Sea Anemones (pronounced: a-NEM-o-nee) belonging to the phylum Cnidaria (pronounced: NY-deeria) are really interesting tide-pool creatures. When the tide is in and they are under water, sea anemones look rather like beautiful flowers (see photo below).
As the tide recedes, sea anemones force water out of their body cavities, retract their tentacles, and fold inward to survive the low tide, transforming themselves into very unattractive, globular or pendulous masses (see photo below). This photo was taken at an extremely low tide.
Who would ever guess that the seemingly sessile globs of Giant Green Anemones (Anthopleura xanthogrammica) covering the rock in the photo above are carnivorous predators? When submerged, they are each capable of capturing and digesting crabs, mussels, or any other animal unlucky enough to be within reach of one of its stinging tentacles (retracted during a low tide in this photo).
It isn't until a person witnesses a sea anemone capturing live prey that he/she truly appreciates the predatory skills of this animal. Last summer we were at Myers Creek Beach, just south of Gold Beach, when we spotted a very unlucky Ochre Star that had become dislodged from the rocks above and became dinner for this Giant Green Anemone.
When the anemone is finished digesting the protein part of this sea star, the unused parts will be ejected through its mouth. Sometimes, the anemone will extrude its stomach through its mouth in its efforts to rid itself of undigestable parts of its prey (see below..the onion skin bulb is the stomach).
In order to better understand how an anemone captures prey, avoids predators, and survives in the harsh environment of the intertidal, a simple drawing of an anemone's body (see below) can be used as a reference.
Whenever a sea anemone is digesting, disturbed, or left high and dry due to a low tide, it will force water out of its column, retract its tentacles into its body cavity and fold inward. A sea anemone's body is essentially a hollow column (or tube) with a mouth at the top, surounded by sticky, stinging tentacles. The tentacles, which look a little like the petals on a flower, will sting any prey that inadvertently touches them (human finger's will only feel a gentle tugging...not harmful or lethal).
The stickiness of the tentacles, combined with the anesthesizing effect of the sting, imprisons the prey. The sea anemone wraps all its tentacles around the captured victim to pull it into the anemone's mouth. The muscles lining the the anemone's hollow body cavity force the prey further down the gut to the digestive organs located at the bottom.
Sea Anemones have the following characteristics in common:
- Tentacles fortified with stinging cells, called nematoycysts (pronounced nem-o-toe-sist)
- Radial symmetry (circular shaped, like bicycle spokes)
- A primitive nervous system
- A muscular system for forcing food down body cavity, for scrunching down tight in self defense, and for "walking" away from predators or a hostile changing environment (i.e., encroaching sand)
- A sensory system that is a smell-taste-sense chemical compound (not a specific smell organ, like a nose)
- Bascially stationery, but can move
- Relatively few predators, namely Nudibranch and Leather Stars (Dermasterias imbricata)