Aglaophenia sinuosa is easily recognizable among Australian aglaopheniid hydroids by the sinuous bends at intervals along the stem, each bend marking a reversal of the direction in which the hydrocladia face so that succeeding groups of hydrocladia alternately face frontwards and backwards.
Hydrorhizal stolons thick, reptant on substrate; stems monosiphonic, up to 70 mm long, internodes short, wide, nodes transverse to slightly oblique, sloping in different directions, a deep shoulder at node.
Hydrocladia to 10 mm long, alternate, one per cauline internode, inserted on a short apophysis. Hydrocladial internodes deep, nodes slightly oblique, distinct, a weak intranodal septum sometimes below posterior of hydrotheca.
Hydrotheca saccate, base convex, posterior wall deeply indented, a thick septum passing down into body from junction of abcauline wall with mesial nematotheca, edge of septum ragged in anterior view. Margin sloping sharply downwards to internode; margin (lateral view) with a thick rostrum overtopping median anterior tongue-shaped cusp, flanked by 2 pairs of tongue-shaped cusps and a pair of sharp, upwardly pointed cusps behind nematothecae. In anterior view, first pair of cusps outwardly directed, second pair produced inward over hydrothecal margin, third pair slightly outwardly directed; the entire margin having a fluted appearance.
Mesial nematotheca short, free end blunt, reaching level of intrathecal septum, margin widely canaliculate, curving down to junction with hydrotheca. Lateral nematothecae conical, widening from base to margin, base parallel with internode, orifice circular, level with node, excavated down to internode.
Three cauline nematothecae:i) on front of internode at base of apophysis, facing inwards, ii) between apophysis and proximal node, facing outwards, iii) one behind apophysis; all nematothecae with 2 opposite orifices.
Colour: dark brown.
Southern and eastern Australia: New South Wales, Queensland, Victoria.
Subtidal, on rocky substrates.