Platorchestia paludosus, Cheng, Yu-Ting, Nakazono, Kenji, Lin, Kirk & Chan, Benny K. K., 2011

Cheng, Yu-Ting, Nakazono, Kenji, Lin, Kirk & Chan, Benny K. K., 2011, Cryptic diversity of the semi-terrestrial amphipod Platorchestia japonica (Tattersall, 1922) (Amphipoda: Talitrida: Talitridae) in Japan and Taiwan, with description of a new species, Zootaxa 2787, pp. 1-18 : 4-16

Platorchestia paludosus sp. nov.

(Figures 2–9)

Platorchestia japonica . ― Miyamoto & Morino 2004: 83 –88 (non P. japonica ).

Materials examined. Holotype (NMNS—6519-001) 1 male, Guan-du, Taipei County, Taiwan, Aug 2008, Coll. Y- T. Cheng. Paratypes (NMNS—6519-002–06519-009) 4 males and 4 females, data same as holotype. Paratypes (AM—P.84807) 2 males and 2 females, data same as holotype. Paratypes (ASIZCR—000230) 2 males and 2 females, data same as holotype.

Comparative material. Platorchestia japonica ( Tattersall, 1922) . Lake Biwa, Japan. 2 males 2 females.

Description. Male. Body smooth, without protuberance. Eyes sub-rounded, larger than 1/3 of head height. Antenna 1 ( Figs 3 –a, b, c and d) short with 6–7 articles (3 peduncle articles, 3–4 flagellated articles), slightly longer than article 4 of antenna 2, peduncle articles 1–3 equal in length, dorsal side convex, ventral side flattened, each peduncle article with simple setae, article 4 slightly curved, each flagellated article with 2 groups of simple setae type IV ( Fig. 1 –d) on the inner and outer side of the dorsal surface.

Antenna 2 ( Figs 3 –e, f, and g) up to 1/3 of the body length, outer margin of ventral side of peduncle article 3 with 3–5 simple setae type IV ( Fig. 1 –d), a medial furrow extend from distal 1/3 of peduncle article 4 to entire peduncle article 5, length of article 5 equals to combined length of article 3 and 4, 11–14 flagellated articles each with medial furrow, flagellum subequal to peduncle 3–5 combined in length; tip of antenna 2 with simple setae type V ( Fig. 1 –e).

Upper lip entire, apical margin with fine setule.

Incisor of mandible ( Figs 3 –i, j) 5 to 6 dentate, left lacinia mobilis 5–dentate, right lacinia mobilis bi-fid, with serrated cutting edges; molar finely serrated, right molar convex, left molar concave; 3–4 pappose setae type I ( Fig. 1 –p) located in the region between the lacinia mobilis and molar, 1 pappose seta type II ( Fig. 1 –q) on the dorsal side of molar.

Lower lip bi-lobed, lobes wide, with fine setule on the inner margin.

Inner plate of maxilla 1 ( Figs 3 –l, m) narrow, with 2 apical papposerrate setae type I ( Fig. 1 –r); outer plate with 9 serrate setae type I ( Fig. 1 –j), with a row of 13–19 setule type I ( Fig. 1 –t) on ventral base of inner 4 serrate setae; palp very small, 2 articulate.

Inner plate of maxilla 2 ( Fig. 3 –n, o, p, q, r and s) smaller than outer plate, distal margin with 17–19 simple setae type III ( Fig. 1 –c), a row of 8–10 serrate setae type II ( Fig. 1 –k) on ventral and a row of 6–11 serrate setae type IV ( Fig. 1 –m) on dorsal, inner margin with 2 papposerrate setae type I ( Fig. 1 –r), inner one longer; distal margin of outer plate with 15–20 simple setae type III ( Fig. 1 –c), a row of 9–12 serrate setae type II ( Fig. 1 –k) on ventral surface, a row of 3 serrate setae type IV ( Fig. 1 –m) and 2 serrulate setae type I ( Fig. 1 –n) on dorsal surface.

FIGURE. 2. Platorchestia paludosus sp. nov. a. external view, male. b. female gnathopod 1. c. female gnathopod 2.

