Platorchestia japonica (Tattersall, 1922)

Hou, Z. - E. & Li, S., 2003, Terrestrial talitrid amphipods (Crustacea: Amphipoda) from China and Vietnam: studies on the collection of IZCAS, Journal of Natural History 37, pp. 2441-2460 : 2442-2448

Platorchestia japonica (Tattersall, 1922)

(figures 1–4)

Talorchestia japonica Tattersall, 1922: 452 , pl. XXI, figures 1–10.

Platorchestia japonica Bousfield, 1982: 27 .

Platorchestia japonica Morino and Dai, 1990: 7 , figures 9–11.

Material examined. Sixty-five males and 24 females (one male and one female were illustrated in this paper); paddyfield north-west of Beijing; 22 August 2000; collected by Shuqing Li and Zhong-e Hou. Other material from the following localities was also examined. Five males and five females; a river at the foot of Mt Yuquanshan , Beijing; 22 May 2001; collected by Shuqiang Li and Zhong-e Hou. Four males, eight females and four juveniles; Lake Xuanwuhu, Nanjing ; 22 September 1988; collected by Shuqiang Li and H. Morino. Four females and six juveniles; Yanghe River , Shanghai; 26 September 1988; collected by Shuqiang Li. Two females; Lake Donghu, Wuhan ; 18 September 1988; collected by Hiroshi Morino. Fifteen males, 52 females and 15 juveniles; Lake Taihu, Wuxi ; 23 September 1988; collected by H. Morino and Shuqiang Li. Fourteen males and 27 females; Lake Nanhu, Wuhan ; 12 September 1988; collected by Shuqiang Li and H. Morino.

Description. Male (IZCAS-I-A0013), body length 8.5 mm. Eyes subcircular, based on the basis of antenna 1, about 0.36 times of head diameter. Inferior antennal sinus distinct. Buccal mass directed beneath head. Antenna 1 short, barely reaching end of peduncular article 4 of antenna 2; peduncular articles 1–3 subequal in length; flagellum four-articulate. Antenna 2: peduncular article 5 a little longer than article 4, with short spines along both margins; flagellum 12-articulate, each article with some bristles.

Upper lip convex, with minute setae. Left mandible: incisor five-dentate, lacinia mobilis with five weak teeth, molar triturative with one long seta. Right mandible: incisor five-dentate, lacinia mobilis bifurcate, with weak definitions. Lower lip concave, with fine setae, inner lobes lacking. Maxilla 1 with rudimentary palp, inner plate with two plumose distal setae, outer plate with nine apical serrated spines. Maxilla 2: inner plate with one plumose seta at medial margin, outer plate armed with two rows of incurved setae. Maxilliped: inner plate with three spines and some plumose setae on distal margin; outer plate with slender spines on medial margin; article 2 of palp broad, article 4 distinct, positioned on subdistal part of dorsal surface.

Gnathopod 1: coxal plate anteriorly rounded, ventral margin spinose; basis straight and narrow, both anterior and posterior margins with short spines; merus without tumescent humps, posterior margin spinose; carpus subtriangular-shaped, with tumescent humps at posterodistal angle, and a row of long spines at base of hump; propodus about 0.6 times as long as carpus, with tumescent hump at posterodistal angle, with rows of spines, palmar margin with some stiff setae; dactylus shorter than palm of propodus, bearing one seta at joint of nail. Gnathopod 2: coxal plate spinose, with cuspidate posterior margin; anterior margin of basis bare, posterior margin with four small spines; propodus large, oval, palmar margin smoothly convex and fringed with many spines; dactylus attenuated distally, with fine setae.

Pereopod 3 longer than pereopod 4, coxal plates with posterior cusp; carpus of pereopod 4 shorter than that of pereopod 3; propodus with a distal spine at dactylar hinge; dactylus cuspidactylate, with a stiff spine on concave margin.

Pereopod 5 about as long as pereopod 3, coxal plate anterolobate, with two and three setae on ventral and posterior margins, respectively; posterior margin of basis expanded roundly, armed with five short spinules, anterior margin of basis with seven spines; dactylus cuspidactylate, about 0.35 times as long as article 6. Pereopod 6 much longer than pereopod 5, coxal plate posterolobate, with two posterior marginal setae; basis subrounded with 10 anterior spines and six posterior setae; dactylus slender, about 0.37 times of article 6 in length. Pereopod 7 slightly longer than pereopod 6, coxal plate non-lobate, ventral margin with three short setae; basis strongly expanded, with 10 short spines on anterior margin and 14 setae on posterior margin; dactylus 0.38 times as long as article 6.

Coxal gill of gnathopod 2 anchor-shaped, gills of pereopods 3 and 4 hooked at middle, gills of pereopods 5 and 6 subcircular.

Epimeral plates with slightly pointed posterior angles, ventral margin unarmed, posterior margin with two or three minute setae. Pleopods well developed, peduncles with two retinaculae, peduncle of pleopod 3 postero-distally setulose, with five short spines along intero-posterior margin; both rami fringed with plumose setae.

Uropod 1: peduncle longer than rami, with three and four spines on inner and outer margins, respectively; outer ramus a little shorter than inner ramus, outer ramus marginally bare, with three distal spines; inner ramus with one inner marginal and three outer marginal and four distal spines. Uropod 2: peduncle with three and four spines on inner and outer margins, respectively, inner ramus with one mid-marginal spine, outer ramus with one and two spines on inner and outer margins, respectively, both rami with distal spines. Uropod 3: peduncle with two spines on distal corner, ramus slightly shorter than peduncle, with two lateral and three distal spines.

Telson longer than wide, apically notched, each lobe with two to three distal spines and one sublateral spine.

Dimorphism. Female (IZCAS-I-A0014) 8.6 mm. Gnathopod 1: carpus and propodus not tumescent, propodus about 0.53 times as long as carpus, parallel-sided, with many spines along posterior margin, palmar margin short, with four slender spines at posterodistal corner; dactylus exceeding palmar margin. Gnathopod 2: coxal plate with cuspidate posterior margin; basis anteriorly broadened, anterior margin with many minute spines evenly, posterior margin with few spines; merus with small facial spines; carpus and propodus tumescent posteriorly; propodus with spine-row on lateral surface, palm margin with five stiff setae; dactylus about half of palmar margin, with a seta at hinge of nail.

Uropod 3: peduncle with two subdistal and one distal spine, ramus with one subdistal and four distal spines.

Oostegites of pereopods 2–4 elongate, parallel-sided, with dozens of setae; oostegite of pereopod 5 triangular, with 10 setae on distal margin and two spines on surface.

Remarks. Tattersall (1922) firstly recorded Talorchestia japonica from Lake Biwa. Bousfield (1982) ascribed it to the genus Platorchestia Bousfield according to the following characters: (1) left mandibular lacinia five-dentate; (2) male gnathopod 1 with tumescent carpus and propodus; (3) gnathopod 2 powerfully subchelate; (4) female gnathopod 2 with anteriorly broadened basis and posteriorly tumescent carpus and propodus; (5) carpus of pereopod 4 short; and (6) marginally unarmed outer ramus of uropod 1. Morino and Dai (1990) redescribed Platorchestia japonica with material from China. The present material well accords with the figures and description of P. japonica given by Morino and Dai (1990), except that the eyes are less than 40% of the diameter of the head and the pleopods have many packs. These features may be the result of a small size and parasites.

Habitat. P. japonica is distributed along the Yangtze River and the shore of the Jingmiyinshuiqv River , Beijing. All material was found under decaying straw or silt beside the water .