Pseudosesarma edwardsii (De Man, 1887 )

Ng, Peter K. L. & Schubart, Christoph D., 2017, On the taxonomy of Pseudosesarma edwardsii (De Man, 1887) and P. crassimanum (De Man, 1887) (Crustacea: Decapoda: Brachyura: Sesarmidae), with description of a new species from Sri Lanka, Raffles Bulletin of Zoology 65, pp. 655-669 : 655-661

publication ID	https://doi.org/ 10.5281/zenodo.13256838
publication LSID	lsid:zoobank.org:pub:345579E6-E31B-4093-A731-813296EC1F77
persistent identifier	https://treatment.plazi.org/id/03D3D81E-A152-FFFD-8280-68955F8CF9E8
treatment provided by	Felipe
scientific name	Pseudosesarma edwardsii (De Man, 1887 )
status

Treatment

Pseudosesarma edwardsii (De Man, 1887) View in CoL

( Figs. 1A–C View Fig , 2A, B View Fig , 3–7 View Fig View Fig View Fig View Fig 6 View Fig , 12 View Fig )

Sesarma edwardsii De Man, 1887: 649 View in CoL .

Sesarma edwardsi View in CoL – De Man, 1888: 185, pl. 13 figs. 1–4; Lanchester, 1900: 757.

Sesarma (Sesarma) edwardsi View in CoL – Tesch, 1917: 147 (part?).

Sesarma (Sesarma) edwarsi (sic) – Serène, 1968: 105.

Pseudosesarma edwarsi (sic) – Serène & Soh, 1970: 399, 406.

Pseudosesarma edwardsii View in CoL – Fransen et al., 1997: 127; Ng et al., 2008: 222.

Not Sesarma edwardsi Ortmann, 1894: 721 View in CoL = Bresedium brevipes (De Man, 1889) View in CoL .

Material examined. Lectotype (here designated), male (17.5 × 16.1 mm) ( NNM-D17 a), Mergui Archipelago, Myanmar, coll. J. Anderson, 1886 . Paralectotypes: 1 female (NNM- D17b), same data as lectotype; 1 young male (7.9 × 7.0 mm) , 8 females (20.3 × 17.7 mm, 14.9 × 13.2 mm, 13.8 × 12.7 mm, 13.7 × 12.5 mm, 12.3 × 11.6 mm, 12.3 × 11.3 mm, 10.9 × 10.2 mm, 8.8 × 7.9 mm) ( NHM 1886.52 a), same data as lectotype. Others: SINGAPORE – 1 male (19.4 × 17.3 mm) ( ZRC 1971.9.24.8), Sungei Seletar , coll. C.L. Soh, 29 March 1966 ; 1 male ( ZRC 1965.7.29.50), Pulau Aya , Merban, coll. F.N. Chasen, 1931 ; 1 male ( ZRC 1971.9.24.9), Sungei Seletar , coll. C.L. Soh, 29 March 1966 ; 1 male ( ZRC 2003.0083 View Materials ), Pulau Ubin , vicinity of Asam mangroves (pitfall trap), coll. R. Teo, 20 September 2001 ; 1 male, 1 female ( ZRC 2000.2019 View Materials ), Pulau Ubin , coll. C.D. Schubart, July 2000 ; 3 males ( ZRC), swamp along dirt road to Chek Jawa , Pulau Ubin, coll. C.D. Schubart, 25 November 2011 ; 1 male ( ZRC 2003.0084 View Materials ), culvert beside reservoir, Pulau Tekong , Singapore, coll. B.Y. Lee, 16 November 2001 ; 1 female (11.5 × 10.0 mm) ( ZRC 2013.1116 View Materials ), near stream, northern axis of Pulau Tekong , coll. T.M. Leong, 31 January 2002 ; 1 ex-ovigerous female (19.1 × 17.8 mm, first zoeae reared and preserved) ( ZRC 2017.1053 View Materials ), in secondary forest, 300 m from coast, coll. M. Chua, 24 March 2012 . PENINSULAR MALAYSIA – 1 male ( ZRC 1984.8031 View Materials ), Pangkor Island , Straits of Malacca, coll. 13 August 1967 ; 1 male, 1 female ( ZRC 2010.0035 View Materials ), Pulau Langkawi , Temurun waterfall, coll. P.K.L. Ng, 17 June 1998 ; 1 male (13.9 × 12.9 mm), 1 female (13.1 × 11.6 mm) ( ZRC), Sungei Temurun Datai , Langkawi, Kedah, Malaysia, coll. Universiti Sains Malaysia, 1 April 2003 ; 1 male (19.4 × 18.2 mm), 1 female (19.3 × 17.7 mm) ( SMF) Pulau Langkawi , Air Temurun waterfall and stream, coll. C.D. Schubart et al., 15 March 2006 .

