Camptoplax ahmar, Ng & Anker, 2024

Ng, Peter K. L. & Anker, Arthur, 2024, Camptoplax ahmar sp. nov., a new pilumnid crab (Crustacea: Brachyura) from the Red Sea, Zootaxa 5496 (1), pp. 119-126 : 120-126

publication ID	https://doi.org/ 10.11646/zootaxa.5496.1.7
publication LSID	lsid:zoobank.org:pub:A5069C57-6179-41EE-9134-B3D4F8C7A222
DOI	https://doi.org/10.5281/zenodo.13331084
persistent identifier	https://treatment.plazi.org/id/8509878D-9B0C-FF87-C8A9-FDF71286FD56
treatment provided by	Plazi
scientific name	Camptoplax ahmar
status	sp. nov.

Treatment

Camptoplax ahmar sp. nov.

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 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). GoogleMaps

Diagnosis. Frontal margin prominently projecting anteriorly, margin clearly beyond base of orbit ( Figs. 1A View FIGURE 1 , 2A–D View FIGURE 2 ); male chela relatively elongate, fingers shorter than palm ( Figs. 1A–C View FIGURE 1 , 2A View FIGURE 2 , 3C View FIGURE 3 , 4A, B View FIGURE 4 ); 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 View FIGURE 1 , 2A View FIGURE 2 , 4C, D View FIGURE 4 ); G1 sinuous, elongate, relatively slender; distal part gently curved, sharply tapering to rounded tip ( Fig. 5B–D View FIGURE 5 ).

Description. Carapace subhexagonal ( Figs. 1A View FIGURE 1 , 2A, B View FIGURE 2 ), 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 View FIGURE 1 , 2A, B, D View FIGURE 2 ). Median part lowest; branchial regions slightly higher in frontal view ( Figs. 1C View FIGURE 1 , 2D View FIGURE 2 ). 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 View FIGURE 2 ). Posterolateral margin almost straight; lateral surfaces with low, oblique striae, distinctly converging to posterior carapace margin ( Figs. 1A View FIGURE 1 , 2A, B View FIGURE 2 ). 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 View FIGURE 1 , 2B–E View FIGURE 2 ). Supraorbital margin short, concave, lined with granules, without obvious notch or fissure ( Fig. 2B, C View FIGURE 2 ). Suborbital margin short, gently concave, lined with rounded granules; suborbital tooth low, rounded, eroded ( Figs. 2E View FIGURE 2 , 3A View FIGURE 3 ). Suborbital, subhepatic and ptreygostomial regions rugose ( Figs. 2D View FIGURE 2 , 3C View FIGURE 3 ). Antennular fossa relatively broad, subrectangular; antennules folding laterally ( Figs. 2D, E View FIGURE 2 , 3A, C View FIGURE 3 ). Basal antennal article subrectangular, lodged into orbital hiatus; flagellum just entering orbit ( Figs. 2D, E View FIGURE 2 , 3A View FIGURE 3 ). Orbit short; orbital peduncle short, stout; cornea well developed ( Figs. 2B–D View FIGURE 2 , 3A View FIGURE 3 ). 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 View FIGURE 2 , 3A View FIGURE 3 ). 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 View FIGURE 2 , 3B, C View FIGURE 3 ).

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 View FIGURE 1 , 3C–E View FIGURE 3 ). 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 View FIGURE 1 , 2A View FIGURE 2 , 3C View FIGURE 3 , 4A, B View FIGURE 4 ). Margins of basis and ischium entire ( Figs. 1B View FIGURE 1 , 3C View FIGURE 3 ). 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 View FIGURE 1 , 3C View FIGURE 3 ). Carpus surface slightly eroded, with smooth, sharp, triangular tooth on inner distal angle; outer angle slightly produced ( Figs. 1A View FIGURE 1 , 2A View FIGURE 2 , 4B View FIGURE 4 ). Right chela relatively more swollen than minor chela, otherwise similar in form ( Figs. 1 View FIGURE 1 , 4A View FIGURE 4 ). 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 View FIGURE 1 , 2A View FIGURE 2 , 3C View FIGURE 3 , 4A, B View FIGURE 4 ).

P2–P5 relatively short, P3 longest, P5 shortest, surfaces covered with short, felt-like setae obscuring surface and margins ( Figs. 1A View FIGURE 1 , 2A View FIGURE 2 , 3C View FIGURE 3 ). 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 View FIGURE 1 , 2A View FIGURE 2 , 3C View FIGURE 3 , 4C, D View FIGURE 4 ).

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 View FIGURE 1 , 3C, D View FIGURE 3 , 5A View FIGURE 5 ).

G1 sinuous, elongate, relatively slender; distal part gently curved, sharply tapering to rounded tip, margins lined with stiff spines ( Fig. 5B–D View FIGURE 5 ). G2 short, sigmoid, distal part spatuliform, with short flagellum ( Fig. 5E View FIGURE 5 ).

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 View FIGURE 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 View FIGURE 1 , 2D View FIGURE 2 ) (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 View FIGURE 2 ) (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 View FIGURE 3 ) (versus more quadrate in C. coppingeri ; cf. Davie 1993: fig. 1B); the chelae of C. ahmar sp. nov. are proportionately longer ( Fig. 4A View FIGURE 4 ) (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 View FIGURE 4 ) 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 View FIGURE 4 ) (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 View FIGURE 5 ), with the distal curved part also being proportionately longer ( Fig. 5B–D View FIGURE 5 ) (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)