Bugula flabellata forms an erect, densely tufted, branched colony about 2-5 cm in height and is a buff colour when living, grey when dried. The branches are broad, flat and wedge-shaped, and composed of rows of four or more zooids, somewhat circularly disposed. Individual zooids are rectangular in shape and 0.5-0.8 x 0.2 mm. Zooids at the margin of the branches bear 3 spines on the outer distal corner and 2 on the inner distal corner. Inner zooids bear 2 spines on each distal corner. The front of the zooid is almost entirely membranous. The polypide has 14 tentacles. Avicularia are present on inner and marginal zooids, being larger on the latter, with the beak hooked rectangularly. Brood chambers (ooecia) are sub-globular and conspicuous. Colonies are attached to the substratum by extensions of the basal zooids termed rhizoids. Yellow embryos are present from early May to October. The newly settled larvae form ancestrula with 3 proximal spines and 3 spines on each distal angle.