Gymnangium gracilicaule (Jäderholm, 1903)

Stems lightly fascicled, with 3 - 8 fascicular tubes, hydrorhiza comprising an extension of the fascicular tubes. Branches given off pinnately at approximately 45" from a secondary fascicular tube behind anterior tube, branches extending from near base of the stem to distal end of the hydrocaulus. Near proximal end of stem, secondary cauline hydrocladia arise directly from the anterior fascicular tube, these strictly alternate, 4 - 6 between each primary branch, recurved backwards around stem, each bearing 2 - 8 hydrothecae; these secondary hydrocladia extending to distal end of the colony. Proximal region of branches ahydrocladiate, bearing nematocysts in groups of three, similar to those on proximal part of the branch.

Hydrocladia given off front of the branch, internodes short, straight, nodes transverse, constricted, with two internal septa, one connecting with the intrathecal septum, the other below the median nematotheca.

Hydrotheca occupying entire internode, sigmoidally curved, an intrathecal septum passing vertically into the hydrotheca from the floor almost to base of the median nematotheca, abcauline hydrothecal wall sometimes thickened behind margin. Margin everted, edentulate or with suggestion of a lateral lobe, some margins slightly thickened anteriorly.

Median nematotheca short, not extending beyond hydrothecal margin, free part almost straight, narrowing distally, with three orifices - a small terminal orifice, a slightly larger subterminal orifice immediately above abcauline hydrothecal wall and an orifice into the hydrotheca. Twin lateral nematothecae tubular, abcauline walls convex, adcauline walls straight or slightly concave, extending forward and outward beyond hydrothecal margin, narrowing to a small round terminal orifice. Anterior fascicular tube on stem with a longitudinal row of closely approximate nematothecae; two cauline nematothecae present beside the apophysis of branch, one on apophysis and one just above, the proximal one similar to median hydrothecal nematotheca but truncated, the terminal and subterminal orifices almost coincident; distal nematotheca similar to hydrothecal laterals.

Colour: Fascicular tubes glistening honey brown, hydrocladia white.