Macrobrachium duanense Lan et al., 2017

Macrobrachium duanense Lan et al., 2017

Figs 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Macrobrachium duanensis Lan et al., 2017: 61, figs 1–3. Type locality: a cave in Nongchi village, Gaoling Town, Du’an County, Guangxi, China.

Material examined.

• 2 males ( IBGAS - Dec-Pal- 490-1 – 2) (tl 53.7–78.2 mm, cl 15.3–20.5 mm, rl 7.2–9.3 mm) and 2 females ( IBGAS - Dec-Pal- 490-3 – 4) (tl 56.4–67.7 mm, cl 14.0– 17.3 mm, rl 7.4–7.8 mm), Guangxi, Du’an Yao Autonomous County, Disu Town, Xiadiao Village, Shuiyuandi Cave , 24.0061°N, 107.9840°E, 10.IV.2024, Zhou JJ. leg GoogleMaps . • 4 females ( IBGAS - Dec-Pal- 491-1 – 4) (tl 52.7–86.9 mm, cl 13.0– 24.5 mm, rl 6.2–11.2 mm), Guangxi, Du’an, Gaoling Town, Nongguangshang cave , 24.0095°N, 108.0824°E, alt. 198 m, 16.IV.2023, Zhou JJ. leg GoogleMaps . • 3 females ( IBGAS - Dec-Pal- 492-1 – 3) (tl 39.2–73.1 mm, cl 11.3–19.3 mm, rl 5.3–7.9 mm), Du’an, Nongshui Village, Nongshuitun Cave , 23.8413°N, 107.9981°E, 10.IV.2024, Zhou JJ. leg GoogleMaps .

Description.

Body moderately robust (Fig. 5 View Figure 5 ). Rostrum short and broad, reaching 3 / 4 to 4 / 5 of scaphocerite, 0.4–0.5 times of cl, slightly convex above orbital margin. Dorsal margin with 8–10 teeth (mode 9), including 2–3 teeth behind orbit, starting from about 1 / 4 of carapace length. Dorsal teeth equally spaced, except most posterior tooth more widely spaced than others. Ventral margin with 2–4 teeth (Fig. 6 A View Figure 6 ).

Eyes with cornea totally degenerated. Ocular peduncle small, elliptical and non-pigmented (Figs 5 View Figure 5 , 6 A View Figure 6 ).

Carapace (Figs 5 View Figure 5 , 6 A View Figure 6 ) smooth and glabrous. Antennal spine small, tip reaching anterolateral margin of carapace. Hepatic spine small, lying behind and below antennal spine.

Abdomen (Fig. 5 View Figure 5 ) smooth and glabrous. First to third pleurites broadly rounded, fourth and fifth pleurites slightly produced posteriorly. Sixth somite 1.2–1.5 times as long as fifth somite, with posteroventral angle slightly protruded.

Telson 1.5 times length of sixth segment, 0.4–0.5 times of cl. Tapered posteriorly, with a sharp point. Dorsal surface with two pairs of spines, occasionally with 1 or 3 teeth. Posterior margin bearing two pairs of lateral spines. Inner spines obviously longer than outer spines, with plumose setae between inner spines (Fig. 7 I View Figure 7 ).

Antennule (Fig. 6 B View Figure 6 ) with sharp stylocerite, reaching about half of basal segment of antennular peduncle. Basal segment broad, about 2 times as wide as second segment, as long as wide; distolateral spine of basal antennular segment slender, reaching beyond half of second segment. Second segment ca. 0.4 times as long as basal segment, ca. 0.5 times as long as distal segment. All segments except distal segment with submarginal plumose setae.

Scaphocerite about 2.4 times longer than wide. Inner margin somewhat convex, lateral margin strait, with stout distolateral tooth, not reaching anterior margin (Fig. 6 C View Figure 6 ).

Mandible typical of genus, with three-segmented palp, distal segment slightly longer than the other two segments; incisor process with three sharp teeth; molar process robust, truncate distally (Fig. 6 D View Figure 6 ).

Maxillular palp bilobed, upper lobe slender, slightly longer than lower lobe, with few setae distally; lower lobe stout and small, no setae. upper lacinia broadly elongated, distal margin with rows of strong spines, lower lacinia shorter than upper lacinia, tapering distally, densely setose (Fig. 6 E View Figure 6 ).

Maxilla with simple palp; basal endite deeply bilobed, upper and lower lobes subequal and digitiform, with numerous simple setae distally; scaphognathite broad, about 3.8 times as long as wide (Fig. 6 F View Figure 6 ).

