Austrothelphusa gilbertensis, Naser & Davie & Waltham, 2018

Naser, Murtada D., Davie, Peter J. F. & Waltham, Nathan J., 2018, Redescription of Austrothelphusa wasselli (Bishop, 1963) (Crustacea: Brachyura: Gecarcinucidae), and designation of a new species from the Gilbert River, north Queensland, Australia, Zootaxa 4369 (1), pp. 109-127 : 119-120

Austrothelphusa gilbertensis sp. nov.

( Figs 6D–F , 7B, D, G, H , 8–10 )

Material Examined. HOLOTYPE: QM-W28346, male (22.3 × 17.6 mm), Venture Creek , E of Croydon, Gilbert Catchment, Queensland, J. & S. Hasenpusch, 0 1.05.2006 . Paratypes: QM-W28040, 3 males (23.0 × 18.1, 22.9 × 18.1, 19.9 × 15.6 mm), 8 females (24.3 × 19.1, 24.3 × 19.1, 23.5 × 18.5, 22.6 × 17.9, 22.0 × 17.2, 19.8 × 15.6, 21.4 × 16.8, 18.4 × 14.5 mm), same data as holotype. QM-W28339, male (20.5 × 16.1 mm), small creek off Gilbert River, coll. Nathan Waltham, 9.05.2014. QM-W28305, female (16.0 × 12.6 mm), Pleasant Creek, off Gilbert River , coll. S. Hedge & J. Sariman, 0 3.04.2007.

Description. Small species (maximum CW of present material, female 24.3 mm). Carapace of mature specimens broadly oval ( Fig. 8A ), c. 1.27 times broader than long (range 1.26–1.28, n = 14). Front projecting beyond level of exorbital angles, prominently bilobed, medial concavity relatively deep; inner part of orbital cup poorly defined, merging broadly with lateral slope of frontal lobe ( Fig. 7B ). Frontal and orbital margins with raised rounded rims. Postfrontal (epigastric) lobes moderately well developed, bearing distinct striated ridges; separated by deep narrow groove. Postorbital region moderately depressed, short slightly convex crest laterally adjacent to, but not quite reaching, epibranchial tooth. Anterolateral margins smoothly cristate, evenly convex, distinct but small epibranchial tooth (relatively more prominent than in A. wasselli ). Branchial regions moderately but not markedly swollen, bearing punctations; anteriorly lacking striations but with striated ridges posterolaterally. Cervical groove shallow, relatively well defined, deeper than in A. wasselli ); gastro-cardiac (H-shaped) grooves relatively well defined. Posterolateral borders straight, convergent posteriorly.

Male pleon ( Fig. 6F , 8B , 10C ) broadly triangular; telson tapering, apically rounded, length subequal to breadth at base. Somite 6 slightly tapering (proximal width 1.26 times distal width), c. 1.38 times wider at base than long; with a pair of slightly raised transverse rounded crests distomedially. Somite 5 more strongly tapering (proximal width 1.54 times distal width), c. 2.75 times wider at base than long. Somite 4 also strongly tapering (proximal width 1.57 times distal width), c. 4.3 times wider at base than long. Somites 2 and 3 broad, with lateral margins evenly rounded, narrow.

Walking legs moderately long, total length of P5 (basis to tip of dactyl) c. 1.1 times maximum carapace width. P5 ( Fig. 7D ): merus with anterior and posterior borders diverging distally, relatively straight, 3.11 times longer than wide; propodus short, anterior border only weakly convex, 2.07 times longer than wide; dactylus short, slightly longer than propodus (1.12 times).

G1 ( Fig. 7G, H ) short, broad basally but tapering and slender over distal half, markedly curved inward apically. Outer lateral margin (in sternal view) broadly concave through medial third, before curving inwards towards apex. Terminal opening small, elongate V-shaped, apical flanges smoothly tapering. Some sparse long simple setae along inner margin towards tip.

Colour. Dorsal surfaces of fresh and recently preserved material are grey to yellowish-green; a scattering of well separated, small, but obvious and discrete red dots across the dorsal surfaces of the carapace, walking legs and claws. Ventral surfaces generally pale yellow. Frontal face of chelae pale yellow with an oblique broad band of orange behind the gape; tips of fingers orange ( Fig. 10 ).

Distribution and ecology. Only known from a restricted area in the central region of the Gilbert River Catchment ( Fig. 1 ), but further collecting will presumably find it to be more widespread within the catchment. Found in freshwater pools, and at the edge of small creeks, on clay and firm mud substrates; often under leaves.

Etymology. The species is named for its Gilbert River type locality.

