Gymnangium hians (Busk, 1852)

Hydrorhiza ramified, stems unbranched, up to 40 mm long, stiffly plumose, monosiphonic, proximal stem wide, prosegment bearing remnant spurs from shed hydrocladia; stem narrowing distally, perisarc thick and shining. Cauline nodes transverse, faint to distinct, hydrocladia alternate, on opposite sides of stem, directed upwards at an angle of c. 45° to axis, slightly recurved, usually two, sometimes one on internode; hydrocladia up to 20 mm long, internodes deep, nodes slightly oblique, faint, no intranodal septa.

Hydrothecae saccate, contorted about middle, floor convex, proximal part of wall sometimes extended downwards into a knot of perisarc, free adcauline wall short, straight to slightly convex, abcauline wall completely adnate to mesial nematotheca, a thick hook-shaped intrathecal septum passing forward into hydrotheca from mid-abcauline wall, free end of septum a ragged edge (anterior view). Margin tilted upwards, a pair of sharply pointed, posteriorly pointing cusps in posterior third , margin strongly everted into pair of broad cusps, a pair of small cusps between lateral nematothecae, rarely a second pair of small, poorly defined cusps between these and lateral cusps.

Mesial nematotheca narrowing from base to apex, free part long, arching over hydrotheca, abcauline wall thickened, terminal orifice circular, a small secondary orifice just above junction with hydrotheca. Lateral nematothecae short, saccate, tubular, orifice large, open down to hydrothecal margin. Cauline nematothecae same as laterals, one above and one below hydrocladial apophysis and one behind axil.

Gonothecae conical, perisarc thin, in a single crowded row along stem.

Colour: Stem shining dark brown, hydrocladia and gonothecae paler brown to cream.