Distal end of maxilliped inner plate ( Figs 4 –b, e) with 3 cuspidate setae type I ( Fig. 1 –g), a row of 3–4 papposerrate setae type II ( Fig. 1 –s) behind the cuspidate setae, dorsal surface ( Fig. 4 –b) with a row of papposerrate setae type II ( Fig. 1 –s) along inner margin, with fine setae situating behind the papposerrate setae; ventral surface ( Fig. 4 –e) with several papposerrate setae type II ( Fig. 1 –s); distal end of outer plate ( Figs 4 –n, o) with a row of 4–5 papposerrate setae type II ( Fig. 1 –s) along margin, along inner margin to ventral surface of distal corner with 2 rows of simple setae type VI ( Fig. 1 –f), ventral surface of medial inner margin ( Fig. 4 –q) with a row of 3–5 simple setae type VI ( Fig. 1 –f); palp article 1 wider than high, with a row of 3–4 simple setae type VI ( Fig. 1 –f) on ventral surface of distal inner corner ( Fig. 4 –a, m), distal outer margin ( Figs 4 –a, c, j and l) with 1–2 cuspidate setae type III ( Fig. 1 –i) and 2–3 simple setae type VI ( Fig. 1 –f); distal inner corner of ventral surface of palp article 2 ( Figs 4 –a, and h) with a row of 3–4 simple setae type VI ( Fig. 1 –f), along the inner margin ( Figs 4 –a, and k) with 2 rows of simple setae VI ( Fig. 1 –f), distal outer margin ( Figs 4 –a, c, g and i) with 1–2 cuspidate setae type III ( Figs 1 –i) and 2–3 simple setae type VI ( Fig. 1 –f), article 3 rounded apically, dorsal surface ( Figs 4 –c, and f) with a row of 4–5 serrate setae type III ( Fig. 1 –l) and 2–3 simple setae type VI ( Fig. 1 –f) along the base of palp article 4, ventral surface with ( Figs 4 –a, d) several simple setae type VI ( Fig. 1 –f), outer distal corner ( Fig. 4 –a, c, d and f) with a group of 2–3 simple setae type IV ( Fig. 1 –d); article 4 small with several simple setae type III ( Fig. 1 –c) and simple setae type VI ( Fig. 1 –f) apically.

Gnathopod 1 ( Figs 5 –a, and b) coxa with straight or convex anterior margin, ventral margin convex with a few setae; basis slightly expanded posterodistally, subequal with merus and carpus when combined in length; ischium shortest, anteroproximal margin with a notch; merus sub-triangular, rounded posteriorly; carpus ( Figs 5 –c, and d) with scabrous tumescent protuberance posterodistally, outer lateral surface ( Figs 5 –c) with a row of 2–3 serrate setae type III ( Fig. 1 –l) and 2–3 cuspidate setae type III ( Fig. 1 –o) at base of tumescent protuberance, inner lateral surface ( Fig. 5 –d) with 7–10 serrate setae type III ( Fig. 1 –l) without cuspidate setae; propodus ( Figs 5 –e, f) with scabrous tumescent protuberance posterodistally, outer lateral surface with a row of 4–6 serrate setae type III ( Fig. 1 –l) along posteroproximal margin to medial base of tumescent protuberance, outer lateral surface with a group of 4–5 simple setae type IV ( Fig. 1 –d) on protuberance base distal end, dactylus base with a group of 2–3 simple setae type IV ( Fig. 1 –d), anterodistal corner with a group of 2–3 simple setae type IV ( Fig. 1 –d); length of dactylus subequal to palm, and not reach posterodistal angle of propodus.

Gnathopod 2 ( Figs 5 –g, h) coxa as wide as deep with posterior process, ventral margin convex, basis anterior margin straight, posterior margin convex and proximal end necked; ischium larger than merus, with a notch on proximal end of anterior margin; length of merus subequal to carpus, with convex posterior margin; carpus with convex anterior margin; propodus oval, palm margin curved, without notch, both lateral surface with a row of cuspidate setae type III ( Fig. 1 –i); dactylus curved, as long as palm.

