Thyroscyphus macrocyttarus (Lamouroux, 1824)

Colonies creeping, hydrorhiza tubular, undulating.

Stems arising as an extension of the hydrorhiza, either simple with a single terminal hydrotheca or erect, and bearing up to six hydrothecae. Cauline internodes long and straight, perisarc usually undulating, sometimes smooth, widening to a distal apophysis.

Hydrothecae on compound hydrocauli usually all facing the same side of stem, each borne on a very short, narrow pedicel from the stem apophysis. Hydrothecae very large, campanulate, expanding evenly from base to margin, the hydranth supported on a distinct, flattened shelf above base. Margin circular to somewhat quadrangular, with heavily thickened rim, a deeply indented submarginal ring below margin and four equidistant low, blunt marginal teeth. A low operculum of four equal triangular valves present in young hydrothecae.

Hydranth very large and robust with about 20 short, stubby tentacles.

Gonotheca borne on a short pedicel arising from the internode immediately below the hydrothecal apophysis, barrel-shaped, often asymmetrical with one side more convex than the other, walls broadly undulating, maximum diameter just below mid-region, distal end truncated, summit often depressed, without aperture. Female gonophore a fixed sporosac containing two or three large ova surmounted by a plug of tissue. Male gonophore unknown.

Colour: Perisarc brown, hydranth often yellow; colony frequently overgrown by pink crustose coralline algae.