Electra pilosa is an encrusting bryozoan species, common to the British intertidal zone and subtidal waters, down to approximately 50 m. The colonies form white circular, lobe- or star-shaped patches, several centimetres in diameter, often with a “hairy” appearance. E. pilosa is able to colonise shells, stones, the talli of red algae and the fronds of fucoid and kelp species. The shape and size of the colony is dependent on the substrata on which it is growing.
The species is widely distributed across the North Sea, the Wadden Sea, the north Atlantic and some Arctic and sub-Arctic regions (the White Sea and the Barents Sea). It is has been recorded from many British and European coasts, as well as from the Gulf on Maine. The species has also been recorded from New Zealand and Australia, where it is considered an introduced species.
Colonies grow through asexual budding of new zooids at the periphery.
Several bryozoan form similar encrusting white colonies. In particular M.membranacea bears a superficial resemblance to Electra pilosa, having a similar colony form and colour and occupying similar habitats. M. membranacea can be distinguished by its rectangular zooids, compared to the rounded zooids of E.pilosa. Zooids of E.pilosa also have a characteristic large central spine.
Electra pilosa forms white encrusting colonies, which often have a hairy appearance. The colony form varies according to substrate: small, irregular patches are typical on stones and shells, while cylindrical encrustations form around the branching fronds of small red algae (e.g. Gigartina and Mastocarpus stellatus). Broad or star-shaped sheets, where several series of zooids grow rapidly in opposing directions, may form on the smooth, homogenous fronds of the kelp, Laminaria, and the red algae, Rhodymenia. Narrow tufts, independent of the substrate, may form when colonies encrusting branched or cylindrical substrata grow rapidly away from the substrate. This growth form was previously referred to as a separate species (Electra verticillata) and is thought to arise when a colony encrusting a substratum of limited extend e.g. an erect hydroid, rapidly utilizes the entire available surface.
Zooids are oval or rounded-rectangles which narrow towards the proximal end (closest to the colony origin). In the encrusting forms, zooids are arranged in a parallel rows, with adjacent zooids slight offset from each other such that a regular series of quincunxes (five zooids in a square, with one zooid at each corner and one in the middle) are apparent. In the extended linear growth form (previously Electra verticillata), the zooids comprising adjacent rows lie side by side without alternation.
The size of zooids varies greatly, but is frequently between 0.5-0.6 by 0.25-0.35 mm. The calcified section of the frontal surface (the gymnocyst) occupies one half to one third of the total frontal surface. The calcification is light and the polypide (which has 11-15 tentacles) is typically visible through the frontal surface. The non-calcified section of the frontal surface (the frontal membrane) and the underlying space (opesia) are oval in shape with a distinct rim. Between 4 and 12 (often 9) spines surround the frontal membrane and opesia. A large spine, light brown in colour, is located in the middle of the zooid, towards the proximal end and is always present. This spine is characteristic of the species, but it is frequently broken off and therefore not visible. This spine can become enlarged, reaching 2-3 times the length of the zooid, and is responsible for the “hairy” appearance of E. pilosa colonies.
The size of zooids varies greatly, but is frequently between 0.5-0.6 by 0.25-0.35 mm
Electra pilosa is able colonise hydroids, the fronds of fucoid species (Fucus serratus), kelp species (Laminaria), red algae species (e.g. Gigartina, Mastocarpus stellatus and Rhodymenia) and other bryozoan species such as Flustra foliacea. In Britain, except in the south west, E. pilosa is the main food source of the dorid nudibranch Adalaria prxima. The nudibranch larvae settle in early summer and only metamorphose when they are in contact with E. pilosa. Small pycnogonids such as Achelia longipes may also be found associated with E. pilosa colonies.
Electra pilosa was first described by Linnaeus from the NE Atlantic, and it has subsequently been recorded from the NW Atlantic, the North Sea and the Wadden Sea. The species is known to occur in some Arctic and sub-Arctic regions (the White Sea and the Barents Sea) and extends south to the Mediterranean. The species has been recorded from New Zealand and Australia, where it is considered an introduced species.
Electra pilosa is common on sheltered rocky shores down to depths of around 50 m. E. pilosa colonises almost any substratum including shells, the talli of red algae, various hydroid species, the fronds of fucoid species (Fucus serratus) and kelp species (Laminaria). Of the three British species of Electra, E.pilosa is the only species which doesn’t appear to prefer estuarine conditions, but nonetheless has been recorded from brackish environments e.g. the Tamar Estuary and the Baltic Sea.
The founding zooid (ancestrula) develops into a young colony, and later into an adult colony through asexual budding. Sexually produced embryos develop into larvae which are released into the plankton. Larvae settle after liberation and metamorphose into an ancestrula.
Like all bryozoans, Electra pilosa is a suspension feeder. It feeds on small phytoplankton using ciliated tentacles of the lophophore.
The founding zooid (ancestrula) develops into a young colony, and later into an adult colony through asexual budding. Sexually produced embryos develop into larvae which are released into the plankton. Larvae settle after liberation and metamorphose into an ancestrula.