Hydrozoa note details
Colonies erect, arising from a stolonal hydrorhiza; hydrocauli unbranched, divided into internodes, giving rise to hydrocladia from alternate or mostly alternate apophyses, cauline hydrothecae absent; hydrocladia dichotomously or irregularly branched, or unbranched, divided into internodes, often with terminal hydrothecae; hydrothecae uniseriate, sessile, small, cup-shaped, relatively shallow, free of hydrothecial internode or not completely adnate; radially symmetrical; margin entire; operculum absent. Nematophores and nematothecae absent. Gonophores presumably fixed sporosacs; gonothecae solitary, conical, without nematothecae, arising from apophyses of hydrocaulus; phylactocarps absent.
Choong H., Calder D., Chapman J., Miller J., Geller J., Carlton J. (2018). Hydroids (Cnidaria: Hydrozoa: Leptothecata and Limnomedusae) on 2011 Japanese tsunami marine debris landing in North America and Hawai‘i, with revisory notes on Hydrodendron Hincks, 1874 and a diagnosis of Plumaleciidae, new family. Aquatic Invasions. 13(1): 43-70.