Hairy Sea-mat

Overview

The Hairy Sea-mat is a colonial bryozoan that forms thin, calcified, and often star-shaped or sheet-like patches on various marine surfaces. These colonies are composed of numerous tiny, individual animals called zooids, which collectively create a lacy or bristly appearance on their host substrate.

Distribution & habitat

This species is widely distributed across temperate seas, including the North Atlantic, the North Sea, and the Mediterranean. It is commonly found in intertidal and shallow sublittoral zones, where it attaches to hard substrates such as rocks, shells, and various macroalgae, including kelp and fucoids. While typically found in marine environments, it can also inhabit brackish waters.

Appearance

Colonies are generally silver-white and highly polymorphic, adapting their shape to the surface they colonize. On broad, flat surfaces, they form irregular sheets or star-like patterns, while on narrow stems, they may grow as cylindrical encrustations. Each oval-shaped zooid is protected by a calcified exoskeleton with a membranous window. A defining feature is the presence of 4 to 12 spines surrounding this window; the central, proximal spine is often significantly longer than the others, giving the entire colony a distinctively "hairy" look.

Biology & behavior

As filter feeders, these organisms extend tentacles to capture suspended particles from the water column. The colonies grow through asexual budding of new zooids, allowing them to expand rapidly across surfaces. While they have few natural predators, they are occasionally grazed upon by nudibranchs, sea urchins, and sea spiders.