Tessaradoma boreale (Busk, 1860)


Tessaradoma boreale is an erect bryozoan that consists of rigid cylindrical branches, which divide dichotomously. The unjointed colonies are spreading, reaching up to 50 mm high. The branches are always slender, rarely exceeding a thickness of 1 mm at the base, and narrowing towards the growing tip. Colonies attach to the substrate via an encrusting base. As the colony grows, the basal regions are strengthened by continuous thickening of the frontal walls of the lowest autozooids. The original outlines of the autozooids are lost as the dividing walls are broken down.

Autozooids are elongate, oval and arranged back-to back in alternative pairs. They are 0.7-0.8 by 0.3 mm, broadening in the older parts of the colony.


Tessaradoma boreale is characteristic of deep fjords, the continental slope, and the outer shelf, with most British records coming from Shetland. It is widespread throughout the North and South Atlantic, but apparently restricted to temperatures of 2-13 degrees Celsius.


The species is able to colonise stones, shells, serpulid tubes, other erect bryozoan species, hydroids and the cold water coral Lophelia. It ranges from 70 m in the Arctic to 3700 m near the equator.

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