Dicranodromia robusta, Ng & Yang, 2021

Ng, Peter K. L. & Yang, Chien-Hui, 2021, On two new species of deep-sea carrier crabs (Crustacea, Brachyura, Homolodromiidae, Dicranodromia) from Taiwan and the Philippines, with notes on other Indo-West Pacific species, ZooKeys 1072, pp. 129-165 : 129

publication ID	https://dx.doi.org/10.3897/zookeys.1072.72978
persistent identifier	https://treatment.plazi.org/id/E5583473-0569-5F91-A871-19A9F9822336
treatment provided by	ZooKeys by Pensoft
scientific name	Dicranodromia robusta
status	sp. nov.

Treatment

Dicranodromia robusta sp. nov.

Figures 17 View Figure 17 , 18 View Figure 18 , 19 View Figure 19 , 20 View Figure 20 , 21C, G-J, N-P View Figure 21

Material examined.

Philippines: Holotype ♀ (19.6 × 26.4 mm), ca. 5°24'N, 125°22.5'E, Balut Island, Sarangani Islands, Davao Occidental Province , south of Mindanao Island , coll. tangle nets, local fishermen, 26 Nov. 2017 (ZRC 2018.0161) GoogleMaps ; Paratype ♂ (15.2 × 21.0 mm), same location as holotype, coll. tangle nets, local fishermen, 2017 (ZRC 2018.0095) GoogleMaps .

Diagnosis.

Carapace longitudinally subquadrate, widest across intestinal-mesobranchial regions; dorsal surface gently convex, lateral surfaces covered with low spinules, median part smooth, margins with scattered short stiff setae, not obscuring margins; short stiff setae present on pereiopods, thoracic sternum and pleon but not obscuring surface or margins. Branchiocardiac groove distinct, curving medially anteriorly. Each pseudorostral lobe triangular, inner margin straight, outer margin gently convex, directed anteriorly, inner margin entire; exorbital tooth dentiform, directed obliquely laterally, anterior margin with two or three spinules; supraorbital margin separated from external orbital tooth by shallow concave cleft, posterior part with five or six spinules; infraorbital margin with large dorsoventrally flattened lobe which is dentiform to linguiform, larger than exorbital tooth, distal part with spine, anterior margin with two spinules, prominently visible in dorsal view. Rostrum present as one sharp granule. Epistome covered with scattered granules on anterior half; posterior half gently upturned, with median fissure, surface not covered with spinules, posterior margin gently convex, median part entire, lateral part gently serrate. Basal antennal article subquadrate; surfaces covered by spinules and granules; anteroexternal tooth short. Eyes with long peduncle. Third maxilliped relatively narrow; merus subovate with low anterointernal lobe, shorter than ischium; ischium subtrapezoidal, distal half slightly wider than proximal part; palp (carpus, propodus, dactylus) long, reaching to median part of ischium when folded; exopod with proximal third widest. Chelipeds covered with stiff setae on most parts; merus and carpus with margins uneven or lined with granules; palm relatively short, subdorsal and subventral margins with low sharp granules, median part smooth; fingers thick, wide, occluding surface hollowed; pollex with deep U-shaped depression distally. P2 and P3 relatively short, P3 longer than P2; merus with low tooth on distal extensor margin, length to width ratio of P2 and P3 merus 4.2 and 3.9, respectively; margins unarmed; propodus almost straight, unarmed, length to width ratio of P2 and P3 propodus 5.2 and 6.4, respectively; dactylus curved, flexor margin lined with 8 or 9 spines, terminating in strongly gently curved claw, propodus about 2.4 × length of dactylus. P4 stouter, shorter than P5; length to width ratio of P4 and P5 merus 2.4 and 3.4, respectively; margins of merus unarmed; P4 and P5 propodus with submedian spinule on distal third of outer surface, length to width ratio of P4 and P5 propodus 2.3 and 3.6, respectively, distal margin fringed by sharp spines bracketing dactylus; dactylus claw-like, strongly incurved, extensor margin with median spine or absent, flexor margin with 2-4 spines. Thoracic sternite 7 with low transverse ridge from posterior inner part of female gonopore, lateral part high, forming triangular tubercle, curving posteriorly to join oblique ridge formed by posterior part of sternite 7, just before suture with sternite 8, groove between sternites 7 and 8 curve to join spermathecal aperture at base of triangular tubercle. Male and female pleons with 6 free somites and telson; male telson distinctly elongate, triangular with gently convex lateral margins; female telson triangular, with gently convex margins. G1 stout, endopod distally covered by dense long setae, subdistal part of outer margin with two lobes, the distal one being more prominent; G2 endopod gradually tapering to sharp tip.

Variation.

In the holotype female, the left P5 dactylus has a prominent spine on the extensor margin (Fig. 21I View Figure 21 ), but there is none on the right side (Fig. 21H View Figure 21 ). The P5 dactyli of the paratype male are armed a spinule on the extensor margin. Both specimens possess the spine on the outer surface of the P5 propodus (Fig. 21H, I View Figure 21 ).

Etymology.

The species is named after the Latin robusta for stout, alluding to the stocky appearance of the species.

Remarks.

