Camptoplax ahmar sp. nov., a new pilumnid crab (Crustacea: Brachyura) from the Red Sea Author Ng, Peter K. L. Lee Kong Chian Natural History Museum, Faculty of Science, National University of Singapore, 2 Conservatory Drive, Singapore 117377, Singapore Author Anker, Arthur Universidade Federal de Pelotas (UFPEL), Departamento de Ecologia, Zoologia e Genética, Instituto de Biologia, Campus Universitário Capão do Leão, RS, 96010 - 610, Brazil & Biological and Environmental Science & Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia text Zootaxa 2024 2024-08-16 5496 1 119 126 http://dx.doi.org/10.11646/zootaxa.5496.1.7 journal article 10.11646/zootaxa.5496.1.7 1175-5326 13331098 A5069C57-6179-41EE-9134-B3D4F8C7A222 Camptoplax ahmar sp. nov. ( Figs. 1–5 ) Material examined . Holotype : male (9.7 × 8.0 mm) ( FLMNH UF 72875 ), Saudi Arabia , Red Sea coast, Thuwal , King Abdullah University of Science & Technology ( KAUST ), near King Abdullah Monument , 22°20’26.2”N 39°05’15.1”E , shallow reef flat with some seagrass and coral rubble, depth less than 1 m , in burrow of unknown host, suction (yabby) pump, coll. A. Anker & A. Assayie , 29 December 2022 (fcn AA-22-447). Diagnosis . Frontal margin prominently projecting anteriorly, margin clearly beyond base of orbit ( Figs. 1A , 2A–D ); male chela relatively elongate, fingers shorter than palm ( Figs. 1A–C , 2A , 3C , 4A, B ); P4 merus length 2.98 times width; P5 merus length 2.94 times width; P2–P4 propodus elongate, P4 propodus length 2.63 times width; P5 propodus short, length 1.80 times width; P4 dactylus long, falciform, length 1.07 times width; P5 dactylus short, length 0.94 times width ( Figs. 1A , 2A , 4C, D ); G1 sinuous, elongate, relatively slender; distal part gently curved, sharply tapering to rounded tip ( Fig. 5B–D ). Description . Carapace subhexagonal ( Figs. 1A , 2A, B ), wider than long. Dorsal surface uneven, covered with flattened granules and rugosities, appearing finely eroded with pits; entire surface covered with dense, felt-like setae, and with 3 transverse swellings spanning entire carapace width: one at level of protogastric region stretching to epibranchial region, one across metagastric region reaching across mesobranchial region, and one across cardiac region stretching across metabranchial region, also forming 3 broad, shallow transverse depressions, anterior one being shallowest, with median parts relatively higher; gastro-cardiac grooves visible ( Figs. 1A, C , 2A, B, D ). Median part lowest; branchial regions slightly higher in frontal view ( Figs. 1C , 2D ). Anterolateral margin convex, with 4 low teeth or lobes; first tooth (= external orbital tooth) very low, wide, almost straight, with granulated margin; second tooth dentiform, low; third tooth dentiform, low, with rounded tip; last tooth at junction of antero- and posterolateral margins very low, lobiform, broadly rounded ( Figs. 2A–D ). Posterolateral margin almost straight; lateral surfaces with low, oblique striae, distinctly converging to posterior carapace margin ( Figs. 1A , 2A, B ). Frontal margin prominently projecting anteriorly; margin clearly beyond base of orbit; lateral lobe small, barely visible in dorsal view, separated by shallow groove ( Figs. 1A , 2B–E ). Supraorbital margin short, concave, lined with granules, without obvious notch or fissure ( Fig. 2B, C ). Suborbital margin short, gently concave, lined with rounded granules; suborbital tooth low, rounded, eroded ( Figs. 2E , 3A ). Suborbital, subhepatic and ptreygostomial regions rugose ( Figs. 2D , 3C ). Antennular fossa relatively broad, subrectangular; antennules folding laterally ( Figs. 2D, E , 3A, C ). Basal antennal article subrectangular, lodged into orbital hiatus; flagellum just entering orbit ( Figs. 2D, E , 3A ). Orbit short; orbital peduncle short, stout; cornea well developed ( Figs. 2B–D , 3A ). Epistome distinct, posterior margin with broadly triangular median lobe, with shallow median fissure, separated from lateral parts by wide concavities, shallow fissure present slightly mesial to concavities ( Figs. 2D, E , 3A ). Endostome with low, oblique ridge. Third maxilliped covered with short setae, latter not concealing