Diagnosis. Carapace almost quadrate ( Figs. 1A View Fig , 2A View Fig , 3 View Fig ); frontal margin relatively wide, median concavity separating lobes shallow ( Fig. 2A View Fig ); epibranchial tooth distinct, separated from rest of margin by deep notch ( Figs. 1A View Fig , 2A View Fig , 3 View Fig ); posterolateral margins slightly divergent to subparallel posteriorly ( Figs. 1A View Fig , 2A View Fig , 3 View Fig ); outer surface of chela gently convex, covered with small rounded granules, ventral margin of palm sinuous, unarmed or with low granules, fingers relatively long compared to overall chela ( Figs. 1B View Fig , 4 View Fig , 12D, E, G View Fig ); suture between male thoracic sternites 3 and 4 distinct ( Figs. 5 View Fig , 6C View Fig 6 ); male pleon broadly triangular ( Figs. 1C View Fig , 5 View Fig , 6A, B View Fig 6 ); male sternopleonal cavity with press-button of pleonal locking mechanism on sternite 5; G1 very stout, lateral margins parallel, distal part distinctly bifurcated or bilobed, with short subtruncate chitinous part between lobes ( Figs. 6D, E View Fig 6 , 7A, B, D–I View Fig ).

Colour. Brown to reddish-brown in life, with many specimens having the posterior part of the carapace slightly to distinctly darker in colour ( Fig. 12A, C, F, G View Fig ). In life, the chelae are red to dark red, with the pigmentation extending to midway or further along the finger and the distal part white ( Fig. 12D, E, G View Fig ).

Remarks. The situation regarding the date of publication for Sesarma edwardsii is the same as that discussed for Sesarma polita De Man, 1887 [now Labuanium politum (De Man, 1887) ] by Ng et al. (2015: 217). De Man (1887: 649) had credited the name to “De Man. 1886”, but this paper was not published until 1888. Although De Man (1888: 185) cited the species as new, the name was already available from his 1887 paper, and the species should be dated from then. In his 1887 paper, De Man did not indicate how many specimens he examined, but later (De Man, 1888) listed 58 specimens from Sullivan Island in the Mergui Archipelago. Although he noted the largest male and female specimens as measuring 20.33 × 18.67 mm and 19.50 × 17.33 mm, respectively (De Man, 1888: 188), no type was designated. Fransen et al. (1997: 127) listed a male and a female specimen as syntypes; and the male is here designated as the lectotype of Sesarma edwardsii De Man, 1887 . The NHM has one small male and eight females (NHM 1886.52a) but the whereabouts of the remaining specimens are not known. On a point of nomenclature, De Man (1887: 649) originally spelled the names as “ Sesarma edwardsii ” but later used only one “i” for the name, “ Sesarma edwardsi ” (cf. De Man, 1888: 185). The original spelling is here maintained.

The male pleon in P. edwardsii varies to some degree according to size. In the largest males (carapace width ca. 20 mm) and lectotype from Mergui (17.5 × 16.1 mm, NNM-D17), the pleon (notably somites 3–6) is wider ( Figs. 1C View Fig , 6A View Fig 6 ), being less so in smaller males ( Figs. 5E, F View Fig , 6B View Fig 6 ). The G1 structure does not change substantially in form from small and large specimens ( Figs. 6D, E View Fig 6 , 7A, B, D–I View Fig ), although juvenile males (less than 10 mm carapace width) have a less chitinised structure.