Pereopods 3–7 cuspidactylate. Pereopod 3 coxa ( Fig. 6 –a) subquadrate with posterior process, ventral margin slightly convex; basis longest, subequal to combined length of merus and carpus; ischium shortest, anteroproximal margin notched; merus longer than carpus, anterior margin slightly convex, posterior margin straight; carpus anterior and posterior margins parallel; propodus slender, longer than carpus, slightly shorter than merus; dactylus ( Fig. 6 –c) subequal to ischium in length, posterior nail base with 1 simple setae type I ( Fig. 1 –a).

Pereopod 4 ( Figs 6 –d, and e) similar to pereopod 3, shorter, coxa ( Fig. 6 –d) subquadrate, with posterior process, ventral margin straight; basis longest, subequal to combined length of merus and carpus, slightly convex; ischium shortest, anteroproximal margin notched; merus longer than carpus, anterior margin slightly convex, posterior margin straight; carpus shorter than that of pereopod 3, both margins parallel; propodus slender, subequal to merus, dactylus ( Fig. 6 –f) pinched, posterior nail base with 1 simple seta type I ( Fig. 1 –a).

Pereopod 5 coxa ( Fig. 6 –g) bilobed, anterior lobe larger than posterior lobe; basis oval; ischium shortest, posteroproximal margin notched; merus subequal to carpus in length, anterior margin straight, posterior margin slightly convex; carpus both margins parallel; propodus slender; dactylus ( Fig. 6 –i) with 1 simple seta type I ( Fig. 1 –a) on anterior nail base.

Pereopod 6 coxa ( Fig. 6 –j) bilobed, anterior lobe very small, anterior margin of posterior lobe nearly vertical, anterodistal corner strongly curved; basis oval; ischium shortest, posteroproximal margin notched; merus subequal to carpus in length, anterior margin straight, posterior margin slightly convex; carpus both margins parallel; propodus slender, longest; dactylus ( Fig. 6 –l) with 1 simple seta type I ( Fig. 1 –a) on anterior nail base.

Pereopod 7 coxa ( Fig. 6 –m) rounded posterodistally; basis oval, posterodistal lobe broader than pereopod 5–6; ischium shortest, posteroproximal margin notched; merus subequal to carpus, anterior margin straight, posterior margin slightly convex; carpus anterior and posterior margins parallel; propodus slender, longest; dactylus ( Fig. 6 – o) with 1 simple seta type I ( Fig. 1 –a) on anterior nail base.

Pleopods ( Figs 7 –a, b, c, d, e and f) biramous, peduncle and ramus subequal in length, pleopod 3 peduncle shortest, ramus with 7–10 articulated segments.

Peduncle of uropod 1 ( Figs 7 –g, h) slightly longer than ramus, with 1 row of 4–5 cuspidate setae type III ( Fig. 1 –i) along each dorsal lateral margin; outer ramus with 3–5 cuspidate setae type II ( Fig. 1 –h) on distal end, without seta on medial region; inner ramus with 3–5 cuspidate setae type II ( Fig. 1 –h) on distal end, a row of 3–4 cuspidate setae type III ( Fig. 1 –i) along dorsal margin, without 1–2 cuspidate setae type III ( Fig. 1 –i) along outer lateral region.

Peduncle of uropod 2 ( Figs 7 –i, j) subequal to ramus in length, with 3 cuspidate setae type III ( Fig. 1 –i) on dorsal region; outer ramus with 3 cuspidate setae type II ( Fig. 1 –h) on distal end, with 1 cuspidate seta type III ( Fig. 1 – i) on medial region; inner ramus with 5 cuspidate setae type II ( Fig. 1 –h) on distal end, 2–3 cuspidate setae type III ( Fig. 1 –i) on dorsal margin, with 1–2 cuspidate setae type III ( Fig. 1 –i) on outer lateral region.

Uropod 3 ( Figs 7 –k, l), 1– 2 cuspidate setae type III ( Fig. 1 –i) on peduncle medial region, ramus with a group of 3 simple setae type I ( Fig. 1 –a) on distal end, 0–1 simple setae type I ( Fig. 1 –a) on medial region.

Telson ( Figs 7 –m) bilobed, longer than wide, with a group of 3–4 cuspidate setae type III ( Fig. 1 –i) on distal end, 1–2 cuspidate setae type III ( Fig. 1 –i) as a group on dorsal lateral margin.

