Parasesarma sigillatum ( Tweedie, 1950 )

Ng, Peter K. L., Davie, Peter J. F. & Li, Jheng-Jhang, 2016, On the identities of Parasesarma carolinense (Rathbun, 1907) and Parasesarma sigillatum (Tweedie, 1950), with description of a new species from Taiwan (Crustacea: Brachyura: Sesarmidae), Raffles Bulletin of Zoology 64, pp. 257-268 : 261-264

Parasesarma sigillatum ( Tweedie, 1950)

( Figs. 1A–D ; 3 ; 5D–G ; 6G–M ; 7A )

Sesarma sigillata Tweedie, 1950: 131 , fig. 3a–e.

Sesarma (Parasesarma) sigillatum – Serène, 1968: 108.

Parasesarma carolinense – Ng et al., 2008: 222 (list, part) (not Sesarma (Parasesarma) carolinensis Rathbun, 1907 ).

Material examined. Lectotype (here designated): male (10.7 × 7.6 mm) ( NHM 1950.4.17.4), Cocos-Keeling Islands , coll. C.A. Gibson-Hill, 1941 . Paralectotype: 1 female (10.4 × 7.5 mm) ( NHM 1950.4.17.5), same data as lectotype. Others : 24 males (largest 11.1 × 7.8 mm), 20 females (largest 11.0 × 7.8 mm) (1 ovigerous) ( ZRC 1965.8.2.260–269), Cocos- Keeling Islands , coll. C.A. Gibson-Hill , 1941; 1 female (9.9 × 7.0 mm) ( ZRC), Cocos-Keeling Islands , coll. P.K.L. Ng & P.J.F. Davie, 21 March 2011 ; 1 male (9.1 × 6.7 mm), 1 juvenile male, 6 females (largest 8.6 × 6.3 mm) ( ZRC), stn CK 26, lagoon side of airport near Meterological Station , West Island, Cocos-Keeling Islands, coll. P.K.L. Ng & P.J.F. Davie, 24 March 2011 ; 2 males (9.4 × 6.9 mm, 9.0 × 6.7 mm) ( QM-W28342 ), stn CK16, lagoon side of airport near Meterological Station , West Island, Cocos-Keeling Islands, coll. P.J.F. Davie & P.K.L. Ng, 22 March 2011 ; 3 males (largest 7.8 × 5.9 mm), 16 females (largest 8.7 × 6.4 mm) ( QM-W28343 ), same data QM-W28342 ; 2 males (largest 9.2 × 6.9 mm) ( QM-W28344 ), stn CK26, lagoon side of airport near Meterological Station , West Island, Cocos-Keeling Islands, coll. P.J.F. Davie & P.K.L. Ng, 24 March 2011 ; 2 males (largest 10.5 × 7.9 mm), 4 females (largest 11.4 × 8.1 mm) ( QM-W28345 ), stn CK3, Tanjong Puji , West Island, Cocos-Keeling Islands, 12°11.589’S, 96°51.549’E, coll. P.J.F. Davie & P.K.L. Ng, 20 March 2011 .

Diagnosis. Carapace 1.35–1.44 times broader than long; frontal margin bilobed, separated by broad, very shallow concavity ( Fig. 3A–C ); upper surface of cheliped palm with 2 transverse pectinate crests, primary (distalmost) crest with row of 15–18 tall pectinate teeth, tip of each tooth gently curved, secondary crest with 9 or 10 relatively lower pectinate teeth, followed by patch of 12–15 scattered low, more rounded pectinate tubercles on median part of palm ( Figs. 3H ; 7A ); inner surface of palm with low, obliquely transverse, submedian granulated ridge ( Fig. 3I ); dorsal surface of dactylus with 16–18 triangular tubercles, each dactylar tubercle with distinct transverse ridge ( Fig. 3E, F, H, I ); inner distal margin of inner lamelliform process of merus lined with sharp triangular teeth ( Fig. 3E, F, I ); ambulatory legs short, stout; merus of third leg 2.0 times as long as wide; upper margin of merus with subdistal spine; propodus of third leg 2.8 times as long as wide; dactylus of third and fourth legs 0.8 and 1.0 times length of propodus, respectively ( Figs. 3A ; 5D–G ); male telson semicircular, ca. 1.2 times length of pleonal somite 6 ( Fig. 6H ); G1 relatively slender, straight; apical process bent at 90° from the vertical, chitinous distal part long, aperture terminal ( Fig. 6I–L ).

Colour in life. Dorsal surfaces of carapace and ambulatory legs dirty white with large and small uneven patches of dark brown to grey ( Fig. 1A–C ). Chelae light orange, although ventral half darker, with dorsal parts sometimes appearing paler ( Fig. 1A–D ).

