Typhlocarcinops decrescens Rathbun, 1914

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 : 21-26

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-FFB6-FC15-FF35-D0B0FD4CFDA9
treatment provided by	Plazi
scientific name	Typhlocarcinops decrescens Rathbun, 1914
status

Treatment

Typhlocarcinops decrescens Rathbun, 1914 View in CoL

( Figs. 16–24 View FIGURE 16 View FIGURE 17 View FIGURE 18 View FIGURE 19 View FIGURE 20 View FIGURE 21 View FIGURE 22 View FIGURE 23 View FIGURE 24 , 40 View FIGURE 40 D–F)

Typhlocarcinops decrescens Rathbun, 1914: 151 View in CoL ; Sakai 1965: 171, text-figs. 22a-d, pl. 84 fig. 5; 1976: 546, text figs. 293a, b, pl. 195 fig. 2; Ng et al. 2008: 144.

Typhlocarcinops genkaiae Takeda & Miyake, 1972: 262 View in CoL , fig. 5; Ng 1987: 78; Ng et al. 2008: 144.

Typhlocarcinops canaliculata View in CoL — Dai et al. 1986: 383, text fig. 202(2) (incorrectly labelled as Typhlocarcinops denticarpus sp. nov.), pl. 55(6); Dai & Yang 1991: 413, text fig. 202(2) (incorrectly labelled as Typhlocarcinops denticarpus sp. nov.), pl. 55(6). (not Typhlocarcinops canaliculata Rathbun, 1909 View in CoL )

Material examined. Holotype: male (9.7 × 7.6 mm) ( USNM 46407 View Materials ), station 5161, Tawi-tawi Island , Sulu Archi-

pelago, Philippines, 22–29 m, coll. RV Albatross, 22 February 1908. Paratypes: 3 males (9.1 × 7.5 mm, 7.1 × 5.8 mm, 6.8 × 5.5 mm), 2 females (9.8 × 7.5 mm, 7.6 × 5.5 mm) ( USNM 122579 View Materials ), same data as holotype. Others : 1 male (6.1 × 4.5 mm) (AS 2137), Xiamen, Fujian, China ; 1 female (8.0 × 5.6 mm) (AS 13251), Shandung, China, coll. 2 May 1935 ; 1 male (15.2 × 11.9 mm) ( ZRC 2018.0699 View Materials ), station W1, Hong Kong, coll. University of Hong Kong trawls, 16 July 2015 ; 1 female (15.3 × 11.6 mm) ( ZRC 2018.0695 View Materials ), Lantau, Hong Kong, coll. University of Hong Kong trawls, 28 July 2007 ; 1 male (6.8 × 5.3 mm) ( ZRC 2018.0269 View Materials ), station A4B, Digul, Arafura Sea, 5°06’15.31’’S 136°37’58.69’’E, Papua, Indonesia, 8 November 2000 GoogleMaps .

Diagnosis. Carapace ( Figs. 16B View FIGURE 16 , 17A, B View FIGURE 17 , 18A View FIGURE 18 , 19B View FIGURE 19 , 20A View FIGURE 20 , 21A View FIGURE 21 , 22B View FIGURE 22 ) about 1.2−1.3 times broader than long, surface smooth, regions indistinct, H-shaped gastro-cardiac grooves very shallow, barely visible and not discernible, intestinal groove slightly deeper; anterolateral margin arcuate, lined with tiny granules, separated by 4 broad, low, lobes; posterolateral surface and margin with scarce, scattered tubercles. Front ( Figs. 16B, C View FIGURE 16 , 17A, B View FIGURE 17 , 18A View FIGURE 18 , 19B, D View FIGURE 19 , 20A, B View FIGURE 20 , 21A, B View FIGURE 21 , 22B, C View FIGURE 22 ) bilobed, with shallow median cleft, margin of each lobe slightly convex. Orbit ( Figs. 16C View FIGURE 16 , 19D View FIGURE 19 , 20B View FIGURE 20 , 21B View FIGURE 21 , 22C View FIGURE 22 ) short, bulbous ocular peduncles filling orbit, immovable, cornea very small, slightly pigmented. Epistome ( Figs. 16C View FIGURE 16 , 19D View FIGURE 19 , 20B View FIGURE 20 , 21B View FIGURE 21 , 22C View FIGURE 22 ) relatively broad, triangular median lobe with median suture. Antennal peduncles relatively long. Third maxilliped ( Figs. 18B View FIGURE 18 , 19C View FIGURE 19 , 21C View FIGURE 21 , 23A, F View FIGURE 23 ) with merus broad, squarish, outer and inner margins straight, ischium slightly broader, longer than merus, inner margin slightly shorter than outer margin, lower margin slightly oblique; exopod stout, relatively broad, tip reaching to just before distal edge of merus, inner margin with distinct tooth. Chelipeds unequal in males, subequal in females ( Figs. 16A, F, G View FIGURE 16 , 17A, B View FIGURE 17 , 18C View FIGURE 18 , 19A, E, F View FIGURE 19 , 20C, E, F View FIGURE 20 , 21 View FIGURE 21 D–F, 22F–H), outer surface of fingers of chela smooth, with longitudinal ridge and scattered tubercles proximally on dactylus and fixed finger, surface of palm smooth medially, upper, lower outer surface with dense, short, setae, denser setae on minor chela; cutting edges of fingers with prominent teeth; upper outer surface of carpus with small tubercles, smooth medially, short, broad tooth on inner angle ( Figs. 19F View FIGURE 19 , 20C View FIGURE 20 , 21D View FIGURE 21 , 22G, H View FIGURE 22 ); lower outer surface of merus with scattered tubercles, margins covered with short setae. P2−P5 ( Figs. 16A View FIGURE 16 , 17A, B View FIGURE 17 , 19A, G View FIGURE 19 , 22A View FIGURE 22 ) proportionally long, fringe by sparse long setae on dorsal and ventral margins; merus of P5 not reaching front when folded. Fused thoracic sternites 1, 2 broadly triangular ( Figs. 16D View FIGURE 16 , 17D View FIGURE 17 , 19H View FIGURE 19 , 21C View FIGURE 21 , 22D View FIGURE 22 ), proportionally broad; thoracic sternites 3, 4 partially fused, with only lateral suture discernible. Male pleon ( Figs. 16D, E View FIGURE 16 , 18D View FIGURE 18 , 19H, I View FIGURE 19 , 20D View FIGURE 20 , 21C View FIGURE 21 , 23G View FIGURE 23 , 24H View FIGURE 24 ) relatively broad, telson long, 1.7 times as long as somite 6, subtriangular with rounded distal margin. G1 ( Figs. 18E, F View FIGURE 18 , 23 View FIGURE 23 B–E, H–K, 24A–G, 40D–F) slender, curved, upper and lower halves, distal part elongate, strongly curved, with pointed tip. Female pleon broad, so1 reaching cx5, tapering to pointed edge ( Figs. 17C View FIGURE 17 , 22D View FIGURE 22 ); vulva large, ovate; telson subtriangular ( Figs. 17D View FIGURE 17 , 22E View FIGURE 22 ).