Female. Antenna 1 short, slightly beyond article 4 of antenna 2, with 6–7 articles (3 peduncle articles, 3–4 flagellated articles), peduncle articles 1–3 equal in length, article 4 slightly curved, each flagellated article with two groups of simple setae on the inner and outer side of dorsal surface.

Antenna 2 up to 1/3 of body length. Outer margin of ventral side of article 3 with 3–5 simple setae, a medial furrow extending from distal 1/3 of article 4 to the entire article 5, length of article 5 equals to total of article 3 and 4, 12–14 flagellated articles, each with medial furrow. Tip of antenna 2 with a group of simple setae.

Coxa of gnathopod 1 ( Figs 8 –a, f) anterior margin straight or convex, ventral margin convex; basis straight; carpus without tumescent protuberance, posterior margin with 2 long and 4–6 short cuspidate setae type III ( Fig. 1 – i); propodus ( Figs 8 –b, g) without tumescent protuberance, inner lateral surface medial region with 4–5 serrate setae type III ( Fig. 1 –l), outer lateral surface medial region with a row of 2–3 cuspidate setae type III ( Fig. 1 –i) along margin, posterior margin with 2 rows of cuspidate setae type III ( Fig. 1 –i), outer lateral surface with a group of 3–4 simple setae type IV ( Fig. 1 –d) on dactylus base, 3–4 simple setae type IV ( Fig. 1 –d) on posterodistal corner, anterodistal corner with 3–6 simple setae type IV ( Fig. 1 –d); dactylus longer than width of propodus.

Gnathopod 2 ( Figs 8 –c, h) coxa as wide as deep with posterior process, convex ventral margin, basis expanded anteroproximally, posterior margin straight; ischium subequal to merus in length; merus ( Figs 8 –d, i) with small scabrous region posterodistally; carpus with scabrous tumescent protuberance posterodistally; propodus ( Figs 8 –e, j) with posterodistal tumescent protuberance elongated distally, scabrous region from posteroproximal end to posterodistal end, outer lateral surface with 10–14 serrate setae type III ( Fig. 1 –l) along scabrous region, inner lateral surface with 16–19 serrate setae type III ( Fig. 1 –l) along scabrous region, palm margin short, and outer lateral palm margin with a row of 4–5 simple setae type I ( Fig. 1 –a), anterodistal corner with 6–8 simple setae type I ( Fig. 1 –a); dactylus curved as long as palm.

Habitat. This salt marsh in Guan-du, Taiwan is dominated by Phragmites communis (L.) Trin. and Brachiaria mutica (Forsk) Stapf. , with irregular flooding after raining. Platorchestia paludosus sp. nov. was found under leaflitter of Brachiaria mutica (Forsk) on the water front of estuarine marshes.

Etymology. The word ‘paludosus’ indicates that the species is common in marshy habitats.

Molecular analysis. We got 618 b.p. aligned sequence of COI (GC ratio: 0.359), from 43 samples of P. paludosus sp. nov. and four samples of P. japonica . The number of total polymorphic sites was 102 within which 75 were parsimony informative sites (PIS), defining 13 haplotypes. There were 9 (3 PIS) and 50 (11 PIS) polymorphic sites for P. paludosus and P. japonica with 10 and 3 haplotypes respectively. The haplotype diversity (h) and nucleotide diversity (π) of P. paludosus samples were 0.743 ± 0.047 and 0.00183 ±0.00024. Those of P. japonica samples were 0.833 ±0.222 and 0.04396 ± 0.01253 (total: 0.784 ± 0.043 and 0.02088 ± 0.00826). Neighbor joining tree of P. paludosus , P. japonica and P. platensis ( Radulovici et al. 2009, NCBI, FJ581856 – FJ581858 ) formed three distinct clades, with bootstrap value> 99 suggesting the clades were well separated ( Fig. 9 ), and topology of BI and ML trees were essentially consistent with NJ. Average sequence divergence ( Tab. 2) of P. paludosus from P. japonica was 13.3% (11.9–15.3%) from P. japonica , which was comparable to the interspecific difference of other Platorchestia species including P. platensis ( Radulovici et al. 2009, NCBI, FJ581856 – FJ581858 ; 14.5 and 17.2%).