Pseudosesarma edwardsii and P. crassimanum (De Man, 1887) are closely related and not always easy to separate. They have been generally regarded as varieties in many of the earlier works but De Man (1888: 188–189) distinguished P. crassimanum from P. edwardsii as follows: “The front is a little larger, the proportion of the distance between the extraorbital teeth to the breadth of the front being as 11: 7 [11: 6 in P. edwardsii ]; the abdomen of the male is a little less enlarged, and therefore completely resembles the abdomen of S. picta , as figured by de Haan, the posterior margin of the penultimate joint being a little less than three times as broad as the length of the joint. The hands of the male differ from those of the type by the palm being a little larger in proportion to the fingers, the latter being quite as long as the palm. The hands are a little, higher than half length, the proportion of the latter to the height being as 16½: 9½. The inner edges of the fingers are more strongly denticulated, the immobile finger being armed with three rather strong teeth, and with some smaller teeth at the base. The colouration of the hands is also somewhat different from the type. In the latter the red colour of the palm extends nearly to the tip of the fingers; but in this variety that colour is found only on the palm and at the base of the mobile finger, the fingers being of a yellowish colour.” De Man (1887, 1888) obviously felt the differences were not substantial as he treated P. crassimanum only as a variety. De Man (1888) did not figure the carapace of P. crassimanum , only its male pleon and chela ( Fig. 1D, E View Fig ), and these agree with the description above.

Certainly, the difference in male pleon shape is apparent, when large specimens of both species are compared, with that of P. crassimanum always relatively more slender, with somites 3–5 proportionately less broad ( Figs. 1E View Fig , 10 View Fig ). Even the largest specimen of P. crassimanum examined ( Fig. 10B View Fig ) does not have a male pleon as wide as those of large adult P. edwardsii ( Fig. 5A, B View Fig ). Smaller specimens of P. edwardsii , however, may have male pleons ( Fig. 5E, F View Fig ) which resemble those of adult P. crassimanum ( Fig. 10 View Fig ). As discussed earlier, the different male pleonal structures, notably in the relative width of somite 6, may be a function of size, but the largest male of P. crassimanum that De Man had measured (19.25 × 17.25 mm, see De Man, 1888: 189) is not markedly different from the largest male of P. edwardsii that he examined (20.33 × 18.67 mm). The male chela of P. crassimanum figured ( Fig. 1D View Fig ; De Man, 1888: pl. 13 fig. 6) is notably stouter, with the chela relatively shorter (hence De Man’s name for the taxon) and the ventral margin relatively more denticulate compared to that of P. edwardsii ( Fig. 1B View Fig ; De Man, 1888: pl. 13 fig. 3). This is also valid for the good series of specimens of P. crassimanum here examined ( Fig. 9 View Fig ), when compared to the chelae of P. edwardsii ( Fig. 4 View Fig ).

Specimens from western Thailand, Malaysia, Singapore and Kalimantan have mainly been identified as P. crassimanum based on the description and figures provided by De Man (1887, 1888). The frontal margin of P. crassimanum appears to be relatively wider than that of P. edwardsii , mainly because the carapace shape of P. crassimanum is more transversely rectangular ( Figs. 3C View Fig , 8 View Fig ) compared to the more quadrate shape of P. edwardsii ( Figs. 1A View Fig , 2A View Fig , 3 View Fig ). This difference, however, is not always reliable, being less obvious in small specimens. De Man (1888) notes that the cutting margins of the fingers are more denticulate with stronger teeth in P. crassimanum compared to P. edwardsii . All the cutting edges of the fingers of adult male P. crassimanum have proportionately much stronger teeth ( Fig. 9 View Fig ) than those of P. edwardsii ( Fig. 4 View Fig ). In addition, the figure of the chela by De Man of P. crassimanum ( Fig. 1D View Fig ; De Man, 1888: pl. 13 fig. 6) shows a distinct large subproximal tooth on the cutting margin of the dactylus. This large tooth is absent in P. edwardsii , the subproximal part of the cutting margin of the dactylus possessing about three small teeth instead ( Fig. 11B–F, H–L, O–R View Fig ). The carapace also appears to be differently coloured in life. In P. edwardsii , most of the specimens have the posterior part of the carapace relatively darker in colour, to the degree that it appears bicoloured ( Fig. 12C, F View Fig ). In P. crassimanum , the dorsal surface of the carapace is usually more uniformly coloured brown, although the posterior part is often darker ( Fig. 13A, C, F View Fig ).