Habitat. Parasesarma sigillatum inhabits supralittoral or upper intertidal zones. It prefers a sandy substrate with some mud, and with grass growing nearby. The crabs were found hiding under flotsam, pieces of wood and small rocks. An allied species, Parasesarma cf. lenzii (De Man, 1895) can sometimes be found with it, although this species prefers muddier and wetter substrates.

Remarks. Tweedie (1950: 131) stated that one male and one female were “cotypes”, but noted that he also had 43 additional specimens. This means that only the two specimens in the NHM (labelled as cotypes) are syntypes, with the remaining material in ZRC not types. The NHM male is here designated the lectotype of Sesarma sigillata Tweedie, 1950 . There are, however, 44 specimens in a bottle in the ZRC (24 males, 20 females), not 43, suggesting that Tweedie miscounted. The two NHM specimens are in very poor condition: all the chelipeds and ambulatory legs are detached; and their carapaces are very delicate, with that of the female already medially broken. However, they agree with the ZRC specimens in all aspects, including the structure of the G1. Both G1s of the lectotype male are intact and still on the specimen, and the G1 figured by Tweedie (1950: fig. 3d) must have therefore come from one of the males in the ZRC. It was probably from the male in ZRC which has its own catalogue number (ZRC 1965.8.2.260) and a note in Tweedie’s handwriting that it was photographed; this specimen no longer has an pleon or gonopods suggesting they may have been removed for figuring and not returned to the bottle.

There is a label with the NHM material that states that this species is conspecific with “ Sesarma carolinense ”, suggesting that Serène may have examined the material before he synonymized S. carolinense with S. sigillata .

The differences between P. carolinense s. str. and P. corallicum n. sp. are outlined in the Discussion.

Figures

Fig. 1. Colour in life. A–D, Parasesarma sigillatum, Cocos-Keeling Islands; E–H, Parasesarma corallicum n. sp., Taiwan. A, male, not preserved; B, female (8.7 × 6.4 mm) (QM-W28343); C, D, male (9.4 × 6.9 mm) (QM-W28342); E, F, male, Hsiangchiaowan, Taiwan (10.3 × 7.6 mm) (NMMBCD 4698); G, Holotype, same data (9.5 × 7.0 mm) (NMMBCD 4697); H, Wanlitung, Taiwan (8.0 × 5.7 mm) (NMNS-7548-002).

Fig. 3. Parasesarma sigillatum (Tweedie, 1950). A–H, male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; I, lectotype male (10.7 × 7.6 mm) (NHM 1950.4.17.4), Cocos-Keeling Island. A, overall habitus; B, dorsal view of carapace; C, frontal view of cephalothorax; D, anterior thoracic sternum and pleon; E, dorsal view of left cheliped; F, dorsal view of right cheliped; G, outer view of right chela; H, dactylar tubercles of right chela; I, inner view of left chela.

Fig. 5. Left ambulatory legs. A–C, Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands; D–G, Parasesarma sigillatum (Tweedie, 1950), male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; H–K, Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, D, H, first ambulatory leg; B, E, I, second ambulatory leg; C, F, J, third ambulatory leg; G, K, fourth ambulatory leg. Legs of all species to scale.

Fig. 6. A–F, Parasesarma carolinense (Rathbun, 1914), holotype male (9.2 × 7.0 mm) (USNM 32861), Caroline Islands; G–M, Parasesarma sigillatum (Tweedie, 1950), male (9.5 × 6.8 mm) (ZRC 1965.8.2.269), Cocos-Keeling Island; N–T, Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. A, G, N, left third maxilliped; B, H, male pleon; O, male pleon (somites 1 and 3 broken); C, P, ventral view of left G1; D, Q, dorsal view of left G1; E, ventral view of right G1; F, distal chitinous part of right G1 (ventral view); I, ventral view of right G1; J, dorsal view of right G1; K, distal chitinous part of right G1 (ventral view); L, distal chitinous part of right G1 (dorsal view); M, right G2; R, distal chitinous part of left G1 (ventral view); S, distal chitinous part of left G1 (dorsal view); T, left G2. Setae for all structures denuded. Scale bars = 0.5 mm [A–E, G–J, M–Q, T]; 0.1 mm [F, K, L, R, S].

Fig. 7. Details of pectinate crests on chela. A, Parasesarma sigillatum (Tweedie, 1950), lectotype male (10.7 × 7.6 mm) (NHM 1950.4.17.4), Cocos-Keeling Island; B, Parasesarma corallicum n. sp., holotype male (9.5 × 7.0 mm) (NMMBCD 4697), Taiwan. Arrow points to direction of dactylar finger. Scales = 0.5 mm.