Platorchestia P. japonica P. japonica P. platensis Orchestia cav- Parorchestia sp. nov. Japan China imana sp.

Platorchestia sp. nov. 0.2

P. japonica ( Japan) 13.3 4.8

P. japonica ( China) 10.4 14.3 _

P. p l a t e n s i s 14.5 17.2 16.1 0.01

Orchestia cavimana 19.1 21.1 19.9 23.2 _

Parorchestia sp. 22.0 24.0 23.4 22.6 26.0 _ Discussion. In the present study, Platorchestia paludosus sp. nov. is considered as a new species based on morphological and molecular evidence. The morphology is very close to P. japonica sensu stricto ( Tattersall 1922). Miyamoto & Morino (2004) considered their material collected from North Taiwan as P. japonica and Miyamoto & Morino (2004) noted their Taiwanese specimens differed from P. japonica collected from the Lake Biwa, Japan in the degree of sexual dimorphisms in peduncle articles 4 and 5 of antenna 2 and carpus of pereopod 7, shape of coxal plate of pereopod 6 and anterodistal corner of the posterior, morphology of marginal spines in peduncles of pleopods 2 and 3 and the spine patterns in pereopod 6 and 7. In the present study, we found that P. japonica identified by Miyamoto & Morino (2004) in Taiwan was P. paludosus identified in the present study. We used scanning electron microscopy and additionally noted consistent morphological differences between P. paludosus (10 individuals) and P. japonica (4 individuals) collected from the Lake Biwa, in the distribution pattern of setae on the lateral margin of telson, and in the shape of the ramus tip of uropod 3. Platorchestia paludosus has one group of cuspidate setae type III on the lateral margin of telson, whilst P. japonica contains two groups of cuspidate setae type III on the lateral margin of telson ( Fig. 10 a). P. paludosus has a sharper ramus of uropod 3, whilst the tip of ramus in uropod 3 of P. japonica is blunt ( Fig. 10 b). However, the number of setae on peduncle of uropod 3 varied from 1–3 in both P. paludosus and P. japonica , and thus, this cannot be considered as a taxonomic important character ( Fig. 10 b).

Miyamoto & Morino (2004) divided the genus Platorchestia into three groups based on the different gradient of sexual dimorphism character of antenna 2 and pereopod 6 and 7. The “group 3” defined by Miyamoto & Morino (2004) included species “displaying no sexual dimorphism” and having “antenna 2 and pereopod 6 and 7 barely (or slightly) sexual dimorphic”. Currently six species are placed within this group, including P. japonica ( Tattersall 1922) , P. humicola , P. k a a l e n s i s, P. lanipo and P. pickeringi , and the P. paludosus in the present study also belong to this group. Platorchestia paludosus can be differentiated from P. pickeringi , P. kaalensis and P. lanipo by having normal maxilliped palps (vs. slender maxilliped palps) and differs from P. humicola by possessing longer pleopod ramus: 0.8–0.9 times as long as peduncle (v.s. 0.5–0.6 times in P. humicola ). Results from DNA barcoding further supports P. paludosus as different from P. japonica and is therefore a new species. Average sequence divergence of P. paludosus from P. japonica was 13.3% (11.9–15.3%), which is comparable to the interspecific difference P. platensis (NCBI, FJ581856 – FJ581858 ; 14.5 and 17.2%). Platorchestia platensis differs from P. japonica in the morphology of palm of mature male gnathopod 2 and degree of sexual dimorphism in antenna 2 and pereopod 6 and 7 ( Miyamoto & Morino 2004). Our phylogenetic analysis also included a COI sequence (from GenBank) of P. japonica collected from Hebei, China (NCBI, EF570353 ; Hou, Fu et al. 2007). Sequence divergence of P. japonica from China and specimens from Lake Biwa, Japan reached about 14.3% and P. japonica from China is closer to P. paludosus , in having a sequence divergence of 10.4 %. Miyamoto & Morino (2004) claimed their P. japonica collected from Taiwan had slight morphological differences (in the sharpness of coxal plate of pereopod 6 and number of margin spine in uropods 1–3) from P. japonica from China in Morino & Dai (1990). Morphological and molecular data suggests that P. japonica from the mainland China could be another cryptic species and awaits further morphological and molecular analysis.

