Gopkittisak ngankeeae, Lasley Jr & Anker & Naruse, 2024

Lasley Jr, Robert M., Anker, Arthur & Naruse, Tohru, 2024, Two new species and a new record of infaunal crabs (Decapoda: Brachyura: Pinnotheridae and Varunidae) from Oman and Saudi Arabia, Zootaxa 5476 (1), pp. 207-229 : 221-226

Gopkittisak ngankeeae n. sp.

( Figs. 9–12 )

Type material. Holotype: FLMNH UF 65444 , male (8.0/4.4), BOMAN-12365, Oman, Sur , stn OM22-92 , 22.56821°N, 59.54071°E, coastal bay near lighthouse, intertidal sandflat in large bay, depth 0–1 m, suction pump, coll. G. Paulay et al., 12.02.2022 . Paratypes: FLMNH UF 65445 , 1 male (7.2/4.1), BOMAN-12366, same collection data as for holotype ; FLMNH UF 63410 , 1 male (5.3/3.4), BOMAN-10868, Oman, west of Muscat, Al-Sawadi Beach, stn OM22-73 A, 23.78195°N, 57.79168°E, large intertidal sandflat, depth 0–1 m, suction pump, coll. A. Anker et al., 02.02.2022 ; FLMNH UF 63407 , 1 ovig. female (6.9/3.7), BOMAN-10865, same collection data as for previous specimen ; FLMNH UF 63408 , 1 juvenile (4.2/2.5), BOMAN-10866, same collection data as for previous specimens ; FLMNH UF 63842 , 1 male (5.3/3.3), BOMAN-11237, Oman, Al Sifah, stn OM22- 74 , 23.448°N, 58.780°E, coll. G. Paulay et al., 04.02.2022 ; FLMNH UF 63579 , 1 male (7.9/4.2), 1 ovig. female (8.4/4.6), BOMAN-10078, Oman, Mirbat, near Roshan Resort, stn OM22-53 A, 16.97576°N, 54.69363°E, small shallow bay, near-shore sandflat near boat ramp, depth 0.5–1 m, suction pump, coll. A. Anker, 26.01.2022 ; FLMNH UF 63805 , 1 ovig. female (10.4/5.5), BOMAN-10077, same collection data as for previous specimen ; FLMNH UF 63578 , 1 ovig. female (10.0/5.3), BOMAN-10076, same collection data as for previous specimen ; FLMNH UF 63580 , 1 ovig. female (9.1/4.9), BOMAN-10079, same collection data as for previous specimen ; FLMNH UF 69024 , 1 female (cw/cl indet.), BOMAN-13785, Oman, Masirah , west (channel-side) coast, Ghab Beach, stn MASA-17, 20.254481°N, 58,62367°E, silty-sandy-muddy sandflat near large rocks and some corals, depth 0.5–1 m, suction pump, coll. A. Anker, 13.11.2022 ; FLMNH UF 69025 , 1 female (cw/cl indet.), BOMAN-13786, same collection data as for previous specimen ; FLMNH UF 69026 , 1 female (cw/cl indet.), BOMAN-13787, same collection data as for previous specimen .

Description. Males. Carapace ( Fig. 9A ) transversely ovate, 1.76–1.82 times wider than long, dorsally slightly convex both longitudinally and transversely, smooth, glabrous; anterolateral margin convex to angular junction with posterolateral margin; urogastric fossa indicated; posterior third of dorsal surface with transverse ridge, laterally angled diagonally to meet junction of antero- and posterolateral margins; additional ridge parallel to posterolateral margins present; margins rimmed, slightly granulated laterally, orbit and frontal rim not granulated. Front ( Fig. 9A– C ) slightly deflexed, as wide as orbit; frontal margin bilobed, lobes slightly convex; fronto-orbital margin slightly wider than posterior margin of carapace; external orbital angle obtuse, anteriorly directed; lateral infraorbital margin short, extending downwards from external orbital tooth; ventral margin of orbit demarcated by suborbital crista, extending laterally parallel to carapace margin to enlarged flange, followed by several lobes; region between carapace margin and extended suborbital crista concave; flange and lobes lined ventrally with row of setae; inner orbital tooth short, abutting basal antennal article. Epistome short, shallowly concave, with medial triangular projection on posterior margin.

Eyes ( Fig. 9A–C ) well developed; cornea as wide as eyestalk, well pigmented. Antennular peduncle ( Fig. 9B, C ) folding transversely; article 1 large. Antennal peduncle ( Fig. 9C ) dorsally directed; article 3 touching lateral frontal angle; flagellum entering orbital hiatus, reaching external orbital angle.

Mxp3 ( Figs. 9B, C , 10C ) narrow, left and right ischia and meri filling about two-thirds width of buccal cavity. Ischium subrectangular, longer than merus measured along medial axis, with deep, mesially ridged, longitudinal depression running parallel to mesial and proximal margins; ischio-meral articulation oblique. Merus subrectangular, with deep, mesially ridged, longitudinal depression running parallel to mesial margin. Carpus articulated along outer (lateral) half of distal margin of merus. Propodus articulated along distal margin of carpus, with long setae on extensor margin. Dactylus subtriangular, articulated along distal margin of propodus, longer than propodus, bearing row of long setae on extensor and flexor margins. Distal margin of exopod not reaching distal margin of merus, with long flagellum.

