Bryozoans and hydroids
Just as you think you are getting the hang of this rock pooling thing you pick up something and it doesn’t look right. On the strand-line a leaf-like object, clearly a dried up seaweed catches your eye. It is rough, grey and the size of your hand. You look a little closer and it seems to be made of individual cell-like structures. Welcome to the world of colonial polyp type organisms that seem to defy identification.
A bryozoan is an animal that lives in a colony, it starts as a single unit, a zooid. This consists of a calcium-based structure like a little box and inside lives a tentacled coral like lophophore. From this single unit, others bud forming a structure that is species specific. In primitive forms, all the units are feeding capable (autozoid), they are self-sufficient. In more complex types additional cells or units (heterozoids) are created that cannot feed themselves, some of these resemble bird beaks. The feeding tentacles are covered in fine hairs (cilia) these beat and create a current drawing in food particles. Hydroids lack these hairs but they resemble bryozoans in many other ways. Interestingly they seem to have the ability to break down parts of their bodies and reform them.
Like anemonies, they have differing breeding mechanisms, some brood internally and release a free-swimming form that settles after a few days and starts a new colony. Others broadcast sperm and eggs and these then produce a swimming version. Some species are specific to the substrate they settle on and it is thought they can chemically locate their preferred plant. Once they settle they ‘snuffle’ they move around to ensure all is correct and then they secrete a glue and the colony starts.
The seaweed we have found is actually Hornwrack, Flustra foliacea, this is a large colony of bryozoans and easy to identify. Many though are extremely difficult, not only do they have multiple growth forms many are small and you assume they are just some sort of detritus fur or muck on a rock. Sea mats cover kelp fronds like a lace network, Bugula look like little trees, some are flat on rocks like a paint form of seaweed but textured. This is a fascinating group of organisms but they require a good hand lens or microscope to full appreciate let alone identify.
Look on seaweeds for cell-like structure, on rocks for flat clusters of cells sometimes covered in a gel, on kelp and wracks for zigzag or feather-like structures. Unfortunately, the living organism only emerges in water so if you can take a picture or video submersed. Please avoid bringing these treasure home unless they are on the strandline, they may look lifeless but they are simply waiting for the water to return.
A bryozoan is an animal that lives in a colony, it starts as a single unit, a zooid. This consists of a calcium-based structure like a little box and inside lives a tentacled coral like lophophore. From this single unit, others bud forming a structure that is species specific. In primitive forms, all the units are feeding capable (autozoid), they are self-sufficient. In more complex types additional cells or units (heterozoids) are created that cannot feed themselves, some of these resemble bird beaks. The feeding tentacles are covered in fine hairs (cilia) these beat and create a current drawing in food particles. Hydroids lack these hairs but they resemble bryozoans in many other ways. Interestingly they seem to have the ability to break down parts of their bodies and reform them.
Like anemonies, they have differing breeding mechanisms, some brood internally and release a free-swimming form that settles after a few days and starts a new colony. Others broadcast sperm and eggs and these then produce a swimming version. Some species are specific to the substrate they settle on and it is thought they can chemically locate their preferred plant. Once they settle they ‘snuffle’ they move around to ensure all is correct and then they secrete a glue and the colony starts.
The seaweed we have found is actually Hornwrack, Flustra foliacea, this is a large colony of bryozoans and easy to identify. Many though are extremely difficult, not only do they have multiple growth forms many are small and you assume they are just some sort of detritus fur or muck on a rock. Sea mats cover kelp fronds like a lace network, Bugula look like little trees, some are flat on rocks like a paint form of seaweed but textured. This is a fascinating group of organisms but they require a good hand lens or microscope to full appreciate let alone identify.
Look on seaweeds for cell-like structure, on rocks for flat clusters of cells sometimes covered in a gel, on kelp and wracks for zigzag or feather-like structures. Unfortunately, the living organism only emerges in water so if you can take a picture or video submersed. Please avoid bringing these treasure home unless they are on the strandline, they may look lifeless but they are simply waiting for the water to return.