Diphasia mutulata (Busk, 1852)

Colonies of simple stems to 10 mm high arising at intervals from tubular hydrorhizae creeping on host; stems unbranched, proximal stem region variable in length, tubular, athecate, perisarc smooth, ending in a strong hinge joint.

Hydrothecae biseriate, paired, sometimes in contact, one pair on internode, nodes transverse, indistinct or absent. Two distinct kinds of stems, each with differently shaped hydrothecae morphologically similar to Diphasia mutulata and D. heurteli occur in the colony.

Diphasia mutulata morph: tubular, adcauline wall sinuous, often a distinct hump in mid-region, free adcauline wall one quarter to one third length of adnate wall; abcauline wall concave to sinuous, deflected outwards, sometimes an internal shelf of perisarc well below margin; margin large, shovel-shaped, facing upwards, operculum dome-shaped, perisarc very delicate, often collapsed into hydrotheca.

Diphasia heurteli morph: tubular, long, narrow at base, expanding a little to margin, adnate adcauline wall convex, free part concave, c. half adcauline wall free; abcauline wall concave, a long upwardly pointed internal shelf about two-thirds distance up wall; margin facing upwards almost perpendicular to cauline axis with a pair of low lateral lobes, operculum usually collapsed inwards, perisarc delicate.

Gonothecae monoseriate and closely adpressed to hydrocaulus, one between each hydrothecal pair on a short, wide, pedicel; gonotheca ovoid, body covered in irregular rows of short, thick, distally-facing spines, distal orifice a small tube surrounded by spines.

Colour: Pale shining brown.