First maxilliped with simple and small palp, basal and coxal endites distinct, tip of flagellum of exopod densely setose, epipod deeply bilobed (Fig. 6 G View Figure 6 ).

Second maxilliped with 5 - segmented endopod, flagellum with numerous plumose setae distally, epipod simple, with developed podobranch (Fig. 6 H View Figure 6 ).

Third maxilliped with robust endopod; antepenultimate with row of simple setae on inner margin; penultimate 0.6 times length of antepenultimate, with rows of long, simple setae on inner margin; ultimate segment about 0.8 times penultimate segment, with rows of long, simple setae on inner and outer margins; exopod well developed, reaching 0.8 times the length of antepenultimate, with plumose setae distally (Fig. 7 A View Figure 7 ).

First pereiopod slender, reaching beyond end of scaphocerite. Ischium 0.6 times as long as merus; merus as long as carpus; carpus 1.7 times as long as chela; finger 1.2 times as long as palm (Fig. 7 B, C View Figure 7 ).

Second pereiopod moderately robust, subequal in size, similar in both sexes. Merus 1.5 times as long as the ischium; carpus 0.9 times as long as merus, 1.1 times as long as palm; palm slightly inflated; finger 1.4 times as long as palm, glabrous (Figs 7 D, E View Figure 7 ).

Third pereiopod slender, merus 1.8 times as long as carpus; carpus 0.5 times as long as propodus; propodus 5.7 times as long as dactylus with several small spines on ventral margin (Fig. 7 F View Figure 7 ).

Fourth pereiopod longer than third pereiopod, generally similar in form (Fig. 7 G View Figure 7 ).

Fifth pereiopod slenderer and longer than third. merus 1.4 times as long as carpus; carpus 0.6 times as long as propodus; propodus 8.9 times as long as dactylus, with several small spines on ventral margin; dactylus terminating in a small claw (Fig. 7 H View Figure 7 ).

Male first pleopod with endopod shorter than half length of exopod, inner margin concave, outer margin slightly convex.

Male second pleopod with well-developed appendix masculina bearing numerous spiniform setae. Appendix interna digitiform, reaching to 0.6 length of appendix masculina.

Uropodal diaeresis with inner movable spine shorter than outer angle.

Color.

Body semi-transparent to golden yellow, all appendages semi-transparent (Fig. 5 View Figure 5 ).

Distribution.

Du’an County, Guangxi, China.

Habitat.

Nongshuitun Cave is similar to Nonglitun Cave and Shuiyuandi Cave, featuring broad pools in the dark zone 50–100 meters from the entrance, which may overflow out of the cave during the rainy season.

Remarks.

As a stygobiotic 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 diagnosed from M. elegantum by the unicuspidate tip of rostrum (bifurcate in M. elegantum ), the broader scaphocerite (2.4 times longer than wide in M. duanense vs. 3.0 in M. elegantum ), the different rostral formula (2–3 + 6–7 / 2 – 4 in M. duanense vs. 3–4 + 3–4 / 4 – 6 in M. elegantum ) and the different ratios between the segments of second pereiopods. This species is very similar to its sister species, M. guizhouense sp. nov. and M. lingyunense , but it can be distinguished by the palm of second pereiopods longer than ischium (shorter in M. guizhouense sp. nov. and M. lingyunense ) (Table 4 View Table 4 ).

In the original description, Lan et al. (2017) used two spellings for the species name: ‘ Macrobrachium douanensis ’ in the Chinese description and ‘ M. duanensis ’ in the English title and abstract. Here, we adopt ‘ duan - ’ (the correct spelling of the county name) and adjust the suffix to ‘ - ense’ to match the neuter gender of the genus name (ICZN Articles 31.2 and 32.2, International Commission on Zoological Nomenclature, 1999).

The type locality of this species is a cave in Nongchi Village. Although we were unable to access the exact type locality, we collected specimens from three nearby caves, apart approximately 2 km (Nongguangshang Cave) to 25 km (Nongshuitun Cave) away. Given the extensive connectivity of the local cave system and the morphological congruence between our specimens and the original description, these specimens can be regarded as topotypes.

The original description and the figures of this species are poor. In addition, the authors only compared it to the epigean and widespread species M. nipponense , rather than the stygobiotic species M. lingyunense . These hamper the correct identification of this species. Here, we redescribe this species and the results of the molecular delimitation analyses based on the topotypes of the two species, M. duanense and M. lingyunense , confirmed that they are two different species.