The most diagnostic character of D. robusta sp. nov. is the large dorsoventrally flattened infraorbital tooth, which is dentiform to linguiform, clearly visible in dorsal view, and distinctly larger than the exorbital tooth (Figs 17B-D View Figure 17 , 20B View Figure 20 ). No other Indo-West Pacific species of Dicranodromia has such a large and wide infraorbital tooth. The long anteroexternal tooth on the basal antennal article allies D. robusta with D. martini (cf. Guinot 1995: fig. 20B), D. baffini (cf. Alcock 1899: pl. 2 fig. 1a; Alcock 1901: pl. 1 fig. 1a), D. danielae (cf. Ng and McLay 2005: fig. 3A, B) and D. chenae (cf. Ng and Naruse 2007: fig. 5b) but the structure of the infraorbital tooth easily distinguishes it from them.

The carapace shape of D. robusta is distinctly more quadrate (Figs 17A, B View Figure 17 , 20A, B View Figure 20 ) than the more pyriform D. martini described from the Philippines (cf. Figs 4A, C View Figure 4 , 6A, B View Figure 6 ; Guinot 1995: fig. 19b; Ng and Naruse 2007: fig. 1a-c); the posterior margin of the epistome is entire (Fig. 18C View Figure 18 ) (versus margin gently crenulate in subventral view in D. martini , cf. Guinot 1995: fig. 20B); P2 and P3 are prominently shorter with the dactylus especially short (e.g., P3 merus 3.9 × longer than broad, propodus 6.4 × longer than broad, Fig. 19A View Figure 19 ) (versus P3 merus 7.0 × longer than broad, propodus 7.2 × longer than broad in D. martini , cf. Figs 4A View Figure 4 , 5C View Figure 5 , 6A View Figure 6 ; Guinot 1995: figs 19a, e, 20C); P4 and P5 are much shorter (e.g., P4 merus just reaching branchiocardiac groove when folded dorsally, Figs 17A View Figure 17 , 19B View Figure 19 , 20A View Figure 20 ) (versus P4 merus long, reaching beyond branchiocardiac groove when folded dorsally in D. martini , cf. Figs 4A View Figure 4 , 5D View Figure 5 , 6A View Figure 6 ; Guinot 1995: fig. 19a); and the male telson is lingulate (Fig. 20C View Figure 20 ) (versus more elongate in D. martini , cf. Fig. 6D View Figure 6 ; Guinot 1995: fig. 19c).

Compared to D. baffini from the Indian Ocean, D. robusta has a more quadrate carapace (Figs 17A, B View Figure 17 , 20A, B View Figure 20 ) (versus more pyriform in D. baffini , cf. Alcock 1899: pl. 2 fig. 1a; Guinot 1995: fig. 13; Padate et al. 2020: fig. 2a); and the P2 and P3 dactylus is distinctly shorter (Figs 19A View Figure 19 , 21G View Figure 21 ) (versus longer in D. baffini , cf. Alcock 1899: pl. 2 fig. 1a; Guinot 1995: fig. 13). With regards to the relatively shorter P2 and P3 dactyli, D. robusta resembles D. chenae , described from a single large ovigerous female from the central Philippines. Dicranodromia robusta , however, can easily be distinguished in having the outer margin of the pseudorostral lobe is almost straight and the structure is directed anteriorly (Figs 17B-D View Figure 17 , 20B View Figure 20 ) (versus outer margin of the pseudorostral lobe is distinctly convex with the structure gradually curved inwards towards the median in D. chenae , cf. Ng and Naruse 2007: fig. 5A); the ischium of the third maxilliped is short and rectangular (Fig. 18B View Figure 18 ) (versus distinctly longer and more slender in D. chenae , cf. Ng and Naruse 2007: fig. 5b); the female telson is relatively more elongate (Fig. 18A View Figure 18 ) (versus proportionately wider and shorter in D. chenae , cf. Ng and Naruse 2007: fig. 2b); and the spermatheca is on the prominently raised part around the suture between sternites 7 and 8 and ends at the centre of the triangular tubercle on sternite 6 (Fig. 19F View Figure 19 ) (versus spermatheca is not prominently raised and ends at the base of the triangular tubercle in D. chenae , cf. Ng and Naruse 2007: fig. 8).

Dicranodromia robusta can be separated from D. danielae in having the exorbital tooth distinctly triangular to linguiform (Figs 17B-D View Figure 17 , 21C View Figure 21 ) (versus subtrapezoidal in D. danielae , cf. Fig. 12A, B View Figure 12 ; Ng and McLay 2005: figs 1B, 4A); the posterior margin of the epistome is entire (Fig. 18C View Figure 18 ) (versus clearly serrate in D. danielae , cf. Fig. 12C View Figure 12 ; Ng and McLay 2005: fig. 4C); the median part of the outer surface of the chela is granular (Fig. 18E, F View Figure 18 ) (versus smooth in D. danielae , cf. Fig. 12D View Figure 12 ; Ng and McLay 2005: fig. 3A, B); and P2-P5 are all proportionately longer with the flexor margins of the meri not spinate (Figs 17A View Figure 17 , 19A View Figure 19 , 20A View Figure 20 ) (versus relatively shorter in D. danielae with the meri of P2 and P3 distinctly spinate, cf. Fig. 12E, F View Figure 12 ; Ng and McLay 2005: fig. 1A).