A novel unicellular red alga collected from a mangrove area on Iriomote Island in southwest Japan is described as Bulboplastis apyrenoidosa gen. et sp. nov. The cells are spherical, mean 11.2 µm in diameter, and surrounded by a thick mucilaginous sheath. The grayish-green chloroplast has many lobes extending throughout the cell and lacks a pyrenoid. This chloroplast type is similar to Glaucosphaera vacuolata, but differs from other unicellular red algae. Plastoglobuli clusters occur beneath the chloroplast envelope but only at the cell periphery. A peripheral encircling thylakoid is absent. Golgi bodies surround the central nucleus, which is an arrangement shared with all members of the Dixoniellales. The subcellular features of some mitotic phases are quite similar to those of other unicellular red algae. A pair of ring-shaped structures located within electron-dense material can be seen in cells undergoing telophase. The size of the polar rings ranged within those reported from the Dixoniellales. A phylogenetic analysis based on small subunit rDNA indicates that B. apyrenoidosa is a member of the Dixoniellales and a sister lineage to Neorhodellaand Dixoniella.