Paranaxia keesingi, Hosie, Andrew M. & Hara, Ana, 2016

Hosie, Andrew M. & Hara, Ana, 2016, Description of a new species of brooding spider crab in the genus Paranaxia Rathbun, 1924 (Brachyura: Majoidea), from northern Australia and Indonesia, Zootaxa 4127 (1), pp. 121-134 : 126-130

Paranaxia keesingi sp. nov.

( Figs 2 , 3 E–H, 4E–H)

Paranaxia serpulifera— Rahayu & Ng 2000: 889; non Paranaxia serpulifera (Guérin, 1832, in Guérin-Méneville 1829 –1837)

Material examined. Holotype: WAM C39266, 1 male, 139.2 × 102.3 mm, off Pelsaert Island, Abrolhos Islands, 28°47.33`S 113°59.13`E, 36–37.5 m, 26 Apr. 2007, A.S. Sampey coll.

Allotype: WAM C41266, 1 ovigerous female, 78.2 × 58.0 mm, Admiralty Gulf, Kimberley, 14°16`S 125°52`E, 1968.

Paratypes: WAM C10971, 1 male, 116.1 × 83.7 mm, 1 female with juveniles, 115.5 × 88.3 mm, Shark Bay, 25°25`S 113°35`E, 174 m, Aug. 1972. WAM C38294, 1 male, 112.7 × 84.3 mm, Point Cloates, 23°39`S 113°11`E, 7 Oct. 1963. WAM C59958, 1 male 84.6 × 62.5 mm, Round Island, Passage Islands, Pilbara, 20°55`49"S 115°51`36"E, 14.6 to 16.2 m, 21 Jun. 2013, E. Morello, G. Fry, M. Miller, D. Thomson, & D. Bearham coll. WAM C66922, 1 female, 33.47 × 17.6 mm, N of Lamarck Island, Kimberley, Stn SOL52/WA045, 14°43.248`S 125°02.378`E, 32.7-32.8 m, Dec. 2015, coll. G.A. Gomez & J.A. Ritchie. QM W9950, 1 female, 99.8 × 77.5 mm, 45 kms NE Cooktown, 15°6'5"S, 145°29'4"E, 34.7 m, Oct. 1979. QM W12653, 1 male, 98.6 × 68.0 mm, SW Yorke Island, Torres Straits, 9°44'S, 143°25'E, 35 m, 23 Feb. 1982.

Other material: WESTERN AUSTRALIA: WAM C11271, 1 female, 71.2 × 49.6 mm, Shark Bay, 25°25`S 113°35`E, Aug. 1965, A. Mackenzie coll. WAM C11274, 1 female, 71.2 × 49.6 mm, Ashburton Area, Onslow, 21°38`S 115°07`E, 1 Oct 1964, W. & W. Poole coll. WAM C13661, 1 male, 88.1 × 68.4 mm, Broome, 17°58`00"S 122°14`00"E, 1965, R. Risbey coll. WAM C13748, 1 male, 85.7 mm, NE Of Montebello Islands, 20°16`00"S 115°47`00"E, 55–57 m, 5 Dec. 1979, S.M. Slack-Smith & L.M. Marsh coll. WAM C13749, 1 male, 121.6 × 88.0 mm, NW Of Shark Bay, 23°34`00"S 113°10`00"E, 151 m, 30 Jun. 1981. WAM C15742, 1 male, 46.2 × 35.7 mm, 1 female, 70.0 × 50.7 mm, Denham, Sep. 1963, FRV Bluefin. WAM C39201, 1 female, 86.2 × 62.5 mm, off Pelsaert Island, Abrolhos Islands, 28°44.55`S 113°59`E, 36 m, 26 Apr. 2007, A. Sampey coll. WAM C42080, 1 male, 24.1 × 16.1 mm, north side of Jar Island, Kimberley, 14°08.48`S 126°14.56`E, 0 m, 23 Nov. 1995, J. Short coll. WAM C53543, 1 male, 37.8 × 25.7 mm, east of Lesueur Island, Kimberley, 72 m, 12 Jun. 2013, A.M. Hosie & A. Hara coll. WAM C54862, 1 male, 126.0 × 87.4 mm, Shark Bay, 25°40`S 113°42`E, Jul. 1963, W. & W. Poole coll, FRV Bluefin. WAM C54872, 1 male, 84.2 × 66.2 mm, Shark Bay, 25°40`S 113°42`E, Jul. 1963, W. & W. Poole coll, FRV Bluefin. WAM C55213, 1 male, 60.4 × 39.3 mm, Exmouth Gulf, 22°07`S 114°17`E, 11 Mar. 2004. WAM C55214, 1 male, 98.8 × 77.3 mm, Denham Sound, 25°46`S 113°15`E, 15 Mar. 2004. WAM C55436, 1 male, 35.6 × 24.2 mm, Shark Bay, 10/03/2004, S. Morrison coll.

