Megapleonum yangdongense, Huang & Shih & Ahyong, 2025

Huang, Chao, Shih, Hsi-Te & Ahyong, Shane T., 2025, Four new freshwater crab species of the genus Megapleonum Huang, Shih & Ahyong, 2018 (Crustacea, Decapoda, Potamidae) from Guangdong, China, ZooKeys 1244, pp. 1-27 : 1-27

publication ID	https://doi.org/10.3897/zookeys.1244.148112
publication LSID	lsid:zoobank.org:pub:CCCA8237-6587-44BD-A25E-41BD00928A11
DOI	https://doi.org/10.5281/zenodo.15791874
persistent identifier	https://treatment.plazi.org/id/9E1C850A-B36F-51BD-9223-39DC594E89F8
treatment provided by	ZooKeys by Pensoft
scientific name	Megapleonum yangdongense
status	sp. nov.

Treatment

Megapleonum yangdongense sp. nov.

Figs 8 View Figure 8 , 9 View Figure 9 , 10 View Figure 10 , 11 C, D View Figure 11 , 13 D View Figure 13

Type material.

Holotype: • SYSBM 002152 , male (17.8 × 14.5 mm), Gaozhai , Yangdong County, Yangjiang City, Guangdong Province, China, 21.97°N; 112.07°E, under rocks in hillstream, coll. Chao Huang, Hsi-Te Shih and Bernhard Bein, 1 June 2019 GoogleMaps . Paratypes: • SYSBM 002153 , male (17.3 × 13.7 mm), same data as holotype. SYSBM 002154 –002155 , 2 females (16.0 × 12.4 mm, 15.3 × 12.0 mm), same data as holotype GoogleMaps . IHB, 2 males (16.0 × 12.7 mm, 15.4 × 12.0 mm), same data as holotype GoogleMaps . NCHUZOOL 15306 , 2 males (16.0 × 13.1 mm, 14.9 × 11.8 mm), 1 female (16.0 × 12.6 mm), NCHUZOOL 15307 , 1 male (16.7 × 13.8 mm), same data as holotype GoogleMaps .

Diagnosis.

Carapace broader than long, dorsal surface slightly convex, postorbital, epigastric cristae confluent, sharp (Fig. 8 View Figure 8 ). Maxilliped 3 merus width ~ 1.3 × length; ischium width ~ 0.7 × length; exopod reaching slightly beyond anterior edge of ischium; flagellum short, as long as dactylus (Fig. 10 A View Figure 10 ). Ambulatory legs without long setae, pereiopod dactylus shorter than propodus (Fig. 8 View Figure 8 ). Male anterior thoracic sternum very broad, width ~ 1.9 × length (Fig. 9 B View Figure 9 ). Male pleon large, broadly triangular, pleonite 6 width ~ 2.4 × length, telson width ~ 1.8 × length (Fig. 9 C View Figure 9 ). Female pleon subovate (Fig. 9 E View Figure 9 ). G 1 large, sinuous, tip exceeding suture between thoracic sternites 4 / 5 in situ (Fig. 9 D View Figure 9 ); subterminal segment length ~ 2.7 × length of terminal segment (Fig. 10 C – E View Figure 10 ); subterminal segment thick, outer margin strongly concave, distal end slanted with outer-distal section highest; terminal segment short, both lateral margins slightly convex, bifurcated with one point being opening tip and other a smaller projection on outer margin, both pointing upwards (Figs 10 C – E View Figure 10 , 11 C, D View Figure 11 ). G 2 subterminal segment thick, slightly bent outwards distally, flagelliform terminal segment thin, ~ 2.3 × length of subterminal segment (Fig. 10 B View Figure 10 ).

Description.

Carapace broader than long, males ~ 1.2–1.3 × as wide as long (n = 6); regions not all visible, dorsal surface slightly convex; surface pitted, anterolateral regions slightly rugose (Fig. 8 View Figure 8 ). Frontal margin sinuous, deflexed (Fig. 8 View Figure 8 ). Epigastric cristae and postorbital cristae confluent, sharp; bifurcated shallow groove between epigastric cristae (Fig. 8 View Figure 8 ). Branchial regions not swollen (Fig. 8 View Figure 8 ). Cervical groove obvious (Fig. 8 View Figure 8 ). Mesogastric region flat (Fig. 8 View Figure 8 ). External orbital angle broadly triangular, outer margin slightly convex, almost confluent with anterolateral margin (Figs 8 View Figure 8 , 9 A View Figure 9 ). Epibranchial tooth granular, indistinct (Figs 8 View Figure 8 , 9 A View Figure 9 ). Anterolateral margin lined with 10–14 granules; posterolateral margin posteriorly convergent (Fig. 8 View Figure 8 ); posterolateral with weak striae (Fig. 8 View Figure 8 ). Orbits regular; supraorbital margins cristate, infraorbital margins lined with fused granules (Fig. 9 A View Figure 9 ). Eyes normal (Figs 8 View Figure 8 , 9 A View Figure 9 ). Sub-orbital, pterygostomial and sub-hepatic regions generally smooth, pitted (Fig. 9 A View Figure 9 ). Antennules large, folded within broad fossae; antennae very short (Fig. 9 A View Figure 9 ). Median lobe of epistome buccal margin broadly triangular, lateral margins straight (Fig. 9 A View Figure 9 ).