Chelipeds ( Fig. 9A, E, F ) subequal, smooth, almost completely glabrous. Ischium short, smooth. Merus long, narrow, more than twice as long as wide in dorsal view; anterior margin granular, proximally keeled, forming lobe, widening distally, with tuft of short setae near posterior junction with basis. Carpus smooth, about 0.35 length of propodus in dorsal view, lacking prominent spines or teeth. Chela ( Fig. 9E, F ) smooth, with longitudinal crista on lower, external surface of palm, when measured along dorsal margin, about 2.5 times as long as high, about 0.85 of carapace width; fingers meeting at pointed tips, leaving wide hiatus when closed. Dactylus strongly arched; cutting edge with row of small, rounded teeth and 1 large subrectangular tooth at about mid-length; immovable finger nearly straight, cutting edge lined with low, rounded teeth, becoming sharper near tip.

Ambulatory legs ( Fig. 9A ) long, dorsoventrally compressed, smooth; P3> P4> P2> P5; length of P3 (merus to dactylus) about 1.6 times carapace width. Extensor margins of merus slightly concave (P2–4) or slightly convex (P5), lined proximally with setae, smooth or weakly granular, carinate; flexor margins smooth, rounded; merus of P3 about 5.3 times longer than wide. Carpi glabrous or each with few setae on extensor margin; carpus of P3 about 2.6 times longer than wide measured on extensor margin and widest surface in dorsal view; extensor margins carinate. Propodus glabrous or each with row of few short setae on flexor margin, longer than (P2–4) or subequal to (P5) carpus; extensor margins carinate. Dactylus glabrous, flattened, subequal to propodi measured along extensor margins, gradually tapering to acute apex; extensor margins straight (P2, P5) or slightly convex (P3, P4).

Thoracic sternum ( Fig. 9D ) wide; sternites 1 and 2 fused, anterior margin granular, demarcated from sternite 3 by row of granules; sternites 1–3 concave to accommodate setae of Mxp3; sternite 3 short; sterno-pleonal cavity almost reaching anterior margin of sternite 4; sternal condyle on sternite 5 near suture dividing sternites 4 and 5. Penis sternal, appearing in sterno-pleonal concavity on sternite 8.

Pleon ( Figs. 9D , 10D ) moderately wide; pleonite 1 short; pleonite 2 very short; pleonite 3 wider than pleonite 2 but narrower than pleonite 1; pleonites 4–6 fused, without indication of sutures; lateral margin of pleonite 6 broadest at half distance to telson, with socket for sternal condyle on inner surface. Telson ( Figs. 9D , 10D ) subtriangular, wider than long, distal margin rounded.

G1 ( Fig. 10A, B ) stout, subtriangular in cross-section, relatively straight, with tip curving against sterno-pleonal surface; base of chitinous distal beak emanating near pronounced dorsal rounded lobe; tip concave, partially obscured by short, stiff, simple setae. G2 short, stout, with truncated tip.

Females. Larger than in males. Carapace more ovate; anterolateral margin more convex; suborbital flange lacking. Chelae smaller, weaker than in males. Thoracic sternum with vulvae on anterior half of sternite 6, mesial process on anterior part of sternite 6. Lateral margins of all pleonites convex. Telson sub-rhomboidal; anterior margin convex.

Colour pattern. Somewhat variable. Carapace dorsal surface pale yellowish with dark-brown, greyish and/or whitish mottling and blackish or brownish spots of various sizes; cardiac area typically with larger central spot. Sternum pale yellow or whitish. Ocular peduncles with dark spots; cornea silvery with some spots. Chelipeds and ambulatory legs pale or greyish with small to large, dark brown spots and blotches; distal portion of carpi of ambulatory legs whitish; ventral surfaces of all ambulatory legs without or with feebly marked blotches ( Figs. 11 , 12 ).

Etymology. The new species is named after the late Dr. Ng Ngan Kee (National University of Singapore), for her important contributions to brachyuran systematics, especially in the family Varunidae , and for having always been a great friend and colleague.

Distribution. Northwestern Indian Ocean: presently known only from three localities in Oman, more precisely Sur, Al-Sawadi (west of Muscat), Masirah Island and Mirbat (east of Salalah, Dhofar).

Ecology. Nearshore sandflats, at depths of 0–1 m; in burrows of unknown hosts (presumably symbiotic, but may also excavate own burrows).

