The growth form is variable (see General biology) from thinly to massively encrusting, with tassel-like irregular branches which form flattened masses. Colonies can be up to 25 cm across with branches reaching 12 cm high. Its colour is beige to dull brown in the summer, and light grey/yellow in the winter. Halichondria bowerbanki
typically turns a characteristic yellow-orange when spawning because of the colour of the larvae. There are no obvious large exhalent openings (oscules) present and the surface is smooth or uneven with a breadcrumb-like texture.
- Microscopic examination of the spicules reveals that they are relatively long and thin, and taper to the apices.
- Named after James S. Bowerbank (1797-1877), a pioneering authority on sponges.
- Easily confused with Halichondria panicea but Halichondria bowerbanki is distinguished by the absence of the chimney-like oscules that occur in Halichondria panicea.