Bugula neritina is an erect bryozoan that forms luxuriant tufts up to 8 cm high. The colonies are composed of dichotomous branches, which have a light spiral growth at the tip. The colonies are a vivid purplish-brown when alive, and a distinctive translucent brown when they have been preserved.
Autozooids are large and narrow towards the base. They lack spines or avicularia; all other British Bugula species have avicularia.
The species colonises a range of substrates including pier piles, ships’ hulls, buoys and similar artificial submerged structures, where it can reach a very high abundance. Small modified zooids which resemble rootlets (rhizoids) are used to attach to the colony to the substrate.
The species is recognised as a serious fouler, and can grow freely in ships’ intake pipe and condenser chambers. It settles readily on immersed test surfaces and has become invasive in New Zealand ports. The native range of the species remains uncertain. Today, B. neritina is widely distributed in warm-temperate and subtropical coastal waters. In Britain, it has been recorded from southern coasts, the east coast up to Lowestoft and on the west coasts as far as the Firth of Clyde.