Heterokamaka lutensis sp. nov.

Figures 2–7

Material examined. Holotype: male (IZCAS-I-A1044-1), 3.3 mm, Dianshan Lake (121.1° E, 31.5°N), Shanghai, China, 20 June, 2006, collected by Liqing Wang and Ruilei Zhang. Paratypes: 1 female (IZCAS-I- A1044-2), 3.2 mm; 1 male (IZCAS-I-A1044-3), 3.1 mm, same data as holotype.

Diagnosis. Eyes absent. Antenna 1 with long setae along ventral margin. Peundular article 5 of antenna 2 with serrated posterior margin. Mandibular palp lamellate in article 3, armed with long setae. Gnathopod 2 strong, with a big process on posterior margin of propodus. Pereopods 5–7 with plumose setae on posterior margin of basis.

Description of male. Holotype, male 3.3 mm.

Head: (Fig. 2 A) Rostrum short, ocular lobe extended, eyes absent, inferior antennal sinus deep.

Antenna 1: (Fig. 3 A) Pedundular articles 1–3 in length ratio 1: 1.14: 0.98, distoventral corner of peduncular article 1 with 2 setae and 1 plumose seta, article 2 and 3 armed with long setae along ventral margins; flagellum with 8 articles, articles 6–8 each with 1 aesthetasc at distal end; accessory flagellum absent.

Antenna 2: (Fig. 3 B) About 1.2 times as long as antenna 1; peduncular articles 3–5 in length ratio 1: 2.2: 2.1, articles 4 and 5 broad, posterior margin of article 5 serrate, with short setae along dorsal and ventral margins; flagellum with 8 articles, articles 1–5 broadened distally, with short setae.

Upper lip: (Fig. 3 C) Ventral margin with minute setae.

Mandibles: (Fig. 3 D, E) Right mandible incisor with 2 proximal teeth and 3 small dentitions; lacinia mobilis bifurcate, with 2 or 4 dentition each; spine row with 2 stout plumose setae; palp articles in length ratio 1: 3.1: 2.5, article 2 with 7 lateral and 5 distal setae, article 3 lamellate, broadened distally, with 6 setae on medial surface, 8 setae on lateral margin and heavily setose on ventrodistal margin. Left mandible incisor with 4 teeth; lacinia mobilils bifurcate, with 2–3 teeth each.

Lower lip: (Fig. 3 F) Inner plates and outer plates with short setae.

Maxilla 1: (Fig. 3 G) Outer plate with 9 or 10 stout setae apically; palp with 2 articles, article 2 with 4 stout setae, 3 stiff setae, and 1 small spine.

Maxilla 2: (Fig. 3 H) Inner and outer plates with long setae apically.

Maxilliped: (Fig. 3 I) Inner plate bearing 4 stiff setae and 4 plumose setae apically; outer plate not exceeding apex of article 2 of palp, medial margin armed with setae, bearing 4 stout plumose setae apically; plap with 4 articles, article 3 with long setae distally, article 4 stout, with 1 lateral seta and several distal setae.

Gnathopod 1: (Fig. 4 A, B) Coxal plate produced anteriorly, bearing 22 long setae on anteroventral margin; basis with 2 long setae on posterior margin; carpus with parallel margins, bearing 7 clusters of long setae along ventral margin, 3 long setae on dorsal margin and 5 clusters of long setae on medial surface; propodus oval, with long setae on medial surface and palmar margin; dactylus with 1 seta on posterior margin and 2 short setae on anterior margin.

Gnathopod 2: (Fig. 4 C) Coxal plate excavated anteriorly, bearing 4 short setae on ventral margin and 1 spine on posterior margin; basis elongate, with 1 distal seta; carpus triangular; propodus enlarged, with long, acute posterior process on proximal corner, the process derived from one-third of posterior margin, not exceeding distal margin of propodus, with 3 setae on lateral margin of process; dactylus curved, with a row of 6 setae on medial surface, several short setae on anterior and posterior margins.

Pereopod 3: (Fig. 4 D) Coxal plate weakly excavated anteriorly, with 5 setae on ventral margin and 1 spine on posterior margin; basis with short setae on anterior margin; merus with long setae on anterodistal corner; carpus about 0.6 times the length of propodus, with long setae on distal corners; propodus narrowed distally, with short setae on posterior margin; dactylus slender.

Pereopod 4: (Fig. 4 E) Similar to pereopod 3, coxal plate rounded on anterior margin, with 5 setae on ventral margin and 2 spines on posterior margin; dactylus with 1 seta on posterior margin.

Pereopod 5: (Fig. 5 A, D) Short, coxal plate wide, anterior lobe with 5 setae on ventral margin, posterior lobe with 1 plumose seta on posteroventral corner; basis with 5 plumose and 2 simple setae on anterior margin and 5 simple setae on anterodistal corner, posterior margin weakly narrowed distally, with 4 plumose setae and 2 simple setae; merus with setae on anterior and posterior distal corners; carpus dilated distally, about 0.4 times the length of propodus, with 3 spines on posterodistal corner; propodus with short marginal setae and 1 stiff plumose seta distally; dactylus curved.

