Arcotheres sp., a new report on pea crabs (crustacea: pinnotheridae) in bivalves from the setiu wetland lagoon, malaysia

Pea crab infestations reduce the quality of bivalves, decreasing their market value and may result in consignment rejection during exportation in the bivalve aquaculture industry. This study investigates the prevalence of pea crabs in four different species of bivalves collected in habitats in the Setiu Wetland Lagoon, Terengganu. A total of 771 samples of bivalves including Geloina expansa (Mousson, 1849), Meretrix meretrix (Linnaeus, 1758), Anadara cornea (Reeve, 1844) and Magallana bilineata (Röding, 1798) were collected during low tide, with shell length measurements of 5.44 ± 1.3, 2.67 ± 0.6, 3.96 ± 0.6 and 0.00 ± 0.0, respectively. No length measurement was recorded for M. bilineata due to the unequal sizes of the shells. A total of 30 pea crabs were harboured with single colonisation and all of them were females. The pea crabs were identified to be from the genus Arcotheres sp. Manning, 1993 with carapace subcircular and invisible eyes in the dorsal view, chela slender, half of the palm length dactylus, palm slender, dactylus and pollex straight, propodus spatulate with apex rounded, dorsally and distally setose, slender exopod, dorsally and ventrally unarmed ambulatory legs, and relative length of meri P3>P2=P4>P5, P2 and P3 dactyl less than half of the propodal length. The prevalence of pea crabs was higher in G. expansa (P: 9.73%), followed by M. bilineata (P: 1.59%) and M. meretrix (P: 1.12%) which were highly influenced by the host size. No pea crab infestation was found in A. cornea probably due to muddy and strong waves area. Overall, the present study revealed that host size and habitat were the main factors affecting the colonisation of pea crabs in bivalves from the Setiu Wetland Lagoon, Terengganu.