Alcyonidioides mytili

This species is currently accepted as Alcyonidioides mytili

When colonies are in the early stages of growth they are unilaminar and iridescent. As they develop they start to produce kenozooids in amongst the autozooids and the colonies thicken into multiple layers. These layers give the colony a grey, opaque appearance. As the colonies develop, the autozooids are arranged into such a way that excurrent chimneys can be seen, giving the colony a knobbly appearance. These chimneys are important in the process of sperm dispersal.

This species is most likely under recorded. It has been observed as far north as Sutherland (North Scotland) and Loch Maddy (Hebrides), west around Galway on cultured mussels, south to Pembrokeshire (Milford Haven) and on the eastern side of the UK at the island of Sylt (North Germany).

The colonies grow on Mytilus edulis valves, but can also be found on the slipper limpet Crepidula fornicata and Ostrea edulis shells, stones and occasionally on the stipes of Laminaria hyperborea from LWST into the shallow sublittoral

A. mytili could get confused with A. gelatinosum but colour, microhabitat and reproductive biology are different.

This species is planktotrophic, producing large numbers of microlecithal eggs. It has been observed to have a intertentacular organ.