A Gram-negative, strictly anaerobic, halophilic, motile, sporulating and rod-shaped bacterium, designated strain HY-42-06T, was isolated from tidal flat sediment from Ganghwa Island in South Korea. The isolate produced glycerol, ethanol and CO2 as fermentation end-products from glucose. Strain HY-42-06T grew optimally at 35 degrees C, pH 7.5 and 3 % (w/v) artificial sea salts. No growth was observed in the absence of sea salts. In phylogenetic analyses based on 16S rRNA gene sequence, strain HY-42-06T showed a distinct phyletic line within the members of cluster I of the order Clostridiales. The closest phylogenetic neighbour to strain HY-42-06T was Clostridium novyi ATCC 17861T (94.91 % 16S rRNA gene sequence similarity). Several phenotypic characters readily differentiate the tidal flat isolate from phylogenetically related clostridia. On the basis of polyphasic evidence, strain HY-42-06T should be classified as a representative of a novel species, for which the name Clostridium ganghwense sp. nov. is proposed. The type strain is HY-42-06T (=IMSNU 40127T = KCTC 5146T = JCM 13193T).