Macrobrachium elegantum Pan 2010

Macrobrachium elegantum Pan et al., 2010 Macrobrachium elegantum Pan et al., 2010: 86, figs 2–4. Type locality: a cave in Xiaorui Village, Ludong Town, Jingxi County, Guangxi, China. Material examined. None. Diagnosis. Body semi-transparent. Carapace and abdomen smooth and glabrous. Rostrum straight, tip bifurcate and reaching beyond end of scaphocerite, 0.7 times of cl. Dorsal margin armed with 7 or 8 teeth, including 3 or 4 teeth behind orbit. Dorsal teeth placed more widely on anterior part. Ventral margin armed with 4 to 6 teeth. Eyes with cornea totally degenerated. Ocular peduncle small, elliptical and non-pigmented. Scaphocerite about 3.0 times longer than wide. Second pereiopod slender, subequal in size and similar for both sexes. Ischium 0.9 times as long as merus; merus as long as carpus; carpus 1.5 times as long as palm; finger 1.7 times as long as palm, palm slightly inflated. Distribution. Jingxi County, Guangxi, China. Remarks. Macrobrachium elegantum is typical of a stygobitic organism, characterized by the complete absence of body color and the degeneration of eyes. In addition, the morphology of this species is distinctly different from that of other stygobitic species, thus supporting the validity of the species. This species differs from all epigean species as well as M. parvum sp. nov. and M. tenuipes by the completely degraded somatic pigmentation and eyes. It can be distinguished from M. duanense, M. guizhouense sp. nov. and M. lingyunense by the bifurcate tip of rostrum (unicuspidate in other three species), the different rostral formula (3–4 + 3–4 / 4–6 in M. elegantum vs. 2–3 + 6–7 / 2–4 in M. duanense), the slender scaphocerite (3.0 times longer than wide in M. elegantum, vs. 2.2 to 2.4 times in other three species) and the different ratios between the segments of second pereiopods (Table 4).