Macrorhynchia filamentosa (Lamarck, 1816)

Stems lightly fascicled, branches and cauline hydrocladia given off from anterior tube; a row of nematothecae on front of the stem. Branching pinnate, with one or two fascicular tubes running along the branches. Branch internodes wide, nodes slightly oblique, obscure proximally, becoming more distinct distally along the branch, proximal quarter to one third of branch ahydrocladiate but with a row of nematothecae along the primary tube and a pronounced V-shaped joint below the proximal hydrocladium.

Hydrocladia long, internodes short, nodes marked by a small constriction, a septum passing into back of the hydrotheca and another, very short, at base of the lateral nematotheca.

Hydrothecae crowded on internode, semi-sigmoidal in shape, abcauline hydrothecal wall somewhat thickened, a short intrathecal septum passing forward into the hydrotheca. Hydrothecal margin facing obliquely upward, with two broad lateral lobes and a large median anterior spine-shaped crest.

Median nematotheca overtopping hydrothecal margin, conical in shape, abcauline wall straight or very slightly convex, tapering from base to a small round terminal orifice; a secondary orifice at junction with the hydrothecal abcauline wall. Lateral nematothecae tall, upright, of similar shape to median and at a similar angle to the internode, abcauline wall slightly convex and sinuous, adcauline wall concave, overtopping the hydrotheca, with a small round terminal orifice and a secondary orifice into the hydrotheca near the base.