ramus, with 9 lateral and 11 medial robust setae. Telson small, trapezoidal, distal margin truncated, dorsal surface with 6 sensory setae, lateral margins bearing a few minute setae.

Description of male. Based on paratype, male, 4.4 mm (OMNH-Ar-13207). Almost similar to holotype, ovigerous female, 4.9 mm (OMNH-Ar-13204) except for oostegites. Gnathopods resembling those of female; but gnathopod 1 basis with inner long seta and propodus slightly shorter than carpus (ca. 0.95 times, Fig. 5 M-G1), and gnathopod 2 basis lacking posterior long seta ( Fig. 5 M-G2).

Coloration in life. Based on paratype, female, 4.2 mm (OMNH-Ar-13210, Fig. 6). Head faintly-orangish white, eyes bright red; pereonites, pleonites and coxae orangish white with orange margins; antennae orangish white; gnathopods and pereopods white except for orange bases of pereopods 5–7; pleopods and uropods white.

Remarks. Lobatoradarea littoralis sp. nov. is characterized by the strongly produced posteroventral corner of the epimeral plate 2. This character is shared with L. kagoshimensis sp. nov. in the other Lobatoradarea species; however, this new species can be distinguished from L. kagoshimensis by the slightly projected anteroventral corner of the head and the small eyes.

Habitat. Under stones or in coarse sand in the shallow subtidal zone ( 0–2 m depth).

Distribution. Japan: from Tagurasaki in Wakayama Prefecture to Toyokunizaki in Osaka Prefecture (present study).