margin; ischium rectangular, with shallow median oblique depression; inner margin serrate; merus quadrate, anteroexternal angle distinct, produced but not obviously auriculiform; exopod relatively stout, reaching to distal edge of merus, with long flagellum ( Figs. 2D , 3B, C ). FIGURE 1. Camptoplax ahmar sp. nov. , holotype, male (9.7 × 8.0 mm) from Thuwal, Saudi Arabia, FLMNH UF 72875, crab alive in dorsal (A), ventral (B) and frontal (C) views (right P2 missing). Photographs by AA. FIGURE 2. Camptoplax ahmar sp. nov. , holotype, male (9.7 × 8.0 mm) from Thuwal, Saudi Arabia, FLMNH UF 72875; A, habitus, dorsal view (right P2 missing); B, carapace, dorsal view; C, right side of carapace, showing orbits and front, dorsal view; D, cephalothorax, frontal view; E, antennules, antenna, orbit, suborbital region and epistome, frontal view. FIGURE 3. Camptoplax ahmar sp. nov. , holotype, male (9.7 × 8.0 mm) from Thuwal, Saudi Arabia, FLMNH UF 72875; A, antennules, antenna, orbit, suborbital region and epistome (denuded), frontal view; B, right third maxilliped (denuded), outer view; C, cephalothorax, anteroventral view; D, posterior thoracic sternum and pleonal somites 1–5, showing exposed sternite 8 (denuded), ventral view; E, anterior thoracic sternum and sternopleonal cavity, showing right G1 (denuded) in situ , ventral view. FIGURE 4. Camptoplax ahmar sp. nov. , holotype, male (9.7 × 8.0 mm) from Thuwal, Saudi Arabia, FLMNH UF 72875; A, right and left chelae, outer view; B, right cheliped (partially denuded), dorsal view; C, right P4 (partially denuded), dorsal view; D, right P5 (partially denuded), dorsal view. Thoracic sternites densely covered with very short setae; sternites 1 and 2 completely fused, their lateral margins sinuous; suture between sternites 2 and 3 gently convex towards buccal cavity; sternites 3 and 4 demarcated by shallow, oblique groove; sternopleonal cavity deep, reaching to imaginary line connecting proximo-distal edge of coxae of chelipeds; tubercle of pleonal locking mechanism round, on proximal third of sternite 5; sternite 8 visible as subrectangular plate when pleon closed ( Figs. 1B , 3C–E ). Penis relatively short, exiting from condyle of P5 coxa. Chelipeds relatively short, subsymmetrical in shape, subequal in size, right slightly larger; outer surfaces covered with flattened rounded granules and short, felt-like setae partially obscuring margins and surface, however, leaving most granules visible; inner surface of carpus and chela smooth, that of merus rugose ( Figs. 1A , 2A , 3C , 4A, B ). Margins of basis and ischium entire ( Figs. 1B , 3C ). Merus short, with uneven but not serrate margins; distal angle of dorsal margin with low, rounded tubercle; subdistal edge of extensor margin with low tooth ( Figs. 1A, B , 3C ). Carpus surface slightly eroded, with smooth, sharp, triangular tooth on inner distal angle; outer angle slightly produced ( Figs. 1A , 2A , 4B ). Right chela relatively more swollen than minor chela, otherwise similar in form ( Figs. 1 , 4A ). Chela relatively elongate, fingers shorter than palm; outer surface with flattened granules covering most of surface of pollex except for distal-most part, covering proximal third of dactylus, with 2 low, uneven, rugose, longitudinal ridges; dorsal margin forming wide, low crest; inner surface longitudinally concave; cutting edges of fingers with low, rounded teeth ( Figs. 1 , 2A , 3C , 4A, B ). P2–P5 relatively short, P3 longest, P5 shortest, surfaces covered with short, felt-like setae obscuring surface and margins ( Figs. 1A , 2A , 3C ). Merus with extensor and flexor margins smooth, gently cristate, unarmed; P4 merus length 2.98 times width; P5 merus length 2.94 times width; carpus with low, submarginal crest and adjacent shallow furrow; propodus elongate, laterally flattened, with low, submarginal ridge; P2–P4 propodus elongate, P4 propodus length 2.63 times width; P5 propodus short, ovate, length 1.80 times width; dactylo-propodal lock visible; P2–P4 dactylus long, falciform, length 1.07 times width; P5 dactylus short, straight, length 0.94 times width ( Figs. 1A , 2A , 3C , 4C, D ). Pleon triangular; somite 1 wide, subrectangular, reaching to base