Remarks. Gopkittisak ngankeeae n. sp. possesses two diagnostic gaeticine characters, which are the presence of long setae on the Mxp3 palp and the fused male pleonites 3–5 ( Davie & Ng 2007). Gopkittisak ngankeeae n. sp. does not possess a longitudinal sternal sulcus to accommodate the Mxp3 filtering setae, but instead has an anterior sternal depression for this purpose (visible in Fig. 9D ); this character is also present in G. gallardoi and G. angustum ( Naruse & Clark 2009; Komai 2011). All three species of Gopkittisak have a laterally ovate carapace, with a posterior, transverse ridge, and share three important features on Mxp3: (1) presence of deep, longitudinal depressions on the ischium and merus (not illustrated by Serène & Soh 1976: fig. 28A); (2) oblique articulation between the ischium and merus; and 3) carpus proximally articulating along lateral half of the distal margin of the merus ( Figs. 9A, C , 10C ; Serène & Soh 1976: fig. 28B, pl. VIII, fig. A; Ghani & Tirmizi 1991: fig. 1C; Naruse & Clark 2009: figs. 1a, c, 3; Komai 2011: figs. 1, 2A, E, 5A). Importantly, the first two of the above-listed Mxp3 features are also present in Brankocleistostoma fossulum ( Fig. 6C ; Ng 2012: fig. 3D, E).

Gopkittisak ngankeeae n. sp. can be separated from its two congeners by the outline of the carapace, in which the convex anterolateral margin meets the posterolateral margin at a wide angle ( Fig. 9A ). In contrast, the lateral margins of the carapace are subparallel and less divergent posteriorly in G. gallardoi and G. angustum ( Serène & Soh 1976: fig. 28B, pl. VII, fig. A; Ghani & Tirmizi 1991: fig. 1A; Naruse & Clark 2009: figs. 1A, 3; Komai 2011: figs. 1, 2A). Male specimens of G. ngankeeae n. sp. are also distinguished by the presence of a flange lateral to the orbits, followed by several lobes, on the suborbital crista (vs. without such flange in G. gallardoi and G. angustum ) ( Fig. 9B, C ; Naruse & Clark 2009: fig. 1b; Komai, 2011: fig. 2D). Additionally, males of G. ngankeeae n. sp. have a keeled lobe located proximally on the anterior margin of the glabrous cheliped merus (vs. absent in G. gallardoi and G. angustum ; Fig. 9A, B ; proximal part of merus not illustrated in Naruse & Clark 2009 and Komai 2011, but this was confirmed by our examination of comparative material of the two species). The flange on the suborbital crista and a glabrous cheliped merus with a keeled lobe on the anterior margin may be involved in stridulation. In addition, the P3 and P4 propodi are glabrous or have a row of relatively few, short setae in G. ngankeeae n. sp. (vs. setose in G. gallardoi and G. angustum ; Fig. 9A ; Komai 2011: figs. 3E–G, 5B, C). This character, however, should be used with caution, as setation may be lost due to abrasion or vary with age, and the degree of setation in G. ngankeeae n. sp. sometimes approaches that of G. angustum .

Whereas G. ngankeeae n. sp. is readily distinguishable from its two congeners by the aforementioned characters, G. angustum and G. gallardoi are remarkably similar and differentiated based on characters that can vary among conspecifics, for example, cw to cl ratio due to age and setation due to abrasion. Colour patterns generally appear to be variable within each species of Gopkittisak ( Figs. 11 , 12 ) and therefore have rather limited value as an interspecific diagnostic character (but see above). The type material of G. gallardoi , deposited in the Phuket Marine Biological Center, Thailand, was unavailable for this study, although topotypic material collected from Phuket in 2018 (ZRC 2008.1053) was examined and compared with the material of G. angustum from Japan and the Philippines (see above). Examination of more material of these two species, as well as molecular analyses, will eventually clarify the geographical distributions and species limits of G. gallardoi and G. angustum and their relationship with G. ngankeeae n. sp.

Figures

FIGURE 6. Brankocleistostoma fossulum (Barnard, 1955), male (6.7/4.1), Farasan Islands, Saudi Arabia, FLMNH UF 36973: A, left G1, dorsal; B, same, ventral; C, third maxilliped, ventral; D, pleon and telson, ventral. Scales: 1 mm.

FIGURE 9. Gopkittisak ngankeeae n. sp., holotype, male (8.0/4.4), Sur, Oman, FLMNH UF 65444: A, habitus, dorsal; B, anterior surface of carapace and buccal frame, anterior (frontal); C, right Mxp3, anterior; D, sternum, pleon and telson, ventral; E, right chela, outer; E, left chela, outer. Photographs by R. Lasley.

FIGURE 10. Gopkittisak ngankeeae n. sp., holotype, male (8.0/4.4), Sur, Oman, FLMNH UF 65444: A, left G1, dorsal; B, same, ventral; C, Mxp3, ventral; D, pleon and telson, ventral. Scales: 1 mm.

FIGURE 11. Gopkittisak ngankeeae n. sp., paratype, male (7.2/4.1), Sur, Oman, FLMNH UF 65445, crab alive in different views: A, dorsal; B, ventral; C, anterior (frontal). Photographs by A. Anker.

FIGURE 12. Gopkittisak ngankeeae n. sp., crabs alive in dorsal view: A, paratype, male (7.9/4.2), Mirbat, Oman, FLMNH UF 63579; B, paratype, female (10.4/5.5), same locality, FLMNH UF 63805; C, female (cw/cl indet.), Masirah Island, Oman, FLMNH UF 69024. Photographs by A. Anker.