Characters: Colonies are free-living, circular in outline and are flat or form a central dome. Most colonies are regenerated from fragments and thus have a central area of parallel septo-costae (the original fragment) surrounded by a border of peripheral septo-costae which are perpendicular to the margin. Mouths are distinctive in the central area, but are small or absent in peripheral areas. Septo-costae are in two or three orders. Septal spines are tall with elaborated teeth.

Colour: Grey-brown. Mouths are not distinctively coloured.

Similar Species: Halomitra pileus, which may have a similar growth-form but is distinctly coloured, has more mouths, and has smooth septal spines. See also H. clavator, which is relatively fragile, is usually attached, and has distinctive orders of septo-costae.

Habitat: Sheltered habitats.

Abundance: Rare.