A sea Anemone has a simple design often little changed from the description I gave in the intoduction to cnidaria. "radially symmetrical (the body is symmetrical around a central axis).

They have a single mouth, also acting as the anus" "which is surounded by variable numbers of tentacles armed with stinging cells. This mouth opens into a single body cavity "

They usually follow the polyp version of this design i.e they have their mouth and tentacles at the top

There are however a few adaptions to this simple design.They have a modified lower end, called a pedal disc. It is muscular and is often used to attach the animal firmly to any solid object. It comes in a variety of shapes, for example it is often pointed on anemones that specialize in burying themselves in the sandy bottoms. This pedal disk enables them to be mobile; anemones in the aquarium will often move around until they find a place that they like before staying put.

For this reason care should be taken to guard pump inlets from damaging the animals. The body cavity is also modified, they have internal verticle partitions called mesenteries.These are radially symmetrical, extending from the wall of the body cavity some way towards the centre of the anemone and up to the lower surface of the oral disk. This leaves a central area like a throatThe relative size of the oral and pedal disk can vary from species to species. This results in a wide variety of shapes, with the body having to taper either in or out to accommodate their relative sizes.Most Sea anemones live in partnership with a symbiotic algae called zooxanthellaes. This means that most require good lighting to survive in the aquarium.

Sea anemone colour and shape is highly variable, as it is with most corals. This is especially true in the aquarium where both can be affected by waterflow, lighting levels and adaptions in feeding habits. A good example is the relationship the animals have with their symbiotic algae. These can either stimulate pigment production, to act like a sunblock or, in less well lit areas, just impart their own golden brown colour to the animal

It is worth noting that when stressed, all animals that use zooxanthellae can expel them in a process commonly called bleaching. This results in an apparent whitening of the anemone (or coral). At this point the loss of a valuable food source results in a slow starvation and eventual demise.

Examples pictures from our tanks