Remarks. Typhlocarcinops genkaiae Takeda & Miyake, 1972 , was described from a small 5.4 × 4.0 mm male collected near Tsushima Islands, Japan and is probably a junior synonym of T. decrescens . The G1 of this species ( Takeda & Miyake 1972: fig. 5I, J; present Fig. 18E, F View FIGURE 18 ) agrees well with T. decrescens ( Figs. 23 View FIGURE 23 B–E, H–K, 24A–G, 40D–F), as does the general shape of the male pleon, third maxilliped and chelae ( Takeda & Miyake 1972: fig. 5C, D, H; present Fig. 18 View FIGURE 18 A–C). The only unusual feature of the T. genkaiae type male is that the anterolateral margin of the carapace has two low but sharp teeth, including one at the junction of the antero- and posterolateral margins ( Takeda & Miyake 1972: fig. 5A; present Fig. 18A View FIGURE 18 ), a character not yet known from any specimen of T. decrescens examined. Furthermore, the type male of T. genkaiae is small and the anterolateral armature may just be due to variation.

Dai et al. (1986) and Dai & Yang (1991) recorded a male ( AS 2137) and a female ( AS 13251) specimen of “ Typhlocarcinops canaliculatus ” from southern China and noted that the anterolateral margins were entire. Both specimens were examined and this is confirmed. As discussed below (see Remarks for T. denticarpes ), the G1 structures figured of “ T. canaliculatus ” and T. denticarpes by Dai et al. (1986) and Dai & Yang (1991) were accidentally transposed. Their figure of the G1 of “ T. canaliculatus ” (incorrectly attributed to T. denticarpes ) is diagnostic as it shows a sinuous structure with the upper and lower halves subequal in length and the distal part not prominently elongate (cf. Dai et al. 1986: text fig. 202(1); Dai & Yang 1991: text fig. 202(1); present Fig. 24 View FIGURE 24 A–D). The G1 of the male specimen examined has the distal part of the G1 slightly shorter, with the tip not as elongate ( Fig. 24C, D View FIGURE 24 ) as figured by them ( Fig. 24A, B View FIGURE 24 ). This we can attribute to possible shrinkage of the distal part which does appear somewhat wrinkled. Regardless, the G1 of their “ T. canaliculatus ” otherwise matches that of T. decrescens . They also agree in the structures of their male pleons and chelipeds.

Tesch (1918: 213, pl. 13 fig. 4) records “ T. decrescens ” from a 5.1 × 3.75 mm male from Talaut Island in the Moluccas and a 6.25 × 5.3 mm female from Roma Island north of Timor; but Sakai (1976: 546) argues that his specimens belong to a different species as its carapace was too narrow. On the basis of his figure and especially its carapace shape, it resembles T. arcuata Miers, 1884 , described from a single male measuring 6.5 × 6.0 mm from Darwin in northwestern Australia. These locations are not far apart and the specimens of Tesch (1918) and Miers (1884) are probably conspecific (see discussion for that species).

Type locality. Sulu Archipelago , Philippines .

Distribution. Philippines, Indonesia (Talaut and Roma Island, north of Timor and Papua); Hong Kong; southern China; and Japan. On soft sediments 22– 29 m.