Megapleonum ferrumequinum, 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.15791870
persistent identifier	https://treatment.plazi.org/id/7FB5A7F2-3BF5-5961-9415-E29FCBFBB8C3
treatment provided by	ZooKeys by Pensoft
scientific name	Megapleonum ferrumequinum
status	sp. nov.

Treatment

Megapleonum ferrumequinum sp. nov.

Figs 3 View Figure 3 , 4 View Figure 4 , 13 A View Figure 13

Type material.

Holotype: • SYSBM 002143 , male (16.6 × 13.1 mm), Datianding , Dawuling Nature Reserve, Maoming City, Guangdong Province, China, 22.29°N, 111.22°E, dirt road near the summit at night, coll. Jian Wang, June 2018. GoogleMaps

Diagnosis.

Carapace broader than long, dorsal surface convex, lateral margins covered in dense setae; postorbital, epigastric cristae weak, almost confluent (Fig. 3 A View Figure 3 ). Maxilliped 3 merus width ~ 1.3 × length; ischium width ~ 0.7 × length; exopod reaching slightly beyond anterior edge of ischium, without flagellum (Fig. 4 A View Figure 4 ). Ambulatory legs densely setose; pereiopod dactylus shorter than propodus (Fig. 3 A View Figure 3 ). Male anterior thoracic sternum very broad, width ~ 1.9 × length (Fig. 3 C View Figure 3 ). Male pleon large, sublinguiform, pleonite 6 width ~ 2.5 × length; telson width ~ 1.7 × length (Fig. 3 D View Figure 3 ). G 1 large, slightly sinuous, tip exceeding suture between thoracic sternites 4 / 5 in situ (Fig. 3 E View Figure 3 ); subterminal segment length ~ 2.5 × length of terminal segment (Fig. 4 C View Figure 4 ). Subterminal segment outer margin slightly concave, outer distal margin bulging; terminal segment curved inwards, tip pointed upwards in dissected view, connected to a large mesoanterior-facing horseshoe shaped structure, large thick proximal pad on dorsal side (Fig. 4 C, F, G View Figure 4 ). G 2 subterminal segment tapering, slightly bent outwards distally, flagelliform terminal segment thick, ~ 1.6 × length of subterminal segment, apex blunt (Fig. 4 B View Figure 4 ).

Description of male holotype.

Carapace broader than long, ~ 1.3 × as wide as long; regions not pronounced, dorsal surface convex; surface finely pitted, dense setae at lateral margins (Fig. 3 A View Figure 3 ). Frontal margin almost straight, deflexed (Fig. 3 A, B View Figure 3 ). Epigastric cristae and postorbital cristae rugose, low, almost confluent; bifurcated shallow groove between epigastric cristae (Fig. 3 A View Figure 3 ). Branchial regions not swollen (Fig. 3 A, B View Figure 3 ). Cervical groove shallow, barely visible (Fig. 3 A View Figure 3 ). Mesogastric region flat (Fig. 3 A View Figure 3 ). External orbital angle broadly triangular, outer margin slightly convex, confluent with anterolateral margin (Fig. 3 A, B View Figure 3 ). Epibranchial tooth granular, indistinct (Fig. 3 A, B View Figure 3 ). Anterolateral margin lined with indistinct single or partially fused granules; posterolateral margin posteriorly convergent (Fig. 3 A View Figure 3 ); posterolateral surface smooth (Fig. 3 A View Figure 3 ). Orbits regular; supraorbital margins weakly cristate, infraorbital margins lined with fused granules (Fig. 3 B View Figure 3 ). Eyes normal (Fig. 3 A, B View Figure 3 ). Sub-orbital, pterygostomial and sub-hepatic regions generally smooth, pitted (Fig. 1 B View Figure 1 ). Antennules large, folded within broad fossae; antennae very short (Fig. 3 B View Figure 3 ). Median lobe of epistome buccal margin broadly triangular, lateral margins straight (Fig. 3 B View Figure 3 ).

Maxilliped 3 merus subtrapezoidal, with slight median depression, width ~ 1.4 × length; ischium subtrapezoidal with shallow median sulcus, distomesial margin rounded, width ~ 0.7 × length. Exopod reaching proximal one-third of merus; flagellum absent (Fig. 4 A View Figure 4 ).

