Bryozoan & Ascidian

Bryozoans are colonial animals which live attached to the sea bed and although numerous they are often overlooked.

The individuals making up the colony are usually less than 1mm long, but colonies can span over one metre.  Also known as sea mats as they tend to encrust the surfaces of stones or seaweeds, however there are other colonial forms such as coral like growths, branching plant-like tufts and fleshy lobes. 

Ascidians are commonly known as sea squirts.  Despite having soft bodies they are not invertebrates but are primitive chordates, the phylum to which back-boned animals belong.

Sea squirts live attached to hard surfaces such as rocks, reefs and shipwrecks, sometimes growing together in clumps with cnidarians and sponges – they can be very colourful.   They spend their time filtering seawater, drawing in food-rich water through one siphon (inhalant) and releasing waste water through another (exhalent).  Most occur in shallow water where there is plenty of plankton, but there are a few deep-water species. 

Star Seasquirt – Botryllus spp

Individual Star Sea Squirts are only very tiny animals measuring 2 mm long and cannot live on their own. Instead they arrange themselves in star shaped colonies, on rocks or seaweed on the shore and in the shallows, in a communal gelatinous casing which can cover an area up to 15 cm across.  This casing is called a 'tunic' or 'test' which encrusts the substrate.  At the centre of each star is a shared exhalent opening through which water is expelled.  The colonies very greatly in colour and may be green, violet, brown or yellow with the individuals having a contrasting colour to the test.


Light Bulb Seasquirt - Clavelina lepadiformis

Light bulb sea squirts are conspicuous translucent animals living in colonies attached to rocky substrate and growing up to 20 mm in height. They are a delicate sublittoral species which are very sensitive to exposure by the tide.  The animals brood their eggs and young within the 'body' cavity which can be seen by the naked eye.  The animal gets its name from white lines, which are present around the opening of the seasquirt and in the body cavity as long lines extending from the top to bottom which give the seasquirt a light bulb appearance.


Ross Bryozoan - Pentapora foliacea

It is not actually a coral but rather a sea mat. Sea mats are a class of mostly marine animals found around the whole of the British Isles. They consist of many individual animals living in small box-like compartments forming part of the skeleton made from limestone, or sometimes a material similar to your nails. This skeleton forms a large complex structure which can help attract and trap food-carrying water. Each individual animal has a finely formed crown of tentacles for collecting the finely suspended food particles from the water. The Ross coral is a rust-red in colour with large colonies having a shape which resembles a human brain. This shape merely allows more water to be trapped in the complex structure allowing more food to be trapped and consumed. Ross corals are very brittle and easily damaged, especially by activities such as crab potting and divers kicking them with their fins.