Iwasa (1965) recorded Orchestia platensis Krøyer [= Platorchestia platensis (Krøyer) , Bousfield 1982] from Tanshui, N. Taiwan but there were no detailed text or figure illustrations for this species in Iwasa (1965). It is therefore difficult to check the validity of the record from Iwasa (1965). However, Miyamoto & Morino (2004) described their collections in Taiwan from 1976–1981 but they have not reported any P. platensis (Krøyer) , and their records in N. Taiwan were ‘ P. japonica ’.

Species name Gender Id. no. GenBank no. P. paludosus sp. nov. m Apj 1 HQ 010294

(Taipei, Taiwan.) f Apj 2 HQ 010295

f Apj 3 HQ010296

m Apj 5 HQ010297

m Apj 6 HQ010298

m Apj 7 HQ010299

m Apj 8 HQ 010300

f Apj 9 HQ010301

m Apj 10 HQ 010302

* Apj 12 HQ 010303

* Apj 13 HQ 010304

* Apj 14 HQ 010305

continued next page Species name Gender Id. no. GenBank no. f Apj 15 HQ 010306 * Apj 16 HQ 010307 * Apj 17 HQ 010308 * Apj 18 HQ 010309 * Apj 19 HQ 010310 * Apj 21 HQ010311 m Apj gp 2 HQ010312 m Apj gp 4 HQ010313 m Apj gp 5 HQ010314 m Apj gp 6 HQ010315 m Apj gp 7 HQ010316 m Apj gp 8 HQ010317 m Apj gp 9 HQ010318 m Apj gp 10 HQ010319 m Apj gp 11 HQ010320 m Apj gp 12 HQ010321 m Apj gp 13 HQ 010322 f Apj gp 14 HQ010323 m Apj gp 15 HQ010324 m Apj gp 16 HQ010325 m Apj gp 17 HQ010326 m Apj gp 18 HQ010327 m Apj gp 19 HQ010328 m Apj gp 20 HQ010329 m Apj gp 21 HQ010330 m Apj gp 23 HQ010331 m Apj gp 24 HQ010332 m Apj gp 26 HQ010333 m Apj gp 27 HQ010334 m Apj gp 28 HQ010335 m Apj gp 29 HQ 010336 P. japonica m H143-3-1 HQ 010293 (Lake Biwa, Japan.) f H143-3-2 HQ 010337 f H143-3-3 HQ010338 m H143-3-4 HQ 010339 Parorchestia sp. f H100-4-1 HQ 010292 (Lake Biwa, Japan.)

Figures

FIGURE 1. Platorchestia paludosus sp. nov. Types of setae revealed from SEM. a – f. Simple setae. g – i, Cuspidate setae, j – m Serrate setae, n. Serrulate setae, o. Plumose setae, p – q. Pappose setae, r – s Papposerrate setae, t – u. Setule.

FIGURE 3. Platorchestia paludosus sp. nov. male. R At 1, a) ventral view, b) tip, ventral view. L At 1, c) dorsal view, d) tip, dorsal view. R At 2, e) tip, inner lateral view. f) tip, outer lateral view. g) R At 2 (L one), L At 2 (R one). h) Ul, dorsal view. i) R Md, dorsal inner lateral view. j) L Md, dorsal inner lateral view. k) Ll, ventral view. l) R Mx 1, ventral view. m) L Mx 1, dorsal view. R Mx 2, n) ventral view, o) inner plate margin, ventral view, p) outer plate margin, ventral view. L Mx 2, q) dorsal view, rs) inner plate margin, dorsal view, s) outer plate margin, dorsal view. R: right; L: left; At: antenna; Ul: upper lip; Md; mandible; Mx: maxilla; Ll: lower lip; Mp: maxilliped; Pa: palp; Gp: gnathopod; Pp: perepod; Plp: pleopod; Up: uropod; Tl: telson.

