Ligia furcata, Ariyama & Hiki, 2024

Ariyama, Hiroyuki & Hiki, Kyoshiro, 2024, A morphological and molecular study of Ligia exotica Roux, 1828 (Crustacea: Isopoda: Ligiidae) from Japan, with descriptions of two new species, Zootaxa 5453 (4), pp. 451-486 : 466-472

Ligia furcata sp. nov.

[Japanese name: Futamata-funamushi, new]

( Figs 8–12 )

Ligia exotica .—? Richardson, 1904: 49.—? Kato, 1936: 333, figs 1–3.— Nunomura, 1983: 25, fig. 1 (in part).—? Khalaji-Pirbalouty & Wägele, 2010: 144, fig. 18f. — Nunomura & Shimomura, 2017a: 509, fig. 289 (in part).

Ligyda exotica .— Richardson, 1905: 676, fig. 716 (in part).—? Richardson, 1909: 125.—? Goto & Terao, 1911: 270, figs 1–15.

Material examined. Holotype: male, 36 mm (OMNH-Ar-12599), Chigogafuchi, Enoshima Island, Fujisawa City , Kanagawa Prefecture, 35°17'57"N, 139°28'28"E ( Fig. 1C ), 16 June 2022, coll. H. Ariyama. Paratypes: 1 male, 34 mm (OMNH-Ar-12600), 1 female, 32 mm (OMNH-Ar-12601), 1 female with juveniles, 26 mm (OMNH-Ar-12602), 2 females with juveniles, 33, 30 mm (OMNH-Ar-12603*, 12605*), and 3 females, 32, 28, 26 mm (OMNHAr-12604*, 12606*, 12607*), same data as holotype. Asterisks indicate specimens for molecular analysis .

Type locality: Chigogafuchi in Enoshima Island , Fujisawa City, Kanagawa Prefecture, Japan .

Etymology: From the Latin furcatus, - a, - um (=furcate), referring to the shape of the male pereopod 1 propodus.

Description of male: Based on holotype (OMNH-Ar-12599, 36 mm) and paratype (OMNH-Ar-12600, 34 mm) only for whole body and tip of uropod.

Body ( Figs 8A , 11 Pt) oblong oval, width 43% of length; dorsal surface granular. Pereonites 1–7 gradually shorter, sutures indistinct; anterolateral corner of pereonite 1 produced triangularly, lateral margins of pereonites 1–7 projected posteriorly, with angle progressively sharpened. Pleonites 1 and 2 short and narrow; pleonites 3–5 gradually shorter, posterolateral corners of pleonites 3–5 acutely produced. Pleotelson much broader than long; distal margin with indistinct median tooth, pair of intermediate tooth and pair of triangular lateral tooth.

Head ( Figs 8A , 9 ) relatively narrow, about half of body width; eyes situated anterolaterally, diameter ca. 0.4 times of head width. Antennula 3.7% of BL; article 1 wide, with 3 minute setae at ventrodistal corner; article 2 slender, ventral margin with 5 setae, dorsal margin lined with minute setae, ventrodistal corner lacking setae, mediodistal margin bearing 4 short aesthetascs; article 3 small, tip rounded. Antenna longer than body (ca. 1.1 times), but tip not exceeding pereonite 7; peduncular articles 3–5 with length ratio of 1:2.5:3.65, laterodistal corners of articles 4, 5 each bearing small robust seta; flagellum with 35 articles. Upper lip large and broad, separated into two parts by asymmetrical suture; lower part covered with fine setae. Mandibles stout, both incisors and left lacinia mobilis each with 3 rounded cusps, right lacinia mobilis with a large triangular projection and several small rounded projections; setal rows composed of ca. 30 long thick setae; molar large, bearing dense fine setae. Lower lip fleshy, with triangular median lobe; several parts covered with dense fine setae. Maxillura flattened; outer plate apically with 5 thick and 8 slender robust setae and a slender pectinate seta; inner plate bearing 3 large plumose setae mediodistally. Maxilla relatively slender; outer plate wide, rounded distally, covered with dense fine setae; inner plate small. Maxilliped stout; epipod rounded, lateral and distal margins setose; palp partly coalesced with basis, articles 1–2 and articles 4–5 separated, but articles 2–3 and articles 3–4 slightly coalesced, distal end of basis and palp articles 1–4 with several robust setae; endite reaching palp article 2, with ca. 25 denticles and dense fine setae.

