Antennella secundaria (Gmelin, 1791)

Hydrocladia up to 8 mm high, arising from a tubular hydrorhiza reptant on substrate; single nematothecae arising at intervals from hydrorhiza. Proximal part of hydrocladium with one to three athecate internodes, nodes transverse, each internode bearing one o r two nematothecae, distalmost node strongly oblique. Hydrocladial internodes thereafter of similar length, alternately thecate and athecate, proximal node of thecate internode strongly oblique, passing beneath hydrotheca, distal node transverse below hydrothecal margin.

Hydrotheca occupying almost entire internode, facing forward at an angle of c. 60° to hydrocladial axis, deep cup-shaped , walls almost parallel but abcauline wall sometimes faintly sinuate, free adcauline wall straight to slightly concave, adnate part convex, curving back to small hydropore at base of abcauline wall, perisarc thickened a round base; margin circular, slightly sinuous.

Nematothecae bithalamic, small, two on athecate internode, basal chamber stout, cup small, foreshortened on adcauline side; mesial inferior stout, adcauline side of cup foreshortened, just reaching base of hydrotheca, lateral nematotheca borne on a long, slender pedicel where adcauline wall of hydrotheca becomes free, cup broad and shallow, excavated on adcauline side, not quite reaching hydrothecal margin; a small mesial superior nematotheca inserted beneath hydrotheca, flattened, facing forward , borne on a short, thick pedicel beside mesial inferior nematotheca; two large nematothecae at base of gonotheca; basal chamber of these long, cup wide, shallow, excavated on side facing gonotheca.

Orifice of gonotheca distal, subcircular, closed by a thin operculum. Male gonotheca considerably smaller than female, borne behind hydrotheca in same position as female, ovoid to kidney-shaped, flattened, apically blunt to rounded; no obvious orifice; a single small nematotheca at base, cup deeper and narrower than those on female; excavated on adcauline side.

Colour: Greenish-yellow.