Typhlocarcinops arcuatus (Miers, 1884)

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 : 92-94

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-FFF9-FC51-FF35-D3C0FD48FD4D
treatment provided by	Plazi
scientific name	Typhlocarcinops arcuatus (Miers, 1884)
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Typhlocarcinops arcuatus (Miers, 1884) View in CoL

( Figs. 78–80 View FIGURE 78 View FIGURE 79 View FIGURE 80 )

Ceratoplax arcuata Miers, 1884: 243 View in CoL , pl. 25B.

Typhlocarcinops decrescens View in CoL — Tesch 1918: 213, pl. 13 fig. 4 (not Typhlocarcinops decrescens Rathbun, 1914 View in CoL ). Typhlocarcinops arcuata View in CoL — Ng 1987: 78, 88.

Typhlocarcinops arcuatus View in CoL — Ng et al. 2008: 144.

Material examined. Holotype: male (6.5 × 6.0 mm) ( NNM 1882.7 View Materials ), Port Darwin , Australia, coll. H.M.S. Alert, 1882.

Diagnosis. Carapace ( Figs. 78A, B View FIGURE 78 , 80A View FIGURE 80 ) slightly broader than long, width to length ratio 1.1, surface covered with short pubescence; anterolateral margin gently arcuate, with 3 low notches forming 4 broad lobes. Front ( Fig. 78A, B View FIGURE 78 ) slightly deflexed with shallow but distinct median cleft; margins distinctly convex. Orbit ( Figs. 78B, C View FIGURE 78 , 80A View FIGURE 80 ) shallow, ocular peduncles filling orbit, immovable, cornea small. Third maxilliped ( Fig. 80B View FIGURE 80 ) broad, merus transverse, anteroexternal angle prominent, protruding, auriculiform. Cheliped ( Fig. 79 View FIGURE 79 A–D) moderately large, sur- face covered with small granules to smooth, palm slightly longer than broad, outer surface of major chela mostly smooth, that of minor chela covered with small granules; fingers gaping when closed; cutting edges of fingers lined with sharp teeth and denticles; inner angle of carpus with distinct tooth. P2‒P5 ( Figs. 78A View FIGURE 78 , 79 View FIGURE 79 E–G) slender; P2–P4 dactylus slender, gently curved; P5 dactylus straight. Male pleon ( Fig. 80D View FIGURE 80 ) narrow, telson short, 1.4 times as long as somite 6, triangular with rounded distal margin. G1 ( Fig. 80E, F View FIGURE 80 ) slender, sinuous, upper and lower halves subequal, distal part slender, curved, tapering to pointed tip.

Remarks. Miers (1884) described Ceratoplax arcuata from one small 6.6 × 6.0 mm male collected from northern Australia and Miers (1886: 235) subsequently recorded it from Papua New Guinea. Ng (1987) noted that Miers described the anteroexternal angle of the merus of the third maxilliped as “prominent” (Miers 1884: 244) and the figure of the male pleon ( Fig. 78D View FIGURE 78 ) shows a narrow and extremely wide somite 1; and as such, commented that the species should be transferred to Typhlocarcinops instead. The examination of the type specimen confirms this generic assignment.

With regards to the more subovate carapace and strongly auriculiform anteroexternal angle of the third maxilliped, T. arcuatus is probably most closely related to T. angustipes . The two species, however, differ markedly in other characters. In T. arcuatus , the anterolateral margin has four low lobes ( Fig. 80A View FIGURE 80 ) (versus only one low lobe in T. angustipes ; Fig. 77A View FIGURE 77 ); the ambulatory legs are relatively longer and more slender ( Figs. 78A View FIGURE 78 , 79 View FIGURE 79 E–G) (versus shorter and stouter in T. angustipes ; Fig. 76A, B View FIGURE 76 ); the male pleon is proportionately transversely more narrow ( Fig. 80D View FIGURE 80 ) (versus proportionately broader in T. angustipes ; Fig. 77C View FIGURE 77 ); and the G1 is distinctly more sinuous ( Fig. 80E, F View FIGURE 80 ) (versus relatively stouter in T. angustipes ; Fig. 77D, E View FIGURE 77 ).

As discussed above, Tesch’s (1918: 213, pl. 13 fig. 4) records of “ T. decrescens ” from Talaut Island in the Moluccas and Roma Island north of Timor should probably be referred to T. arcuata instead.

With regards to the female specimen of Miers (1886) (1 female (11.5 × 9.3 mm) (NHM), station 188, south of New Guinea, 9º59’0”S 139°42’0”E, 28 fathoms, coll. H.M.S. Challenger) ( Fig. 81 View FIGURE 81 ), he noted that “This example is of much larger size than the small male described in the Report cited; the whole animal is more pubescent and the carapace proportionately broader; the subdistal tooth or prominence on the upper margin of the merus of the chelipedes, which is obscurely indicated in the original type, is more distinctly developed.” (Miers 1886: 235). Although a female, examination of this specimen shows that it is not a species of Typhlocarcinops . The female thoracic sternum is relatively narrow transversely and pleonal somite 1, while almost reaching the coxae of the last ambulatory legs, is not extremely wide ( Fig. 81 View FIGURE 81 B–D). This is more akin to the condition observed in Heteropilumnus species (cf. Fig. 4C, D View FIGURE 4 ). The general appearance of the carapace, third maxillipeds and chelipeds ( Figs. 81 View FIGURE 81 , 82A View FIGURE 82 , E–H) are also more similar to species of Heteropilumnus (cf. Ng et al. 2018) ( Fig. 82 View FIGURE 82 ).