Ligia laticarpa, 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 : 472-478

Ligia laticarpa sp. nov.

[Japanese name: Aohoshi-funamushi, new]

( Figs 13–17 )

Ligia exotica .— Nunomura, 1975: 34 (?in part).— Nunomura, 1983: 25, fig. 1 (in part).—? Chen, 1987: 9, fig. 1.— Yamanishi, 2011: 2, pls I, II.—?Yin et al ,, 2013: 363, fig. 2V, VII.— Nunomura & Shimomura, 2017a: 509, fig. 289 (in part).

Ligia exotica natural-coastal form Yamanishi, 2021: 167, figs 2, 3.

Material examined. Holotype: male, 38 mm (OMNH-Ar-12571), Toyokunizaki coast, Misaki Town , Osaka Prefecture, 34°19'22"N, 135°06'59"E ( Fig. 1A ), 1 June 2022, coll. H. Ariyama. Paratypes: 2 males, 38, 33 mm (OMNH-Ar-12572, 12573), 1 ovigerous female, 32 mm (OMNH-Ar-12574), 5 males, 35, 33, 33, 29, 28 mm (OMNH-Ar-12575–12577*, 12578, 12579), and 5 ovigerous females, 34, 32, 27, 27, 27 mm (OMNH-Ar-12580– 12584*), same data as holotype. Asterisks indicate specimens for molecular analysis .

Type locality: Toyokunizaki coast in Misaki Town, Osaka Prefecture, Japan .

Etymology: From the Latin latus (= broad) + the Greek carpus, referring to the wide carpus of the male pereopod 1.

Description of male: Based on holotype (OMNH-Ar-12571, 38 mm) and paratype (OMNH-Ar-12572, 38 mm) only for right mandible and lower lip.

Body ( Figs 13A , 16 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 wider than long; distal margin with indistinct median tooth, pair of small intermediate tooth and pair of triangular lateral tooth.

Head ( Figs 13A , 14 ) relatively narrow, about half of body width; eyes situated anterolaterally, diameter ca. 0.4 times of head width. Antennula 3.3% of BL; article 1 wide, with 3 minute setae at ventrodistal corner and 1 short seta on ventral margin; article 2 slender, ventral margin with 5 setae, distal part of dorsal margin bearing many minute setae, ventrodistal corner with 3 setae, mediodistal margin with 4 short aesthetascs; article 3 small, tip rounded. Antenna longer than body (about 1.1 times), tip exceeding pereonite 7; peduncular articles 3–5 with length ratio of 1:2.45:3.35, laterodistal corners of articles 3–5 each bearing small robust seta; flagellum with 34 articles (38 articles in right). Upper lip large and wide, separated into two parts by asymmetrical suture; lower part 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 minute 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 partly coalesced, distal end of basis and palp articles 1–4 with several robust setae; endite reaching palp article 2, with ca. 50 denticles and dense fine setae.

Pereon ( Fig. 15 ). Pereopod 1 short; basis parallel-sided; ischium widened distally, about 2/3 length of basis, laterodistal corner bearing 2 long robust setae; merus and carpus wide, almost same length as ischium, ventral margins weakly and strongly swollen, respectively; propodus narrow, anterodistal end with distinct projection; 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 2 long robust setae; merus shorter than ischium, ventral margin weakly swollen; carpus long and broad, about 1.7 times length of merus, ventral margin swollen; propodus narrow, proximal part strongly curved, ventral margin without robust setae; dactylus short. Pereopod 4 slightly 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 1.35 times length of merus, ventral margin not swollen; propodus straight and narrow, same length 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. 1.4–1.6 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. 16 ). Penile papillae simple, narrowed distally, lateral margins bearing fine setae. Pleopod 1 with reniform exopod, endopod roundly projected mediodistally, medial and posterior margins setose. Pleopod 2, protopod with oblong outer branch; exopod oval, attached ventrally on protopod, anterior–medial–posterior margins weakly setose; endopod slender, lengthened posteriorly, article 2 about 1.75 times length of exopod; appendix masculina with minutely spinous swelling on lateral surface and rounded projection on dorsolareral (left) or dorsomedial (right) surface, distal margin appearing bilobed. Uropod very long, about 0.7 times of BL; peduncle slender, medial margin bearing 11 robust setae, distal margin with lateral projection and a medial robust seta; inner ramus very slender, ca. 1.8 times as long as peduncle, tip with slightly curved second article; outer ramus also slender, tip lost.

Description of female [based on paratype (OMNH-Ar-12574, 32 mm); Figs 13B , 17 ]: Body wider than that of male, width 47% of length; sutures fully present on pereonites 2–4, partly present on pereonites 1, 5. Antenna longer than body (about 1.1 times), flagellum with 35 articles in left and 36 articles in right. Pereopod 1, basis parallel-sided; ischium widened distally, ca. 0.65 times length of basis, laterodistal corner bearing 2 long robust setae; merus longer than ischium, weakly widened distally, ventral margin slightly swollen; carpus shorter than merus, relatively wide, 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 0.85–0.9 times length of merus, ventral margin not swollen; propodus slender, proximal part not curved; dactylus short. Pleopod 2, exopod oval, with margins bearing dense setae; endopod small, roundly projected mediodistally. Uropod about 0.6 times of BL. Other parts almost similar to those of male except for penile papillae and oostegites.

