The aptly named and very distinctive bottle brush hydroid - Thuiaria thuja - is unlikely to be confused with any other hydroid. It is a cold water species and confined to more northern coasts of the UK – as far down as Northumberland in the east and the northern Hebrides in the west. They are found attached to hard surfaces and when young they have a feather-like appearance, only developing their bottle brush shape once they reach a size of around 2cms. They can grow to a maximum of 25cms.

Location: St. Abbs Marine Reserve