QUEENSLAND: QM W16108, 1 male, 43.9 × 30.6 mm, near Stephens Island, Torres Strait, 9°24'S 143°24'E, 22m, 28 Sep. 1988. QM W16539, 1 male, 54.2 × 39.3 mm, near Warrior Reefs, Torres Strait. QM W43175, 1 female, 67.5 × 47.7 mm, Great Barrier Reef, site 10614376, 10°36'36"S 143°45'36"E, 10 Jan. 2004. QM W43176, 1 male, 80.6 × 57.6 mm, Great Barrier Reef, site 1968, 10°54'18"S 143°3'18"E, 25m, 26 Sep. 2004. QM W43177, 1 male, 99.9 × 77.7 mm, Great Barrier Reef, site 2479 10°58'30"S 143°15'54"E, 28 m, 26 Sep. 2004.QM W52799, 1 female, 75.8x58.0 mm, Northern Prawn Survey, Stn 98, 13°44'18"S 143°48'E, 18 m, 28 Sep. 1979. QM W52800, 1 female, 28.5 × 19.9 mm, Northern Prawn Survey. Stn 113, 13°26'18"S 143°19'42"E, 18 m, 24 Sep. 1979.

INDONESIA: ZRC 1999.1470, 1 male, 24.5 × 17.2 trawl, Arafura Sea, Papua, 8°37’S 138°18’ E, on mud, 10 Dec. 1967.

Diagnosis. Body, ambulatory legs completely covered in dense pubescence, hooked setae present on rostrum, preorbital spines, anterolateral carapace margins, dorsal tubercles, all ambulatory leg articles except dactyls. Male, female rostrum length 0.24–0.50 times CW. Subhepatic region unarmed. Pterygostomian region with sharp spine. Intestinal tubercle produced beyond posterior carapace margin. Sternal cavities prominent, medial cavity on sternite 3, 4 subcircular, posterior margin notched, longitudinally divided; 3 paired cavities on sternites 5. Chelipeds of mature males stout, length up to 0.7 times P2, merus extending to mid-point of rostrum, prominent posterodistal spine acute; propodus length up to 1.09 times CW. Pereiopods 2–5 slender, P2 dactyl 0.55–0.93 times CW.

Description. Holotype male. Carapace pyriform, PCL 1.36 (1.27–1.53) times CW, regions defined, densely covered in short pubescence; hooked setae present on tubercle apices, anterior branchial, hepatic margins. Rostral horns parallel, distally bifid, 0.39 (0.24–0.50) times CW; tufts of hooked setae on lateral, dorsal, mesial surfaces. Orbits closed dorsally, ventrally, preorbital angle produced into large anterodorsally directed spine with hooked setae; postorbital lobe anteriorly cupped; dorsal orbital hiatus as narrow fissure.

Gastric region elevated, slightly higher than other regions; 13 small tubercles distributed in anterior gastric region; apex with 3 larger, blunt tubercles. Hepatic region inflated, unarmed. Pterygostomian region with sharp stout spine directly ventral to subhepatic region, not visible in dorsal view. Branchial region inflated with 2 low mesial tubercles; lateral margin with large laterally directed spine (slightly curved) above pereiopod 3, apex rounded. Cardiac region elevated, apex bluntly rounded. Intestinal tubercle large, apex rounded, protruding beyond posterior margin of carapace.

Eyestalks sparsely setose anteriorly, cornea terminal, retractable into orbit.

Antenna basal article laterally expanded to form suborbital floor; flagellum inserted ventral to rostrum, not visible dorsally.

Maxilliped 3 with dense pubescence, thicker, longer along borders of articles; ischium narrower than merus, mesial margin dentate, lateral margin approximately 0.7 mesial margin length, outer surface with shallow longitudinal depression; merus subtriangular, anterolateral angle produced.

Chelipeds relatively stout, length 2.08 (1.90–2.08) CW, 0.67 (0.49–0.70) times P2; merus 0.65 (0.62–0.65) CW extending to midway along rostrum, with blunt medial dorsal tubercle, acute posterodistal spine; carpus smooth about as long as dactyl; propodus length 2.42 (2.42–3.95) height, 1.05 (0.56–1.09) times CW; smooth; dactyl with prominent tooth in gape, cutting margins of fingers crenulate.

Ambulatory legs slender, unarmed, covered in dense pubescence except at distal extremities of dactyls; hooked setae present dorsally on all articles except dactyls. P2 3.10 (2.72–3.6) CW; pereiopod 3 2.09 (2.03–2.29) CW; pereiopod 4 1.53 (1.50–1.83) CW; pereiopod 5 1.35 (1.28– 1.1.48) CW. Dactyls evenly curved, elongate; P2 dactyl 0.68 (0.62–0.81) CW, unarmed on ventral surface.