Variation: Pleotelson ( Fig. 16M 1 -Pt), dorsal margin with distinct median tooth. Antenna ca. 1.0–1.1 times of BL, flagellum with 33–41 articles. Male pereopod 1, ventral margin of carpus weakly swollen in most individuals. Male pleopod 2, appendix masculina ( Fig. 16M 2 -AM, M3-AM) with a rounded projection always on dorsomedial surface. Uropod with variable length (about 0.4–0.8 times of BL), tip of outer ramus lost in all individuals.

Coloration in life ( Fig. 13 ). Male: antenna light brown, eyes black; body and uropod orangish light brown, but median part of body dark brown, scattered with many blue spots. Female: antenna light brown, eyes black; body and uropod light brown, but median part of body brown, with several light brown marks and many indistinct light brown spots.

Diagnostic molecular characters (16S rRNA): A distinguishing nucleotide position for Ligia laticarpa sp. nov is found at position 63, where the nucleotide is G, contrasting with A in the other species.

Remarks: Ligia laticarpa sp. nov. is very similar to L. furcata sp. nov. in many characters (e.g., number of articles in the antenna flagellum and shapes of the pereopods 2, 3 in both sexes). However, L. laticarpa can be distinguished from L. furcata in (1) the male pereopod 1 with strongly or weakly swollen carpus, and with notfurcate projection of propodus, (2) the appendix masculina with a rounded projection on dorsomedial surface (only left appendix masculina of the holotype has a dorsolateral projection, probably owing to twisting), and (3) the female pereopod 1 with weakly widened merus. This new species also resembles Ligia exotica ; however, both L. laticarpa and L. furcata differ from L. exotica in (1) the right lacinia mobilis with a large triangular projection and several small rounded projections, (2) the appendix masculina with projection, and (3) the slender carpus of the female pereopods 2, 3. In Ligia laticarpa , the dorsal margin of the pleotelson varies and the tip of the uropod outer ramus is always lost. These states are estimated to be caused by friction. The blue spots on the dorsal surface of the adult male are unique among the species examined.

The morphological characters of this new species quite agree with those of Ligia exotica sensu Yamanishi (2011) and “ L. exotica natural-coastal form” in Yamanishi (2021). In the foreign L. exotica species complex, specimens from China have a relatively similar appendix masculina ( Chen 1987; Yin et. al. 2013). Although they are possibly this new species, detailed morphological comparison in addition to the appendix masculina is needed for precise identification.

Habitat: Supralittoral, on rocks.

Distribution. Japan: Hannan City in Osaka Prefecture to Wakayama City in Wakayama Prefecture, and Sumoto City in Hyogo Prefecture ( Yamanishi 2021; present study).? China ( Chen 1987; Yin et al. 2013).

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 2. Maximum likelihood phylogenetic tree based on 16S rRNA nucleotide sequences of Ligia species. Ligia hawaiensis and L. perkinsi were used as the outgroups. Values at nodes represent bootstrap values/Bayesian posterior probabilities. Vertical bars represent assignments by species delimitation analyses, including ASAP, bPTP and mPTP. The scale bar represents the number of nucleotide substitutions per site. The complete list of used nucleotide sequences is shown in Table S1. The detailed phylogenetic tree is shown in Fig. S2.

FIGURE 13. Ligia laticarpa sp. nov. A, holotype, male, 38 mm (OMNH-Ar-12571); B, paratype, ovigerous female, 32 mm (OMNH-Ar-12581). Scales: 10 mm.

FIGURE 14. Ligia laticarpa sp. nov. Holotype, male, 38 mm (OMNH-Ar-12571) and paratype, male, 38 mm (OMNH-Ar- 12572) [M]. Scales: 0.5 mm.

FIGURE 15. Ligia laticarpa sp. nov. Holotype, male, 38 mm (OMNH-Ar-12571). Posterior views (posterolateral to posteromedial). Scales: 1 mm.

FIGURE 16. Ligia laticarpa sp. nov. Holotype, male, 38 mm (OMNH-Ar-12571); paratype, male, 38 mm (OMNH-Ar-12572) [M1]; paratype, male, 33 mm (OMNH-Ar-12576) [M2]; and paratype, male, 28 mm (OMNH-Ar-12579) [M3]. Protopod lost in medial part of Pl4. Scales: 0.5 mm.

FIGURE 17. Ligia laticarpa sp. nov. Paratype, ovigerous female, 32 mm (OMNH-Ar-12574). Scales: 1 mm.