Amphipod crustaceans (Gammaridea) from Beijing, P. R. China

Seven freshwater and terrestrial amphipod species from Beijing, including one new species, Jesogammarus (Annanogammarus) debilis, are reported. A detailed description and illustrations of this new species are given and differences between these seven species are discussed. A key to the amphipods of Beijing and their distribution data are also presented.


Diagnosis
Body large and stout; peduncle of antenna 2 with few short setae, calceoli present in male; pereopods 3 and 4 with long straight setae on posterior margins; epimeral plates 2 and 3 with sharp posterodistal corners; inner ramus of uropod 3 reaching about 75% of length of outer ramus, both rami set with plumose setae.

Remarks
Gammarus lacustris was redescribed by Karaman and Pinkster (1977) based on samples from all over its distributional area, while Barnard and Dai (1988) redescribed it in detail with material from Yunnan, China. The material examined from Beijing accords well with the figures and description of G. lacustris given by Barnard and Dai (1988), except that the bases of pereopods 5-7 are a little more elongate, epimeral plates 2 and 3 without very sharp posterodistal corners and telson with one basolateral spine. Uchida, 1935 Gammarus nekkensis Uchida 1935, p 1-6; Barnard and Barnard 1983, p 463;Karaman, 1984, p 147-148;1989, p 19-35. Gammarus (Rivulogammarus) nekkensis: Barnard and Dai 1988, p Karaman (1989) based on specimens from Beijing. The present material accords well with the figures and description given by Karaman (1989), except for the variable numbers and length of setae on the margins of the uropods and urosomites. These features may be variable characters within the species.

Material examined
One male and one female, a well of Beizhai Village, Qiaozi Town, Huairou District, 5 November 2002, collected by Shuqiang Li.

Remarks
Procrangonyx limpidus is a subterranean species collected from a well in a farmyard. It is the first species of the genus Procrangonyx recorded from China and only the second species described. It differs from P. japonicus Uéno, 1930 in the following characters: inner plate of maxilla 1 with five plumose setae, inner plate of maxilla 2 with seven plumose setae, palp article 3 of mandible with A-setae, ramus of uropod 3 about five times as long as peduncle.

Remarks
Platorchestia japonica was firstly recorded as Talorchestia japonica from Lake Biwa by Tattersall (1922). Bousfield (1982) ascribed it to the genus Platorchestia. Morino and Dai (1990) redescribed P. japonica from specimens collected along the Changjiang River, China, after which this species was reported based on specimens collected from Beijing (Hou et al. 2002). The present material well accords with the figures and description of P. japonica given by Hou et al. (2002), except the variable size of the eyes and variable spines and setae on the appendages.

Etymology
This specific name debilis alludes to the body shape, which seems slender.