of P5 coxae; somite 2 transversely ovate, narrower than somite 1; somite 3 trapezoidal, as wide as somite 1; somites 4–6 trapezoidal, gradually decreasing in width; telson triangular, as long as somite 6, with convex lateral margins and proximal margin slightly wider than somite 6 ( Figs. 1B , 3C, D , 5A ). G1 sinuous, elongate, relatively slender; distal part gently curved, sharply tapering to rounded tip, margins lined with stiff spines ( Fig. 5B–D ). G2 short, sigmoid, distal part spatuliform, with short flagellum ( Fig. 5E ). FIGURE 5. Camptoplax ahmar sp. nov. , holotype, male (9.7 × 8.0 mm) from Thuwal, Saudi Arabia, FLMNH UF 72875; A, pleon; B, left G1, ventral view; C, distal part of left G1, ventral view; D, distal part of left G1, dorsal view; E, left G2, ventral view. Scales: A = 1.0 mm; B, E = 0.5 mm; C, D = 0.2 mm. Colour in life . Overall straw yellowish with some slightly darker, pale brown areas; scarce reddish dots and small reddish patches present on some areas of dorsal and pterygostomian surface of carapace and extensor margins of P2–P5; posterior margin of epistome with 2 conspicuous red dots on median section and 2 red patches laterally ( Fig. 1 ). Etymology . The new species is named after the Red Sea, where the type locality is situated, using the Arabic word “ahmar ” (= red); used as a noun in apposition. Remarks . The new species and C. coppingeri are morphologically very similar, but compared to C. coppingeri , C. ahmar sp. nov. has the dorsal surface of the carapace gently concave medially in frontal view ( Figs. 1C , 2D ) (versus almost flat in frontal view in C. coppingeri , cf. Davie 1993 : fig. 1A); the front of C. ahmar sp. nov. is more prominently projecting anteriorly ( Fig. 2A, B ) (versus having the margin of the front level just above the orbit bases in C. coppingeri ; cf. Miers 1884 : pl. 24A; Davie 1993 : fig. 2); the third maxilliped ischium of C. ahmar sp. nov. is proportionately longer and more rectangular ( Fig. 3B ) (versus more quadrate in C. coppingeri ; cf. Davie 1993 : fig. 1B); the chelae of C. ahmar sp. nov. are proportionately longer ( Fig. 4A ) (versus distinctly shorter in C. coppingeri ; cf. Davie 1993 : fig. 1E); the P4 and P5 meri are slightly longer (length to width ratio 2.98 and 2.94, respectively; Fig. 4C, D ) in the new species (versus slightly shorter, length to width ratio 2.93 and 2.67, respectively, in C. coppingeri ; cf. Davie 1993 : figs. 1C, D, 2); the P4 propodus and dactylus of C. ahmar sp. nov. are longer (propodus length to width ratio 2.63, length of dactylus 1.07 times propodus length; Fig. 4C ) (versus distinctly shorter, propodus length to width ratio 2.41, length of dactylus 0.92 times propodus length, in C. coppingeri ; cf. Davie 1993 : fig. 1D); and the distal half of the G1 of C. ahmar sp. nov. is proportionately shorter and stouter ( Fig. 5B–D ), with the distal curved part also being proportionately longer ( Fig. 5B–D ) (versus the distal half of the G1 being shorter and more slender and with a shorter distal curved part, in its congener; cf. Davie 1993 : fig. 1F, G). The dorsal surface of C. ahmar sp. nov. is distinctly more depressed medially than that of C. coppingeri , and this seems to be independent of the angle it is viewed from. The discriminating characters of the P2–P5 are clearly discernible, although their validity need to be ascertained in the future with more specimens collected. Nevertheless, these differences do not seem to be age-related since all examined specimens are in the same size range. The type specimen of C. ahmar sp. nov. was extracted from a burrow of unknown host (presumably not its own burrow), using a suction (yabby) pump in very shallow water (depth less than 1 m ). Whether burrows are the typical habitat of the Red Sea species remains uncertain. The type specimens of C. coppingeri were dredged from a depth of 12.8–16.5 m (Miers 1994: 240), while the specimen from the Chesterfield Islands was collected on a sandy substrate in a lagoon with coral reef setting, at a depth of 13.0– 16.5 m ( Davie 1993: 71 ). However, the northern Australian specimen was collected in deeper water, at a depth range of 49–52 m ( Takeda et al. 2022 )