Maxilliped 3 merus subtrapezoidal, with slight median depression, width ~ 1.3 × length; ischium subtrapezoidal with very shallow median sulcus, distomesial margin rounded, width ~ 0.7 × length. Exopod reaching proximal one-third of merus; flagellum short (Fig. 10 A View Figure 10 ).

Chelipeds (pereiopod 1) subequal (Fig. 10 F – I View Figure 10 ). Merus trigonal in cross section, surfaces generally smooth; outer dorsal margin slightly crenulated, inner and ventral margin lined with large granules (Figs 8 View Figure 8 , 9 A View Figure 9 ). Carpus dorsal surface slightly rugose, with small blunt spine at inner-distal angle, spinule at base (Fig. 8 View Figure 8 ). Major cheliped palm length ~ 1.4–1.5 × height in males (n = 3), 1.4 × height in females (n = 2); dactylus 0.9 × palm length in males (n = 3), 0.8–0.9 × palm length in females (n = 2) (Fig. 10 F – I View Figure 10 ). Palm surface pitted, occlusal margin of fingers with 9–13 irregular blunt teeth, with very small gape when closed (Fig. 10 F – I View Figure 10 ).

Ambulatory legs slender (pereiopods 2–5), with only very short setae on margins (Fig. 8 View Figure 8 ). Pereiopod 3 merus 0.7 × CL in both sexes (n = 5, Fig. 8 View Figure 8 ). Pereiopod 5 propodus length 1.7–2.0 × height in males (n = 3), 1.8–1.9 × height in females (n = 2), longer than dactylus (Fig. 8 View Figure 8 ).

Male thoracic sternum generally smooth, sparsely pitted; sternites 1–4 width ~ 1.9 × length; sternites 1, 2 fused to form broad triangle; fused sternites 1, 2 demarcated from sternite 3 by slightly sinuous sulcus; sternites 3, 4 fused with distinct sulcus (Fig. 9 B View Figure 9 ). Male sterno-pleonal cavity reaching anteriorly slightly beyond mid-length of cheliped coxa (Fig. 9 B View Figure 9 ). Male pleonal locking tubercle positioned at mid-length of sternite 5 (Fig. 9 D View Figure 9 ). Female vulvae ovate, large, reaching suture of sternites 5 / 6, relatively widely separated (Fig. 9 F View Figure 9 ).

Male pleon large, broadly triangular; somites 3–6 progressively narrower; somite 6 width approximately 2.4 × length; telson width 1.8 × length; lateral margins almost straight, apex rounded (Fig. 6 C View Figure 6 ). Female pleon sub-ovate (Fig. 9 E View Figure 9 ).

G 1 large, sinuous, tip exceeding suture between thoracic sternites 4 / 5 in situ (Fig. 9 D View Figure 9 ); subterminal segment length ~ 2.7 × length of terminal segment (Fig. 10 C – E View Figure 10 ). Subterminal segment thick, outer margin strongly concave, distal end slanted with outer-distal section highest; terminal segment short, both lateral margins slightly convex, bifurcated with one point being opening tip and other being smaller projection on outer margin, both pointing upwards (Figs 10 C – E View Figure 10 , 11 C, D View Figure 11 ). G 2 subterminal segment thick, slightly bent outwards distally, flagelliform terminal segment thin, ~ 2.3 × length of subterminal segment (Fig. 10 B View Figure 10 ).

Colour in life.

Generally camouflaged in light mottled brown overall (Fig. 13 D View Figure 13 ).

Habitat.

This is a typical aquatic hill stream species that can be found residing under rocks in the shallows of the hillstream. The sympatric Eurusamon guangdongense is also aquatic but can grow to a much larger size and mature individuals occupy the deeper areas of the hillstream.

Distribution.

Yangdong County, Yangjiang City, Guangdong Province, China.

Etymology.

This species is named after the type locality, Yangdong County.

Remarks.

This new species is closest to Megapleonum ehuangzhang and especially M. shenzhen in terms of carapace and gonopodal morphology, and the three are no doubt closely related. Megapleonum yangdongense sp. nov., however, can be distinguished from the other two by its prong-shaped G 1 terminal segment (vs folded terminal segment in M. ehuangzhang, Huang et al. 2018 : fig. 3 C, and goose-head-shaped terminal segment in M. shenzhen, Huang and Mao 2021 : fig. 3 C – E). Otherwise, it can further be separated from the two aforementioned congeners in having a slightly narrower male abdominal somite 6, with the width ~ 2.4 × length (vs 2.6 × in both M. ehuangzhang and M. shenzhen, Huang et al. 2018 ; Huang and Mao 2021). More detailed comparisons can be found in Table 1 View Table 1 . Interspecific variation of the G 1 is minimal, with the terminal segment slightly varying in size and the outer projection of the terminal segment slightly varying in sharpness and angle (Fig. 10 C – E View Figure 10 ).