Lytocarpia brevirostris (Busk, 1852)

Hydrorhiza a stout tube from which stems arise at intervals. Stems short, pinnate, to 10–15 mm high, proximal part of stem ahydrocladiate, some with a supplementary fascicular tube running part way up stem. Stem internodes short, nodes poorly defined, transverse to slightly oblique; hydrocladia alternate, about 2 mm long, 1 per stem internode, inserted on a short apophysis on front of stem; a small open pore (mamelon) on base of apophysis.

Hydrocladial internodes long, base of each strongly displaced with respect to next one, node present, indistinct or absent at point of displacement, internode with 1 complete septum beneath posterior quarter of hydrotheca and another, partial, below saddle in hydrotheca.

Hydrotheca elongate, parallel with internode, margin separated from mesial nematotheca by deep saddle; margin sloping forward with a long, sinuously curved, blunt anterior cusp, followed by 3 pairs of deeply incised, sharply pointed cusps, the third pair usually obscured by lateral nematothecae; base of hydrotheca with a short, forwardly pointing intrathecal septum.

Mesial hydrothecal nematotheca rather short, digitate, at an angle of about 50° to internode, apex about level with anterior hydrothecal cusp, orifice small, shallowly canaliculate; lateral nematotheca flask-shaped, laying almost parallel to internode, orifice small, canaliculate down to internode. Two cauline nematothecae, one above and one below hydrocladial apophysis; same shape as laterals, but base a little more inflated, orifice of upper facing away from apophysis, orifice of lower facing up and outwards.

Colour: yellow.