A Gram-negative, chemoheterotrophic, facultatively anaerobic coccus, designated IMCC1545(T), was isolated from the digestive tract of a marine clamworm, Periserrula leucophryna, inhabiting a tidal flat of the Yellow Sea. Cells of strain IMCC1545(T) are non-motile, dividing by binary fission. The predominant fatty acids are anteiso-C(15 : 0) and C(18 : 0). The respiratory quinone is menaquinone-7 and the DNA G+C content is 52.1 mol%. Phylogenetic analyses based on 16S rRNA gene sequences using three treeing algorithms revealed that the strain formed a novel genus-level lineage within the phylum 'Verrucomicrobia'. The most closely related named organisms to strain IMCC1545(T) are 'Fucophilus fucoidanolyticus' SI-1234 (86.5 % 16S rRNA gene sequence similarity), Alterococcus agarolyticus ADT3(T) (81.8 %) and Opitutus terrae PB90-1(T) (80.3 %), which belong to subdivision 4 of the 'Verrucomicrobia'. Subdivision 4 of the 'Verrucomicrobia' (here named Opitutae classis nov.) was divided into two clades, a clade containing strain IMCC1545(T) and a clade containing Opitutus terrae. From the taxonomic data obtained in this study, it is proposed that the new marine isolate be placed into a novel genus and species named Puniceicoccus vermicola gen. nov., sp. nov. (the type strain of Puniceicoccus vermicola is IMCC1545(T)=KCCM 42343(T)=NBRC 101964(T)) within Puniceicoccaceae fam. nov and Puniceicoccales ord. nov in the class Opitutae. The family Opitutaceae fam. nov. and order Opitutales ord. nov. are also formally proposed.