Exagorium fidelisi Naruse, Chung & Tangah, 2015

Mendoza, Jose Christopher E., 2021, Marine crabs new to Singapore, with a description of a new species of intertidal xanthid crab of the genus Macromedaeus Ward, 1942 (Crustacea: Decapoda: Brachyura), Raffles Bulletin of Zoology 69, pp. 463-480 : 465

Exagorium fidelisi Naruse, Chung & Tangah, 2015

( Fig. 1 )

Exagorium fidelisi Naruse et al., 2015: 328 , figs. 1, 2, 3a, 4, 5 (type locality: Sabah, Malaysia).

Material examined. 2 males, 8.5 × 6.0 mm, 8.7 × 6.1 mm, 1 ovig. female, 9.0× 6.7 mm ( ZRC 2019.0662 ), Singapore, Sungei Buloh Wetland Reserve , back mangrove, in soft mud, under wooden plank, coll. Tan H. H. et al., 9 February 2017 .

Remarks. The camptandriid genus Exagorium Naruse, Chung & Tangah, 2015 , is currently represented only by the type species, E. fidelisi Naruse, Chung & Tanagah, 2015 , which was discovered in the estuarine habitats of Tundon Buhangin, Lower Kinabatangan-Segama Wetlands, in Sabah, Malaysia, near the northeastern tip of Borneo. It is distinguishable from other mangrove camptandriid crabs by its hexagonal carapace with cristate anterolateral margins, pale ivory colouration, male pleon which completely conceals the G1, thin pleonal somite 1 which partially covers the P5 coxa, and slender, recurved, terminally bifurcate G1 ( Naruse et al., 2015).

The present material ( Fig. 1 ) agrees well with the type series (cf. Naruse et al., 2015: figs. 1, 2, 3a, 4, 5), and there is no doubt that they are conspecific. The habitat of E. fidelisi in Singapore is slightly different from that of the type locality. The present material was collected from the back mangrove zone dominated by Bruguiera spp. (Tan H. H., pers. comm.), while the type material was collected from a muddy riverbank dominated by nipa palms. The collecting method is also different—the present material was picked by hand from beneath a wooden plank that had been laid on top of the soft mud (Tan H. H., pers. comm.), whereas the type material was collected from submerged mud burrows by yabby pump. The three specimens (two males and one ovigerous female) were collected with other camptandriid crabs, Ilyogynnis microcheirum ( Tweedie, 1937) and Paracleistostoma depressum De Man, 1895 (both of which were more abundant). The presence of E. fidelisi in Singapore is perhaps not surprising considering its relative proximity to the type locality in Sabah, eastern Malaysia. It is, however, important to note that this species has eluded previous surveys of the mangroves of Singapore, and does not appear in published accounts of Singapore’s ocypodoid crab fauna (e.g., Tweedie, 1937; Tan & Ng, 1994). The probable reason is that while the present habitat in which E. fidelisi was found, the Sungei Buloh Wetland Reserve, has been extensively surveyed, the survey methods used then did not specifically target deeply burrowing infauna (contrasted to the use of a yabby pump by Naruse et al., 2015). The present specimens, therefore, were found serendipitously. This is the first published record of E. fidelisi from Singapore and only the second time it has been recorded since it was described by Naruse et al. (2015).

Figures

Fig. 1. Exagorium fidelisi Naruse, Chung & Tangah, 2015 (ZRC 2019.0662), Sungei Buloh Wetland Reserve, Singapore. A, male, 8.5 × 6.0 mm; B–G, male, 8.7 × 6.1 mm; H, I, ovig. female, 9.0 × 6.7 mm. A, H, habitus, dorsal view; B, cephalothorax, anterior view; C, male thoracic sternum and pleon; D, eyes, antennae, and third maxillipeds, anteroventral view; E, left chela, external view; F, left G1, sternal view; G, left G1, pleonal view; I, cephalothorax and pleon, ventral view. Scale bars: A, H = 5.0 mm; B–E, I = 1.0 mm; F, G = 0.5 mm.