Diagnosis
Peduncular article 1 of antenna 1 lacking a distal spine; mandibular palp articles with setae alone; propodus of male gnathopod 2 slender; propodus palmar margin of female gnathopod 2 with weakly pectinated stiff setae; outer ramus of uropod 2 marginally bare; uropod 3 with more than three plumose setae; telson longer than maximum basal width. Upper lip ( Figure 1F): convex, with minute setae. Mandibles ( Figure 1G, H, O, P): left and right incisor with five and four teeth, respectively; left lacinia mobilis with four dentitions, right lacinia mobilis bifurcate; article 1 of palp unarmed, article 2 with seven marginal and nine submarginal setae, article 3 reaching 89% of length of article 2, with two cluster of A-setae and one B-seta. Lower lip ( Figure 1I): inner lobes absent. Maxilla 1 ( Figure 1J, K, N): asymmetrical, inner plate with 16 plumose setae medially; outer plate with 11 serrated spines apically, outer margin with setules; article 2 of left palp with six spines and four setae apically; article 2 of right palp with six spines and five setae apically.
Maxilla 2 ( Figure 1L): inner plate with a diagonal row of 16 plumose setae. Maxilliped ( Figure 1M): inner plate with one subapical spine and three apical spines; outer plate with 13 spines on medial margin and three pectinate setae apically.
Gnathopod 1 (Figure 2A, C, E): coxal plate lower and anterodistal margins setose, posterodistal corner with one stiff seta; anterior and posterior margins of basis setose; propodal palmar margin bearing seven inner and nine outer striated peg-spines, anterior margin with three groups of setae; dactylus with posterior accessory blade longer than nail, bearing one seta on outer margin and two setae on inner margin.
Gnathopod 2 ( Figure 2B, D, F, G): coxal plate lower and anterodistal margins setose, posterodistal corner with one stiff seta; anterior and posterior margins of basis setose; propodus more slender than in gnathopod 1, palmar margin bearing eight inner and eight outer striated peg-spines; dactylus with posterior accessory blade longer than nail, bearing one seta on outer margin and two setae on inner margin.
Pereopod 3 ( Figures 2H, 3A, J): coxal plate subrectangular, anterodistal margin with two setae, posterodistal margin with one seta and one stiff seta; basis with long setae on anterior and posterior margins; merus with three groups of long stiff setae on posterior margin; carpus with spines accompanied by setae on posterior margin; propodus with four single spines accompanied by setae on posterior margin; dactylus with one plumose seta on outer margin and two setae at hinge of nail.
Pereopod 4 ( Figures 2I, 3B): coxal plate excavated on posterior margin, anterodistal margin with one seta, posterodistal margin with seven setae; basis with long setae on posterior margin; merus with three groups of stiff setae on posterior margin; carpus with one spine accompanied by setae; propodus with spines accompanied by setae; dactylus similar to that of pereopod 3.
Pereopod 5 ( Figures 2J, 3C, I): coxal plate with one distal seta on anterior lobe, posterodistal corner of posterior lobe with one spine; basis with one group of setae on anteroproximal margin, anterodistal margin spinose, posterior margin nearly straight, with stiff setae; merus to propodus with marginal spines; dactylus with one plumose seta on outer margin and one seta at hinge of nail.
Pereopod 6 (Figures 2K, 3D): longer than pereopod 5, coxal plate with one spine on posterodistal corner; basis with one group of setae on anteroproximal margin and spines on anterodistal margin, posterior margin weakly sinuate, with a row of setae associated with short spines; merus to propodus with marginal spines; dactylus similar to that of pereopod 5.
Pereopod 7 (Figures 2L, 3E): coxal plate with a group of long setae on anterior margin and three short setae on posterior margin; basis with two long setae on anteroproximal margin and spines on anterodistal margin, posterior margin expanded, with short spines and setae, inner surface bearing one posterodistal spine and one seta; merus to propodus with marginal spines; dactylus similar to that of pereopod 5.
Coxal gills of gnathopod 2 and pereopods 3 and 4 subequal to their bases in length ( Figure 2G-I), anterior accessory lobe of each gill larger than posterior lobe, about onequarter of main gill in length. Gill of pereopod 5 ( Figure 2J) longer than basis, anterior accessory lobe larger than posterior lobe, about one-third of main gill. Gill of pereopod 6 ( Figure 2K) shorter than basis, accessory lobe about half of main gill. Gill of pereopod 7 ( Figure 2L) a little longer than half of basis, accessory lobe less than one-quarter of main gill.   Pleopods 1-3 ( Figure 3F-H): subequal in length, peduncle with long setae on outer margin, bearing two retinacula accompanied by three or four plumose setae on anterodistal corner; outer ramus a little shorter than inner ramus, both rami armed with plumose setae.
Urosomites ( Figure 4F): urosomites 1 and 2 bearing a pair of dorsomarginal lateral spines and medial spine-clusters associated with setae; urosomite 3 with a pair of dorsomarginal lateral spines and two medial setae.
Uropod 1 ( Figure 3K): basofacial spine in peduncle present or absent, outer and inner margins with two or three spines, respectively; outer ramus with three spines on inner margin; inner ramus with two spines on inner margin.
Uropod 2 ( Figure 3L): peduncle with marginal spines on inner and outer margins; outer ramus marginally bare; inner ramus with one spine on outer margin and two spines on inner margin.
Uropod 3 ( Figure 3M): peduncle with short setae on inner margin; outer ramus with two articles, outer margin of proximal article with one spine and two pairs of spines sequentially, inner margin with seven plumose setae and a pair of spines; terminal article distinct, 18% of length of proximal article, longer than distal spines of proximal article; inner ramus about one-third of proximal article, with one spine and two plumose setae on inner margin, and one apical spine accompanied by one plumose seta.
Gnathopod 1 ( Figure 5A, C, E, G, H): coxal plate with setae on lower and posteroproximal margins; basis with numerous long setae on anterior and posterior margins; propodus oval, bearing two spines on inner posterodistal corner and two spines on outer posterodistal corner, and five pectinate stiff setae; dactylus with posterior accessory blade shorter than nail, bearing one seta on outer margin.
Gnathopod 2 ( Figure 5B, D, F, I): coxal plate with one seta on anterodistal corner and 15 setae on posterior margin; basis with setae along anterior and posterior margins; carpus and propodus slender, propodus parallel-sided, palmar margin with five simple spines on inner margin and three simple spines and two weakly pectinate stiff setae on outer margin; dactylus with posterior accessory blade shorter than nail, bearing one seta on outer margin.
Pereopod 3 (Figures 5J, 6A): coxal plate with setae on posterior margin; basis with long setae on anteroproximal and posterior margins; merus and carpus with long stiff setae on posterior margin; propodus with spines on posterior margin.
Pereopod 4 ( Figure 6B): coxal plate with setae on posterior margin; basis with long setae on posterior margin; merus with stiff setae on posterior margin.
Pereopod 6 ( Figure 6D): coxal plate with long setae on anterior margin; basis with two groups of setae and one posterodistal seta on inner surface.  Pereopod 7 ( Figure 6E, I): coxal plate with two groups of long setae on anterior margin; basis with numerous long setae and one posterodistal spine on inner surface.
Accessory gills: anterior lobe of accessory gills of gnathopod 2 and pereopod 3 much larger than posterior lobe; anterior lobe of accessory gill of pereopod 4 a little larger than posterior lobe; anterior lobe of accessory gill of pereopod 5 about one-third of main gill; accessory gill of pereopod 6 about half of main gill; accessory gill of pereopod 7 about onethird of main gill.
Uropod 1 ( Figure 6F): peduncle with or without basofacial spine, bearing marginal spines; outer ramus with one spine on inner margin; inner ramus with two spines on inner margin.
Uropod 3 ( Figure 6H): proximal article of outer ramus with two groups of spines on outer margin, inner margin with three plumose setae and one spine, and bearing two pairs of distal spines, reaching half of terminal article length; terminal article 23% of length of proximal article; inner ramus 40% of length of proximal article, with one spine and two plumose setae on outer margin.

