A colonial hydroid that grows up to 15 cm or more. It is straggly in appearance with alternate branches, widely spaced along the stem. The hydrothecae, a supporting, nonliving, protein-chitinous envelope surrounding the stem, is large, up to 1.6 mm long, tubular and variously outward curving. It is easily mistaken for a sparsely branched form of Abietinaria abietina
but is distinguished by opposite hydrothecae.