Aglaophenia brachiata (Lamarck, 1816)

Colonies arborescent;

Hydrorhiza composed of a tightly matted plug of thin stolons; basal stem region cylindrical, 5 mm in diameter, heavily fascicled, polysiphonic tubes of same diameter as stolons, narrow, more or less parallel; first branch 25 mm above base, branching thereafter almost in one plane in five to six orders, branches thick, polysiphonic; higher order branches usually opposite, ultimate branches monosiphonic at tips; branch internodes short, nodes represented by a minor indentation in perisarc.

Hydrocladia given off frontal tube of branch, secondary polysiphonictubes parallel, each with a row of small perforations; hydrocladia short, alternate, close, almost overlapping, arising from a prominent rounded apophysis; hydrocladial internodes short, deep, nodes weakly oblique, indistinct; two broad intranodal partial septa, one below posterior of lateral nematotheca the other below posterior intrathecal septum, both septa fading downwards to base of hydrocladium.

Hydrotheca elliptical, set at an angle of ca. 30° to internode, body divided by a strong oblique forwardly tilted septum connecting with posterior intranodal septum, becoming almost parallel with abcauline hydrothecal wall and becoming less distinct, joining median anterior cusp. Margin of hydrotheca tilted backward; margin with two median anterior cusps, one above the other, the lower slightly longer, followed by three pairs of cusps (lateral view), the first and second low and blunt, embayments between shallow, the third pair sharply pointed and projecting forward beyond lateral nematothecae; in anterior view the first two pairs of cusps pointed and a little everted, posterior pair blade-shaped, inwardly directed from behind lateral nematothecae.

Median nematotheca short, broad, terminating well below margin of hydrotheca, abcauline wall decidedly convex, free part very short, aperture circular, open down to hydrotheca; lateral nematothecae tubular, broad, with circular terminal aperture and wide connection to internode; two cauline nematothecae, one on base of apophysis, the other above on internode.

Colour: Stem and primary branches brown, remainder of colony pale honey yellow.