Pereopod 6: (Fig. 5 B) Anterior lobe of coxal plate with 1 seta on anterior margin, posterior lobe with 1 seta on posteroventral corner; basis elongate, with 13 plumose setae on anterior margin and 4 short setae on anterodistal corner, and 9 plumose and 8 simple short setae on posterior margin; merus with 2 setae on posterior margin; carpus about half the length of propodus, with 2 spines on posterior margin and 4 spines on posterodistal corner; propodus with short setae on anterior and posterior margins, and 1 plumose seta on distal margin; dactylus with 1 minute seta on posterior margin.

Pereopod 7: (Fig. 5 C) Longer than pereopod 6, coxal plate scarcely lobate, anterior margin with 1 seta; basis with 2 simple setae on anterior margin, 2 setae on anterodistal corner, 16 plumose and 8 simple setae on posterior margin; merus with 1 and 2 setae on anterior and posterior margins, respectively; carpus about half the length of propodus, with 3 setae on anterodistal corner and 4 spines on posterodistal corner; propodus with short setae along anterior and posterior margins, and 4 simple and 1 plumose setae distally; dactylus long, curved.

Coxal gills: Present on gnathopod 2 and pereopods 3–6, sausage-shaped.

Pleopods 1–3: (Fig. 5 E–G) Similar, peduncle with marginal plumose setae and 1 or 2 retinacula; outer ramus shorter than inner ramus, outer ramus with 8, 7, 7 articles and inner ramus with 10, 10, 9 articles for pleopod 1, 2 and 3.

Urosomites 1 and 2: (Fig. 5 I) Coalesced.

Uropod 1: (Fig. 5 H) Peduncle with 2 spines on outer margin and 1 spine on inner distal corner, ventrodistal process curved; outer ramus shorter than inner ramus, bearing 2 spines on outer margin; inner ramus with 1 seta, both outer and inner rami with 4 terminal spines.

Uropod 2: (Fig. 5 I) Peduncle with 1 spine on outer distal corner; outer ramus shorter than inner ramus, with 2 spines on outer margin; inner ramus with 1 spine on outer margin, both rami with 4 terminal spines.

Uropod 3: (Fig. 5 I, J) Peduncle as long as ramus, ramus with long terminal setae.

Telson: (Fig. 5 J) Not coalesced with urosomite 3, with 1 simple and 1 plumose setae on dorsodistal margin.

Description of female. 3.2 mm (Fig. 2 B).

Antenna 1: (Fig. 6 A) Peduncular articles 1–3 in length ratio 1: 1: 0.9, articles 2–3 with long setae along ventral margin; flagellum with 7 articles, armed with long setae on ventral margin, the last article with 1 aesthetacs.

Antenna 2: (Fig. 6 B) Peduncular articles 3–5 in length ratio 1: 2: 2, article 3 with long setae on posterodistal corner, articles 4–5 with long setae on posterior margin, article 5 not serrate; flagellum with 6 articles, armed with long setae on posterior margin.

Gnathopod 1: (Fig. 6 C, D) Coxal plate dilated anteriorly, densely with long setae on anterior and ventral margins, posterior margin with 1 spine; basis with more setae than that of male.

Gnathopod 2: (Fig. 6 E) Coxal plate excavated on anterior margin, bearing 9 setae on ventral margin and 3 stiff setae on posterior margin; propodus elongate, palm with 1 spine and long setae; dactylus with 1 seta on posterior margin and 3 short setae on anterior margin.

Pereopod 3: (Fig. 6 F) Coxal plate weakly excavated anteriorly, with 9 setae on ventral margin and 2 spines on posterior margin; basis with long setae on posterior margin; merus and carpus weakly dilated.

Pereopod 4: (Fig. 7 A) Coxal plate with 10 setae on ventral margin and 2 spines on posterior margin; basis with long setae on posterior margin, merus and carpus with distal setae.

Pereopod 5: (Fig. 7 B) Coxal plate broad, anterior lobe with 9 setae on ventral margin, posterior lobe with 1 plumose seta on posteroventral corner; basis with 4 plumose and 3 simple setae on anterior margin and 3 setae on anterodistal corner, posterior margin with 6 plumose and 5 simple setae; carpus dilated distally, with 2 spines on posterior margin and 5 spines on posterodistal corner; propodus with 3 setae on anterior margin; dactylus with 1 plumose seta on posterior margin.

Oostegite: Oostegite on gnathopod 2 very small (Fig. 7 C), with 3 setae distally; oostegites on pereopod 3– 5 elongate (Fig. 7 D–F), with long setae.

Etymology. The species name ‘lutensis’ alludes to its habitat, living in the muddy bottom.

Habitat. So far only known from freshwater muddy bottom, two meters in depth.

Remarks. Heterokamaka lutensis sp. nov. is the second species of Heterokamaka. The new species differs from the type species H. isahayae Ariyama, 2008 in eyes absent, while present and situated distal to ocular lobes for H. isahayae; in propodus of gnathopod 2 with a large process, while posterodistal large process with short hook in the middle for H. isahayae; carpus of pereopod 5 dilated distally, while normal for H. isahayae.

All species of Kamaka and Heterokamakar are tube-dwelling amphipods, however, H. lutensis sp. nov. is the only one which has no eyes. Ariyama (2008) reported that H. isahayae is probably facing a high risk of extinction, because of eutrophication of the habitat. H. lutensis sp. nov. is threatened by similar reasons. The type locality, Dianshan Lake, has become hyper-eutrophicated (Cheng & Li, 2008), which may result in the reduction of population size.