Sternum with series of prominent cavities surrounding pleon, each cavity placed across junction sternal segments, cavity on sternite 3, 4 subcircular, deep, longitudinally divided, posterior margin notched; 10 cavities present adjacent to articulation with each pereiopods, sternite 4, 8 cavities smallest; sternite 5–7 cavities transverse, sternite 5 cavity laterally divided into posterior, anterior lobes. Pleonal-locking tubercles prominent, on sternite 5 near suture with sternite 4.

Pleon with 6 free somites plus telson, widest at somites 2, 3, somite 6 lateral margins convex, width 1.45 times wider than long, wider than somite 5; telson triangular, width twice length, apex rounded. Raised ridged running length of pleon, all pleonal somites with transverse ridge, paired lateral cavities present at junctions of each somite.

Gonopod 1 slightly curved laterally, curvature lessening distally tapering distally into acute point, aperture subapical, basally with conspicuously short setae on lateral margins. Gonopod 2 stout, curved laterally, apex inflated spatulate, with scattered stout setae subapically. Penis coxal emerging from P5.

Allotype female. Surface details of carapace and pereiopods 2–5 same as for males. Chelipeds much shorter, more slender than holotype male, length 1.33 CW; merus 0.47 CW, with posterodistal spine; propodus length 3.3 (3.01–3.41) height, 0.43 (0.53–0.83) CW. P2 2.67 (2.46–4.27) times CW, dactyl 0.59 (0.56–0.93) times CW. Sternal cavity on sternite 3, 4 same as male; lacking cavities on sternites 5–8. Pleon covering whole of sternum except sternites 1–3; broadest at segments 5, 6, telson short, broad width 3.0 length. Vulvae subcircular, positioned in anterior half of sternite 6 submedially, blocked internally by chitinous vulvar valve.

Etymology. This species is named after Dr. John Keesing of CSIRO Marine and Atmospheric Research, in recognition of his contribution and commitment to the knowledge of Western Australian biodiversity.

Distribution. Australia: Western Australia (south to the Abrolhos Islands), Queensland. Indonesia: Papua ( Rahayu & Ng, 2000). Depth: 18– 174 m.

Remarks. Paranaxia keesingi sp. nov. is clearly related to P. serpulifera , having shared characters such as the dense pubescence on the carapace and ambulatory legs, distally bifid rostral spines, structure of the orbits, epibranchial spines, and sternal cavities. Separation of the two species is well supported morphologically and is in congruence with the small molecular dataset presented. Both species grow to roughly the same size and to a minimum carapace length at maturity of approximately 100 mm and 85 mm for males and females, respectively. A comparison of morphological features distinguishing P. keesingi sp. nov. from P. serpulifera is presented in Table 2 and 3.

One female of P. keesingi sp. nov. was found carrying juveniles underneath the pleon, proving that this is also a brooding species. The juveniles showed the characteristic long slender legs of this species ( Fig. 4 E) and are easily distinguished from juveniles of P. serpulifera ( Fig. 4 A).

Photographs of one of the specimens (ZRC 1999.1470) collected by Rahayu and Ng (2000), from near the Papua coast of the Arafura Sea, show distinctive long slender legs and a sub circular sternal cavity and thus this record is herein referred to as belonging to P. keesingi sp. nov.

From the examined records it appears that P. serpulifera and P. keesingi sp. nov. can be found sympatrically, but are typically separated by depth. Paranaxia serpulifera is seemingly limited to the intertidal zone down to around 20 m, while P. keesingi sp. nov. has been recorded from 18– 174 m.

Figures

FIGURE 2. Paranaxia keesingi sp. nov. A – D, holotype WAM C 39266 male; A, whole crab, dorsal view; B, carapace, lateral view; C, sternum and pleon, half denuded; D, male right cheliped, ventral view; E – G, allotype WAM C 41266 female, pleon; E, whole crab, dorsal view; F, pleon ventral view; G, left cheliped, ventral view. Scale bars: A – C, E, F, 20 mm; D, G 10 mm.

FIGURE 4. Gonopods. A – D, Paranaxia serpulifera (Guérin, 1832, in Guérin-Méneville 1829 – 1837), WAM C 55210. A, male right G 1, B, right G 1 distal portion, C, right G 2, D, G 2 distal portion. E – H, Paranaxia keesingi sp. nov., holotype WAM C 39266, E, right G 1; F, G 1 distal portion; G, right G 2; H, G 2 distal portion. Scale bars: A, C, E, G, 2 mm; B, D, F, H, 0.5 mm.

FIGURE 3. A – D, Paranaxia serpulifera (Guérin, 1832, in Guérin-Méneville 1829 – 1837). A, early stage crab, removed from under pleon of WAM C 41266; B – D, WAM C 56218 male; B, carapace dorsal view; C, carapace, lateral view; D, right chela, lateral view; E – H, Paranaxia keesingi sp. nov.; E, early stage crab, removed from under pleon of paratype WAM C 10971; F – H, paratype WAM C 38294 male; F, carapace dorsal view; G, carapace, lateral view; H, right chela, lateral view. Scale bars: A & E, 5 mm; B – D, F – H, 20 mm.