Pereon ( Fig. 10 ). Pereopod 1 short; basis parallel-sided; ischium widened distally, about 0.7 times length of basis, laterodistal corner bearing a long robust seta; merus wide, almost same length as ischium, ventral margin weakly swollen; carpus shorter than merus, narrow, ventral margin slightly swollen; propodus narrow, anterodistal end furcate, with rounded and semitriangular projections; dactylus short. Pereopods 2, 3 similar in shape each other, longer than pereopod 1; basis slightly widened distally; ischium widened distally, ca. 0.6 times length of basis, laterodistal corner with a long robust seta; merus shorter than ischium, ventral margin weakly swollen; carpus long and broad, about 1.3 times length of merus, ventral margin swollen; propodus narrow, proximal part strongly curved, ventral margin without robust setae; dactylus short. Pereopod 4 longer than pereopod 3; basis weakly widened distally, ischium widened distally, ca. 0.6 times as long as basis, laterodistal corner with a long robust seta; merus almost same length as ischium, ventral margin not swollen; carpus slender, about 1.25 times length of merus, ventral margin not swollen; propodus straight and narrow, about 1.1 times as long as carpus; dactylus short. Pereopods 5–7 similar in shape one another, longer than pereopod 4, pereopods 6, 7 almost same length, longer than pereopod 5; basis expanded at distal 1/5 point of lateral margin; ischium widened distally, ca. 0.7–0.8 times length of basis, laterodistal corner with a long robust seta; merus shorter than ischium, ventral margin slightly excavated; carpus slender, ca. 1.3–1.4 times length of merus, ventral margin not swollen; propodus straight and narrow, about 1.2 times length of carpus; dactylus short, with a strap-like seta in pereopods 6, 7.

Pleon ( Fig. 11 ). Penile papillae simple, narrowed distally, lateral margins bearing fine setae. Pleopod 1 with reniform exopod, endopod roundly projected posteromedially, medial and posterior margins weakly setose. Pleopod 2, protopod with oblong outer branch; exopod oval, attached ventrally on protopod, anterior and lateral margins strongly setose, posterior margin weakly setose; endopod slender, lengthened posteriorly, article 2 about 1.65 times length of exopod; appendix masculina with minutely spinous swelling on lateral surface and angular (left) or rounded (right) projection on dorsolateral surface, distal margin slightly projected. Pleopods 3–5 similar in shape one another; protopod bilobed, outer lobe long, inner lobe short, heavily setose medially and posteriorly; exopod wide, attached dorsally on protopod, posteromedial corner weekly projected, medial margin heavily setose, posterior margin weakly setose; endopod also wide (narrow in pleopod 4 probably due to regeneration), semiquadrate. Uropod very long (ca. 0.8 times of BL); peduncle slender, medial margin bearing 8 robust setae, distal margin with lateral projection and a medial robust seta; both rami very slender, over 1.7 times as long as peduncle, tip of inner ramus with slightly curved second article, tip of outer ramus lost.

Description of female [based on paratype (OMNH-Ar-12605, 30 mm) for whole body and paratype (OMNHAr-12601, 32 mm) for others; Figs 8B , 12 ]: Body wider than that of male, width 47% of length; sutures fully present on pereonites 2–4, partly present on pereonites 1, 5–7. Antenna shorter than body (ca. 0.9 times), flagellum with 34 articles in left and 31 articles in right. Pereopod 1, basis parallel-sided; ischium widened distally, about 0.65 times length of basis, laterodistal corner bearing a long robust seta; merus longer than ischium, straight, ventral margin not swollen; carpus narrow, shorter than merus, ventral margin not swollen; propodus slender, anterodistal end lacking projection; dactylus short. Pereopods 2, 3 similar in shape each other, longer than pereopod 1; basis slightly widened distally; ischium widened distally, ca. 0.55 times length of basis, laterodistal corner with a long robust seta; merus longer than ischium, ventral margin straight; carpus short and narrow, about 0.9 times length of merus, ventral margin not swollen; propodus slender, proximal part not curved; dactylus short. Pleopod 2, exopod oval, anterior–medial margins heavily setose, posterior margin weakly setose; endopod small, roundly projected posteromedially. Other parts almost similar to those of male except for penile papillae and oostegites.