FIGURE 4. Platorchestia paludosus sp. nov. male. Mp, a) R Pa and outer plate, ventral view, b) inner plate, dorsal view, c) L Pa and outer plate, dorsal view, d) Pa article 3, ventral view, e) outer and inner plate, ventral view, f) Pa article 3, dorsal view, g) Pa article 2, spines on ventral outer lateral surface, j) Pa article 2, inner distal corner, spines on ventral surface, i) Pa article 2, spines on distal outer lateral surface, j) Pa article 1, spines on ventral outer lateral surface, k) Pa article 2, spines on inner margin, l) Pa article 1, spines on distal outer lateral surface, m) Pa article 1, inner distal corner, spines on ventral surface, n) outer plate, ventral view, o) outer plate, dorsal view, p) outer plate, spines on ventral medial surface, q) outer plate, spines on medial inner lateral margin, r) inner plate, spines on ventral medial surface. For abbreviations, see legend in Fig. 3.

FIGURE 5. Platorchestia paludal sp. nov. male. a) L Gp 1 outer lateral view. b) R Gp 1 inner lateral view. c) L Gp 1 carpus posterodistal angle, outer lateral view. d) R Gp 1 carpus posterodistal angle, inner lateral view. e) L Gp 1 palm, outer lateral view. f) R Gp 1 palm, inner lateral view. g) L Gp 2 outer lateral view. h) R Gp 2 inner lateral view. i) L Gp 2 palm, outer lateral view. j) R Gp 2 palm, inner lateral view. For abbreviations, see legend in Fig. 3.

FIGURE 6. Platorchestia paludosus sp. nov. male. Pp 3, a) coxae, b) basis-dactylus, c) dactylus. Pp 4, d) coxae, e) basis-dactylus, f) dactylus. Pp 5, g) coxae, h) basis-dactylus, i) dactylus. Pp 6, j) coxae, k) basis-dactylus, l) dactylus. Pp 7, m) coxae, n) basis-dactylus, o) dactylus. Coxal gills, p) of Gp 2, q) of Pp 3, r) of Pp 4, s) of Pp 5, t) Pp 6. Brood plates, u) of Gp 2, v) of Pp 3, w) of Pp 4, x) of Pp 5. y) Pair of penial papillae. For abbreviations, see legend in Fig. 3.

FIGURE 7. Platorchestia paludosus sp. nov. male. a) R Plp 1, posterior view, b) L Plp 1, anterior view, c) R Plp 2, posterior view, d) L Plp 2, anterior view, e) R Plp 3, posterior view, f) L Plp 3, anterior view, g) L Up 1, outer lateral view, h) R Up 1, inner lateral view, i) L Up 2, outer lateral view, j) R Up 2, inner lateral view, k) L Up 3, outer lateral view, l) R Up 3, inner lateral view, m) Tl, dorsal view. For abbreviations, see legend in Fig. 3.

FIGURE 8. Platorchestia paludosus sp. nov. female. L Gp 1, a) outer lateral view, b) propodus, outer lateral view. L Gp 2, c) outer lateral view, d) merus, outer lateral view, e) propodus, outer lateral view. R Gp 1, f) inner lateral view, g) propodus, inner lateral view. R Gp 2, h) inner lateral view, i) merus, inner lateral view, j) propodus, inner lateral view. For abbreviations, see legend in Fig. 3.

FIGURE 9. Neighbour joining trees, showing bootstrap values NJ / BI / ML showing sequence divergence in Platorchestia paludosus sp. nov., P. japonica from Lake Biwa, P. japonica from China (from Genbank), P. p l a t e n s i s from Canada (from Gen- Bank) and outgroup species including Orchestia cavimana (from GenBank; see Browne et al.) and Parorchestia sp. from Japan (for details of GenBank no., see Table 3).

FIGURE 10. Platorchestia paludosus sp. nov. and P. japonica. a) telson, showing the interspecific variation in the number of setal groups at the lateral margin (indicated by white arrows). P. paludosus has one group of setae, whilst P. japonica has two groups of setae (indicated by white arrows). b) uropod, showing the interspecific differences in the shape of the ramus (indicated by white arrows). Note the intra-specific variation in number of setae in the peduncle (indicated by black arrows, for details, see discussion).