Remarks. As already discussed the COI barcoding region for Austrothelphusa gilbertensis sp. nov. shows it to be genetically distinct from A. wasselli by 5.4–6.4% (also see further comment in the Discussion). Careful examination also shows a number of significant morphological differences that can be used to easily separate the two species:

Austrothelphusa gilbertensis sp. nov. differs from A. wasselli by: 1) having relatively more prominent epibranchial teeth; 2) the front has a relatively deep medial concavity ( Fig. 7B ), versus much shallower in A. wasselli ( Fig. 7A ); 3) the inner part of the orbital cup is poorly defined, broadly merging with the lateral slope of the frontal lobe ( Fig. 7B ), whereas in A. wasselli the inner part of the orbital cup is moderately well-defined, merging quite steeply with the lateral slope of the frontal lobe ( Fig. 7A ); 4) the postfrontal (epigastric) lobes are moderately well developed, bearing distinct striated ridges, versus not well developed, and lacking striated crests in A. wasselli ; 5) the cervical groove is relatively well defined, and deeper than in A. wasselli ; 6) the gastro-cardiac (H-shaped) grooves are relatively well defined, versus shallower and less defined in A. wasselli ; 7) somite 6 of the male pleon is c. 1.38 times wider at the base than long, versus c. 1.64 times in A. wasselli ; and bears a pair of slightly raised transverse rounded crests distomedially ( Fig. 9C ) that are lacking in A. wasselli ; 8) somite 5 of the male pleon is c. 2.75 times wider at base than long, versus c. 2.97 times in A. wasselli ; 9) the merus of P5 has the anterior and posterior borders diverging distally, relatively straight, and 3.11 times longer than wide ( Fig. 6D ), versus anterior and posterior borders subparallel, slightly convex, and only 2.77 times longer than wide in A. wasselli ( Fig. 6C ); 10) the G1 is markedly curved inward apically, with the outer lateral margin (in sternal view) broadly concave through the medial third ( Fig. 7G ), versus moderately curved inward apically, and outer lateral margin relatively straight over the basal two-thirds in A. wasselli ( Fig. 7E ); and finally, 11) the live colour patterns differ— A. gilbertensis has obvious small well-spaced dark spots across the anterolateral and medial parts of the carapace ( Fig. 10 ), whereas A. wasselli has more of a speckling of fine small red dots, across the anterolateral half of the carapace.

Figures

FIGURE 1. Map of Cape York, Queensland showing catchments and localities that were sampled for the present study. In the GilbertCatchment,black pentagon = Venture Creek, dark green hexagon = small branchof GilbertRiver,and purple diamond= Pleasant Creek; in the Normanby Catchment, light green spot= Healy Creek; in the Jeannie catchment, blue oval = Howick River; in the Stewart Catchment, red rectangle = Stewart River; and in the Archer Catchment, yellow triangle = Oscar Creek (see Table 1 for precise localities). The crab shown is the holotype male of Austrothelphusa gilbertensis sp. nov. (refer to Fig. 8).

FIGURE 6. A–C, Austrothelphusa wasselli, male (18.8 × 14.9 mm), Oscar Creek, 2.1 km SSE of Coen, Archer Catchment, Queensland (QM-W29187). D–F, A. gilbertensis sp.nov., holotype male (11.2 × 9.2 mm), Port Stewart District, Cape York (AM-P.14524).A, D, ventrofrontal view of cephalothorax (orbit, frontal triangle, epistome and pterygostome); B, E, left major chela; C, F, pleon. Scale line 5 mm.

FIGURE 7. A, C, E, F, Austrothelphusa wasselli, male (25.8 × 20.5 mm), from Stewart River, Queensland (QM-W20049). B, D, G, H, A. gilbertensis sp. nov., holotype male (22.3 × 17.6 mm), Venture Creek, E of Croydon, Gilbert Catchment, Queensland (QM-W28040). A, B, outline of frontal margin and orbits; C, D, fifth pereiopod; E–H, left first gonopod (sternal view) with magnification of apical part.

FIGURE 9. Austrothelphusa gilbertensis sp. nov., holotype male (22.3 × 17.6 mm). A, ventrofrontal view, showing maxillipeds; B, outer view, showing chelipeds.

FIGURE 10. Live colouration of Austrothelphusa gilbertensis sp. nov., male (20.5 × 16.1 mm), small creek off Gilbert River (QM-W28339). A, dorsal view; B, frontal view; C, ventral view.

FIGURE8. Austrothelphusa gilbertensis sp. nov., holotype male (22.3 × 17.6 mm).A, dorsal view; B, ventral view of sternum and pleon.