Variation: Antenna ca. 0.9–1.1 times of BL, flagellum with 31–39 articles. Male pleopod 2, appendix masculina ( Fig. 11 M-R-AM) similar to left appendix masculina of holotype, but angle of projection acuter. Uropod ca. 0.5–0.8 times of BL, tip of outer ramus lost in all individuals.

Coloration in life ( Fig. 8 ). Male: antenna light brown, eyes black; body and uropod orangish light brown, but median part of body dark brown, scattered with several gray spots. Female: antenna light brown, eyes black; body light brown, but median part brown, with several light brown marks and several gray spots; uropod brown.

Diagnostic molecular characters (16S rRNA): Distinguishing nucleotide positions for Ligia furcata sp. nov. are found at positions 251, 270, and 481, where the nucleotides are C, A, and A, respectively, contrasting with A, T, and G in the other species.

Remarks: Ligia furcata sp. nov. has the long antenna and uropod and the male pereopod 1 with a distal projection on the propodus, which are common characters of the Ligia exotica species complex. This species also has the furcate propodus of the male pereopod 1 and the appendix masculina with an angular projection on the dorsolateral surface. These characters are different from the true L. exotica . In addition, the female of the new species has a narrow carpus of the pereopods 2, 3, whereas the female of L. exotica has a broad carpus.

Goto & Terao (1911) examined Ligia exotica specimens collected from Chiba – Kanagawa Prefectures near the type locality of this new species. They showed a figure of the appendix masculina resembling the right appendix masculina of the holotype ( Fig. 11 R-AM). Kato (1936) examined L. exotica from probably near the type locality (his laboratory was situated in Susaki, Shizuoka Prefecture), and showed male and female pereopods 1–4 like L. furcata . These facts suggest that these specimens may be this species. Khalaji-Pirbalouty & Wägele (2010) also examined a Japanese specimen (collected site unknown) and showed a photograph of the male pereopod 1 with a distally furcate propodus. This is possibly L. furcata .

Habitat: Supralittoral, on rocks.

Distribution. Japan: Enoshima Island in Kanagawa Prefecture (present study);? Chiba, Tokyo and Kanagawa Prefectures ( Goto & Terao 1911).

Figures

FIGURE 1. Map showing collecting sites of the examined specimens. A, Misaki Town in Osaka Prefecture; B, Nishinomiya City in Hyogo Prefecture; C, Enoshima Island in Kanagawa Prefecture; D, Lake Shinji in Shimane Prefecture.

FIGURE 8. Ligia furcata sp. nov. A, paratype, male, 34 mm (OMNH-Ar-12600); B, paratype, female, 30 mm (OMNH-Ar- 12605). Scales: 10 mm.

FIGURE 9. Ligia furcata sp. nov. Holotype, male, 36 mm (OMNH-Ar-12599). Scales: 0.5 mm.

FIGURE10.Ligiafurcata sp. nov. Holotype,male,36 mm (OMNH-Ar-12599).Posteriorviews (posterolateraltoposteromedial). Scales: 1 mm.

FIGURE 11. Ligia furcata sp. nov. Holotype, male, 36 mm (OMNH-Ar-12599) and paratype, male, 34 mm (OMNH-Ar-12600) [M]. Scales: 1 mm.

FIGURE 12. Ligia furcata sp. nov. Paratype, female, 32 mm (OMNH-Ar-12601). Scales: 1 mm.