Halecium nanum Alder, 1859

Proximal part of stem lightly fascicled, perisarc moderately thick, irregularly branched alternately in one plane, internodes long, slender, widening distally to a transverse or slightly oblique constriction in the internode. Hydrothecal apophysis just below node.

Primary hydrothecae sessile, shallow, sometimes with up to six replications, each arising from diaphragm of the preceding one. If present, hydrophores are constricted proximally and slightly inflated above the constriction. Hydrothecal margin slightly flared; diaphragm distinct with a ring of dot-shaped desmocytes above.