Halecium corpulatum  

Hydrorhiza comprising tangled stolons becoming fascicular tubes of erect stem.

Stems fascicled, thick, arborescent, almost planar, branching irregular from opposite to alternate, polysiphonic tubes reaching to base of ultimate branches.

Hydrophores arising from just below a hydrotheca, usually one but sometimes two opposite, one to six successive secondary hydrophores arising linearly from diaphragm of preceding hydrotheca. Hydrophores moderately long, cylindrical, increasing slightly in diameter to below hydrotheca, one to three proximal abcauline partial septa fading out on adcauline wall. One or two thickenings of perisarc at the base of a hydrotheca above junction with hydrophore.

Hydrotheca shallow dish–shaped, adcauline wall of primary hydrotheca closely adpressed to primary hydrophore, succeeding hydrothecae expanding smoothly from a transverse diaphragm to margin, a row of desmocytes just above diaphragm, sometimes a concave pseudo–diaphragm below. Margin everted and strongly outrolled, not replicated, ratio of depth of hydrotheca to diameter of margin 1:4–1:5.

Hydranth (preserved material) with a long conical or cylindrical peduncle with about 20 moderately long tentacles.

Gonotheca inserted on a very short pedicel within a hydrotheca, lenticular, wall smooth, perisarc thin, apex slightly pointed, no evidence of aperture.