In amongst the tentacles of this sea anemone is a Spine-cheeked Anemone fish. (similar to Nemo) These little fish with big attitude live in a commensal relationship with the anemone. The anenome has stinging cells in its tentacles which fire when touched - to disable prey and for protection, however the anemone fish is not bothered by this like other creatures are and thus can use it as a safe retreat (their home). Family groups each have their own anemone and even though they are only an inch or two long they do not hesitate in swimming at a diver, or trying to bite a finger (they can't) to defend themselves and their anemone. If they were bigger they would be scary. Anemones are related to corals in that they are all the the taxa of Cnidarians (along with seajellies).
Sea Anemones can retract their tentacles as this one has. The family of fish hovering over the top are Pink Anemonefish .
Although sea-squirts (ascidians) are very simple animals consisting of sack like body with two openings - one inlet for taking in water/food and one outlet to allow the water (filtered of its plankton) out, they are actually very interesting. In the beginning of their life they are in the form of a tiny tadpole like larva that swims around from anything from 10 minutes to 8-10 hours( depending on the species) before they settle on the substrate. At this stage they have a very basic spinal chord. They are the most primitive creatures with what has become a backbone with spinal cord enclosed in it, like we have...We evolved from something like this. They belong to the phylum Chordata like us. Some live as solitary creatures like this one which is a Polycarpa aurata or they can be colonial. They remain anchored to the place where they settle.
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