Typhlocarcinops diminutus, Ng & Rahayu, 2020

Ng, Peter K. L. & Rahayu, Dwi Listyo, 2020, A synopsis of Typhlocarcinops Rathbun, 1909 (Crustacea: Decapoda: Brachyura: Pilumnidae), with descriptions of nine new species from the Indo-West Pacific, Zootaxa 4788 (1), pp. 1-100 : 80-83

publication ID	https://doi.org/ 10.11646/zootaxa.4788.1.1
publication LSID	lsid:zoobank.org:pub:7A461DBA-00B7-48DB-9320-4775DA8F21B2
persistent identifier	https://treatment.plazi.org/id/03C05222-FFED-FC5E-FF35-D6A5FA8EFDD1
treatment provided by	Plazi
scientific name	Typhlocarcinops diminutus
status	sp. nov.

Treatment

Typhlocarcinops diminutus View in CoL n. sp.

( Figs. 67–69 View FIGURE 67 View FIGURE 68 View FIGURE 69 )

Material examined. Holotype: male (3.5 × 2.5 mm) ( ZRC 2018.0295 View Materials ), dredge, station PS252, Pulau Semakau , Singapore, coll. 1990s . Paratypes: 3 males (4.2 × 2.9 mm, 2.9 × 2.4 mm, 3.3 × 2.7 mm); 2 females 3.8 × 2.9 mm, 2.9 × 2.2 mm); 1 ovigerous female (3.6 × 2.7 mm) ( ZRC 1992 View Materials 5955–5999), Pulau Semakau , Singapore, coll. 27 January 1992 .

Diagnosis. Carapace ( Figs. 67A, B View FIGURE 67 , 68 View FIGURE 68 A–D) 1.2−1.4 times broader than long, slightly narrowing on posterolat- eral margin, surface with tufts of short plumose setae, regions demarcated, H-shaped gastro-cardiac grooves shallow, indistinct, anterolateral margin arcuate, lined with small granules, separated by 3 broad, sharp teeth; posterolateral margin subparallel posterolateral surface with scattered tubercles. Front bilobed ( Figs. 67B View FIGURE 67 , 68 View FIGURE 68 B–D), with shallow median cleft, margin of each lobe convex. Orbit ( Fig. 67C View FIGURE 67 ) short, bulbous ocular peduncles filling orbit, immovable, cornea small, pigmented. Epistome ( Fig. 67C View FIGURE 67 ) relatively broad, triangular median lobe with slight median suture. Antennal peduncles long. Third maxilliped ( Figs. 67C View FIGURE 67 , 69A View FIGURE 69 ) with outer surface of merus covered with small granules on distal margin, outer margin straight, inner margin sinuous, anteroexternal angle gently produced; ischium as broad, but much longer than merus, inner margin slightly shorter than outer margin; exopod relatively slender. Chelipeds unequal in males, subequal in females ( Figs. 67 View FIGURE 67 E–G, 68A), fingers of major chela smooth, outer surface of dactylus and fixed finger with longitudinal ridge, long fine setae on upper and lower margins of dactylus and fixed finger, cutting edges with prominent broad teeth; palm, carpus and merus smooth, tufts of sparse setae on its surfaces; inner angle of carpus with sharp low tooth ( Fig. 67E View FIGURE 67 ). P2−P5 proportionally long ( Figs. 67A, H View FIGURE 67 , 68A View FIGURE 68 ); dorsal margin of the merus of first to third ambulatory legs smooth, unarmed; lateral surface, dorsal and ventral margins fringe with long setae; dactylus straight, relatively long; merus of P5 not reaching front when folded. Fused thoracic sternites 1, 2 broadly triangular ( Fig. 67C, D View FIGURE 67 ), proportionally narrow; thoracic sternites 3, 4 fused, suture discernible. Male pleon ( Fig. 69B View FIGURE 69 ) relatively broad; telson relatively short, 1.5 times as long as somite 6, with rounded distal margin. G1 ( Fig. 69C, D View FIGURE 69 ) slender, upper and lower halves subequal, moderately curved, distal part strongly curved, relatively long and slender, tapering to relatively sharp tip, with setae subdistally. Female pleon ( Fig. 68E View FIGURE 68 ) broad, somite 1 reaching coxae of fourth ambulatory legs; telson with rounded distal margin; tapering to pointed edge; vulva ( Fig. 68F View FIGURE 68 ) relatively broad, rounded.

Etymology. From the Latin “diminutus” for small sized, alluding to the small adult size of the species.

Remarks. The general appearance of the species superficially resembles members of Heteropilumnus De Man, 1895 , and its allies ( Ser Rathbun, 1931 ; Zehntneriana Ng & Takeda, 2010 ), except that it lacks the long setae that lines the margins of the carapace, chelipeds and ambulatory legs and/or the dense velvet-like tomentum that covers the carapace (cf. Ng 1989; Ng & Davie 1991; Ng & Lin 2015; Ng & Tan 1988; Ng et al. 2018; Lee et al. 2015).

Like any other species assigned to Typhlocarcinops , the anterolateral margin of carapace is varied in relation with size and sex. The larger male (carapace width 4.2 × 2.9 mm) and the females have less pronounced lobes on the anterolateral margin than the small one. The dactylus and fixed finger of the chelipeds of the larger male are without longitudinal ridge.

The species most resembles T. canaliculatus , but differs in the shape of the carapace in which the posterolateral margin is slightly narrowing, the G1 with the upper and lower halves are subequal, moderately curved in T. diminutus n. sp. ( Figs. 67A, B View FIGURE 67 , 68 View FIGURE 68 B‒D, 69C, D), versus the posterolateral margin of the carapace is parallel and the upper half of G1 is much longer than the lower half, strongly curved in T. canaliculatus ( Figs. 5B, C View FIGURE 5 , 7A, D View FIGURE 7 , 8B View FIGURE 8 , 9B, C View FIGURE 9 , 10A View FIGURE 10 , 11B View FIGURE 11 , 12B View FIGURE 12 , 13 View FIGURE 13 D‒G, I‒L, 14B‒E, H‒K, 15E‒G, 40A–C).