( Fig. 1B View Fig ; De Man, 1888: pl. 13 fig. 3). This subproximal dactylar tooth is present in all the adult male chelae of the material of P. crassimanum examined here. As such, the general form of the chela, as well as the dentition of the fingers, are surprisingly reliable diagnostic characters for P. crassimanum . De Man (1888) was also correct about the colour of the chela in life. In fresh P. edwardsii , the red colour on the chela extends to the middle to three-quarters of the length of both fingers, with the distal half white ( Fig. 12D, E, G View Fig ). In P. crassimanum , the more reddish colour on the chela ends at the bases of both yellowish-white fingers ( Fig. 13B, D, H, I View Fig ).

Another difference between P. crassimanum and P. edwardsii is the form of the frontal margin. The median concavity separating the two lobes is usually more distinct in P. crassimanum ( Figs. 2C View Fig ) than in P. edwardsii ( Figs. 2A View Fig ). The adult ambulatory leg of P. crassimanum , notably the merus, are also usually proportionately shorter ( Fig. 8 View Fig ) compared to those of P. edwardsii ( Fig. 3 View Fig ), although this character is not reliable for subadults. The most effective character to separate the two species is the G1. In P. edwardsii , the G1 is evenly stout, with the margins parallel, and the distal part bifurcated or bilobed, with the chitinous part between the lobes short ( Figs. 6D, E View Fig 6 , 7A, B, D–I View Fig ). In P. crassimanum , the distal half of the G1 is much wider than the proximal part, and the chitinous distal part forms a beak-like structure “ Sesarma edwardsi ” and “ Pseudosesarma edwardsii ” have been reported from many parts of Burma, India, Andamans, Bangladesh, Sri Lanka by Alcock (1900: 416), Mandal & Nandi (1989: 25), Kathirasan (2000: 193), Dev Roy & Nandi (2001: 18), Dev Roy & Bhadra (2007: 143, pl. 4 fig. 5), Dev Roy (2008: 131), Paul et al. (2012: 193), Holmes et al. (2014: 160) and Shet et al. (2016: 8, 12, fig. 2); as well as Java, Sulawesi and New Guinea by Tesch (1917: 147). The material from Sri Lanka by Alcock (1900) is probably conspecific with what is described later as P. anteactum , new species. Specimens from Kerala in West India which are superficially similar to P. edwardsii have been referred to a new species, P. glabrum (cf. Ng et al., 2017), and many of the western Indian records are probably conspecific with it. Ng (2017) also recently described a species morphologically similar to P. crassimanum from Myanmar. The identities of the others can only be ascertained when the specimens are re-examined. Some may belong to P. crassimanum or another sesarmid species. The record of “ Sesarma edwardsi ” by Ortmann (1894: 721) from Australia is probably what is now known as Bresedium brevipes (De Man, 1889) (see also Laurie, 1906; McNeill, 1968).

Biology. Pseudosesarma edwardsii is typically found in well forested lowland freshwater or brackish water habitats behind of coastal areas and seashores. They are semiterrestrial living at the banks of streams and swamps, and are often found under rocks and vegetation. They are sometimes several hundred metres from the sea, even at the base of waterfalls. They have small eggs ( Fig. 12B View Fig ) and it is clear that their larval development remains associated to the open sea and as such, they belong to the supratidal-limnic life form as characterised by Schubart et al. (2000).

Distribution. Mergui Archipelago to Peninsular Malaysia and Singapore for certain; other records need to be confirmed.