Electra monostachys (Busk, 1854)

General description: 

Electra monostachys is an encrusting bryozoan species, most frequently occurring on stones or shells in estuarine environments. Colonies form irregular patches, or branched or star-shaped sheets, with several series of zooids growing rapidly in opposing directions.  The species is abundant in the lower reaches of rivers in conditions of high and fluctuating salinity, but can also occur in lagoonal, coastal or offshore environments.


Colonies grow through asexual budding of new zooids at the periphery. New zooids bud from the founding zooid (the ancestrula), primarily in lateral directions.


Electra monostachys forms irregular encrusting colonies in dendritic or star-shaped patterns, with several series of zooids grow rapidly in opposing directions.  Lobes of the same colony frequently meet and rejoin.

Zooids are flat and elongated, narrowing towards the proximal end (closest to the colony origin).The size of zooids is typically 0.44-0.5 by 0.24-0.28 mm. The non-calcified section of the zooid’s frontal surface (the frontal membrane) and the underlying space (opesia) are oval to elliptical, and may be bordered by spines. A single thin, curved and pointed spine is always present in the middle of the proximal section (closest to the colony origin) of the zooid, although it is not as developed as in E. pilosa. A thin pair of spines stands erect at the distal end of the zooid (furthest from the colony origin). Up to 4 or 5 pairs of short, curved spines may also be present around the frontal membrane, but these are frequently absent.

The calcified section of the frontal surface (the gymnocyst) is smooth and lacks pores or other features. It occupies one quarter to one third of the total frontal surface. A reduced horizontal calcareous lamina (the cryptocyst) is present beneath the frontal membrane, but it is barely visible as a rim around the proximal half of the opesia.

Irregularly shaped zooids, which lack feeding apparatus (kenozooids), may occur in the space where neighbouring colonies, or branches of the same colony, come into contact.

The operculum, a hinged flap which closes the orifice, is a simple non-calcified structure, with a thin line marginal thickening (sclerite).
The founding zooid (the ancestrula) measures 0.24 by 0.18 and bears a pair of distal spines and 2-3 proximal spines. The polypide of the ancestrula has seven to nine tentacles.


The size of zooids is between 0.44-0.5 by 0.24-0.28 mm


Electra monostachys may colonise the inner surface of Ostrea valves, in association with Conopeum seurati, Conoepeum reticulum or Aspidelectra melolontha.


The distribution of Electra monstachys is imprecisely known, but it has been recorded from estuaries and coasts of the English Channel and the North and Irish Seas. It is common on lagoonal, estuarine and coastal habitats on the Adriatic shores of Italy.


Electra monostachys most frequently colonises hard substrates, typically stones or shells and is commonly found on the inner surface of oyster shells. The species occurs in offshore, coastal or lagoonal habitats, but prefers estuarine conditions. It reaches its greatest abundance in the lower reaches of rivers, in conditions of high and fluctuating salinity.

Life cycle: 

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.

Trophic strategy: 

Like all bryozoans, Electra monostachys is a suspension feeder. It feeds on small phytoplankton using ciliated tentacles of the lophophore.


In Britain, the breeding season extends from June until November. The larvae of Electra monostachys are planktonic cyphonautes larvae which feed and grow up to 0.165 mm in height and 0.260 mm across the base. Larvae are triangular in shape at first, with a rounded basal margin, but lengthen as growth proceeds.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith