A colonial hydroid consisting of one or many, tall, erect, feather-shaped plumes with a tapering outline above, and a distinct main stem. The plumes are up to 15 cm in length. The hydrotheca surrounding the polyps are cup shaped (230-280 µm in length). Defensive structures, termed nematotheca, lying along the mid-line of the branches are slightly upwardly curved and longer than in any other hydroid in this family (ca. 500 µm) and, hence, characteristic of this species.