A bacterial strain, designated NSW-5(T), was isolated from a water sample taken from Niao-Song Wetland Park in Taiwan and characterized using a polyphasic taxonomic approach. Cells of strain NSW-5(T) were strictly aerobic, Gram-stain-negative, non-motile and polymorphic, being straight, vibrioid, curved and spiral-shaped rods surrounded by a thick capsule and forming light pink-coloured colonies. Some rings consisting of several cells were present. Growth occurred at 10-40 �XC (optimum, 25 �XC), with 0-3.0 % NaCl (optimum, 0 %) and at pH 6.0-8.0 (optimum, pH 7.0). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain NSW-5(T) belonged to the genus Arcicella with sequence similarities of 98.6, 98.0 and 97.3 % with Arcicella aquatica NO-502(T), Arcicella rosea TW5(T) and Arcicella aurantiaca TNR-18(T), respectively. The predominant cellular fatty acids were summed feature 3 (C(16 : 1)�s7c and/or C(16 : 1)�s6c; 20.8 %), C(16 : 0) (14.6 %), iso-C(15 : 0) (13.8 %), C(16 : 1)�s5c (12.5 %) and C(18 : 0) (11.4 %), and the only respiratory quinone was MK-7. The polar lipid profile consisted of phosphatidylethanolamine and several uncharacterized glycolipids, aminolipids, phospholipids and aminophospholipids. The DNA G+C content of strain NSW-5(T) was 44.1 mol%. The DNA-DNA relatedness of strain NSW-5(T) with respect to recognized species of the genus Arcicella was less than 70 %. On the basis of phylogenetic inference and phenotypic data, strain NSW-5(T) should be classified as a representative of a novel species, for which the name Arcicella rigui sp. nov. is proposed. The type strain is NSW-5(T) (= KCTC 23307(T) = BCRC 80260(T)). Emended descriptions of the genus Arcicella and of Arcicella aquatica, Arcicella rosea and Arcicella aurantiaca are also proposed.