Variation
Basofacial spine on peduncle uropod 1 present or absent in males and females.

Conclusion and discussion
Based on intensive collection of amphipods in Beijing over the last 10 years, and other collections in IZCAS dated to 1928, seven freshwater and terrestrial amphipod species are now known from Beijing. A key to the males of all species is given below. Procrangonyx limpidus is the only subterranean crustacean found in Beijing and only two individuals were collected. Whenever we talked with the local people during our collection, many farmers told us that they have seen subterranean crustaceans before, but none after 1990. This is obviously a result of over-exploitation and exhaustion of the groundwater in Beijing. In fact, due to the high speed of economic development, over-population, changing climate and deterioration of water resources, the level of the groundwater in Beijing has been reduced and reduced (Tang et al. 2004).
Meanwhile, due to a decline in surface water, some terrestrial amphipods also became limited in distribution. Jesogammarus (Jesogammarus) hebeiensis could be found in Hehua Pond in the campus of Tsinghua University in 1929 but Hehua Pond is now filled with water transferred from another area and amphipods cannot be found there today.
In general, today's distribution pattern of amphipod crustaceans from Beijing is a result of both natural and anthropogenic changes. A study of the meta-population of amphipod crustaceans based on molecular techniques and rich collections from Beijing is being conducted by the same authors and further comments on the distribution patterns of amphipod crustaceans will follow.