Chelipeds (pereiopod 1) subequal (Fig. 4 D, E View Figure 4 ). Merus trigonal in cross section, surfaces generally smooth, margins lined with long setae; outer dorsal margin slightly crenulated margins slightly crenulated, inner and ventral margin lined with large granules (Fig. 3 A, B View Figure 3 ). Carpus dorsal surface slightly rugose, with large spike at inner-distal angle, spinule at base (Fig. 3 A View Figure 3 ). Major cheliped palm length ~ 1.5 × height; dactylus 0.7 × palm length (Fig. 2 D, E View Figure 2 ). Palm surface pitted, occlusal margin of fingers with 7–9 irregular blunt teeth, with small gape when closed (Fig. 2 D, E View Figure 2 ).

Ambulatory legs (pereiopods 2–5) covered with setae, especially dense on pereiopods 2–3 (Fig. 3 A View Figure 3 ). Pereiopod 3 merus 0.6 × CL (Fig. 3 A View Figure 3 ). Pereiopod 5 propodus length 1.7 × height, longer than dactylus (Fig. 3 A View Figure 3 ).

Male thoracic sternum generally smooth, pitted, setae at margins and sparsely on sternites; sternites 1–4 width ~ 1.9 × length; sternites 1, 2 fused to form broad triangle; fused sternites 1, 2 demarcated from sternite 3 by sinuous transverse sulcus, sulcus lined with setae; sternites 3, 4 fused without obvious demarcation (Fig. 3 C View Figure 3 ). Male sterno-pleonal cavity reaching anteriorly slightly beyond mid-length of cheliped coxa (Fig. 3 C View Figure 3 ). Male pleonal locking tubercle positioned slightly posterior to mid-length of sternite 5 (Fig. 3 E View Figure 3 ).

Male pleon large, sublinguiform; somites 3–6 progressively narrower; somite 6 width approximately 2.5 × length; telson width 1.7 × length; lateral margins almost straight, apex rounded (Fig. 3 D View Figure 3 ).

G 1 large, slightly sinuous, tip exceeding suture between thoracic sternites 4 / 5 in situ (Fig. 3 E View Figure 3 ); subterminal segment length ~ 2.5 × length of terminal segment (Fig. 4 C View Figure 4 ). Subterminal segment outer margin slightly concave, outer distal margin bulging; terminal segment curved inwards, tip pointed upwards in dissected view, connected to a large meso-anterior-facing horseshoe shaped structure, large thick proximal pad on dorsal side (Fig. 4 C, F, G View Figure 4 ). G 2 subterminal segment tapering, slightly bent outwards distally, flagelliform terminal segment thick, ~ 1.6 × length of subterminal segment, apex blunt (Fig. 4 B View Figure 4 ).

Colour in life.

Generally drab camouflage-brown all over (Fig. 13 A View Figure 13 ).

Habitat.

Typical habitat unknown. The only specimen collected was found at night on the side of a dirt road near the summit at approximately 1600 m above sea level. Multiple subsequent attempts to find this species in the same area failed to locate any more specimens with only Megapleonum wangjiani sp. nov. and Eurusamon guangdongense being found. The true habitat of this species remains elusive.

Distribution.

Dawuling Nature Reserve, Maoming City, Guangdong Province, China.

Etymology.

The species name is the Latin word ferrumequinum, meaning horseshoe. It alludes to the horseshoe-shaped structure on the G 1 terminal segment of this species. Used as a noun in apposition.

Remarks.

Megapleonum ferrumequinum sp. nov. is unique in its genus by its sublinguiform male abdomen (Fig. 3 D View Figure 3 , vs broadly triangular in all other congeners) and its peculiar G 1, which is only slightly sinuous (Fig. 4 C View Figure 4 , vs more strongly sinuous in all other congeners) with a horseshoe-shaped structure in the terminal segment (Fig. 4 F – H View Figure 4 , vs absent in all other congeners). In possessing dense setation on the carapace margins and ambulatory legs, M. ferrumequinum sp. nov. is most similar to M. falx sp. nov. (see remarks for M. falx sp. nov.). More detailed comparisons can be found in Table 1 View Table 1 .