Sertularella diaphana (Allman, 1885)

Stems to 100 mm high, pinnately branched in one plane, lower stem thick, fascicled, polysiphonic tubes a continuation of hydrorhizal filaments, stems becoming monosiphonic distally. Stem internodes short, broad, nodes transverse to slightly oblique, sometimes indistinct.

Hydrocladia distal on cauline internodes, three hydrothecae on internode, one below hydrocladium, one in, or in front of axil and one opposite, axillar hydrothecae adnate to caulus and of same shape as others. Hydrocladia alternate, on indistinct apophysis, proximal part fairly long, slender, athecate, the first hydrotheca on basal side of hydrocladium.

Hydrothecae alternate, immersed in internode, short, widely separated laterally, base of each reaching about halfway up wall of that opposite, widest in proximal third, adcauline wall convexly curved, a small knot of perisarc at base, floor a downwardly tilted shelf, abcauline wall straight to slightly concave, contiguous with hydrotheca below. Margin subcircular in frontal view, tilted upwards at angle of 45°- 60° to hydrocladial axis, rim distinctly thickened with four equidistant, low rounded cusps, one abcauline, one adcauline and two lateral, separated by shallow embayments, no replication of margin, operculum of four fairly thick triangular flaps.

Hydranth with deep abcauline caecum and about 20 tentacles.

Gonothecae borne on stem and hydrocladia, inserted without pedicel below a hydrotheca, a circular foramen connecting with hydrocladium; gonotheca elongate conical, adpressed to hydrocladium, perisarc thick, most with several longitudinal pleats, some indistinctly undulated.

Colour: Orange to honey brown.