Translucent grey or white, marbled, speckled and streaked with white, orange, red and brown in various proportions (D. frondosus creeping). Specimens from deep coastal water (below 25 m) are usually paler than those from shallower habitats. There are also differences associated with age. Juveniles up to a length of 4 mm are pale (D. frondosus-juvenile), then from 4 to 30 mm the developing patterns may become vivid, forming stripes along the sides and back, with contrasting bands of colour on the cerata. In specimens over 30 mm, the pattern once again becomes drab.
Has not yet been assessed for the IUCN Red List.
Boreo-Arctic. In North Atlantic as far south as France (on European coast), and New Jersey (in North America). In North Pacific as far south as Los Angeles, California.
Intertidal, bathyal, infralittoral and circalittoral of the Gulf and estuary.
Dendronotus frondosus is hermaphroditic. The larval stage of the development is asymmetrical, although the adults show bilateral symmetry
Maximum size of 10 to 60 mm in length
Juvenile animals feed on calyptoblastic hydroids such as Sertularia cupressina & Dynamena pumila while adults feed on the gymnoblastic hydroids of the genus Tubularia.
Change in diet from small colonial calyptoblastic hydroids to larger gymnoblastic tubularians.