The above is a picture of a Sea Anemone. Sea Anemone are found all over the world - mainly in warm coastal waters. They range in size from five inches to six feet in diameter. They have a crown of tentacles arranged around their mouth - which are poisonous:
On the tentacles are stinging cells or nematocysts. A nematocyst is a small capsule with a thread-like tube coiled inside. When a trigger bristle is disturbed, the coiled tube shoots out and imbeds in whatever triggered it. There is a minute amount of poison injected. The nematocysts are used both for defense and capturing food.
The sexes are separate. The eggs or sperm are ejected through the mouth. The fertilized egg develops into a planula, which finally settles down somewhere and grows into a single anemone. Asexually they reproduce by pulling apart into 2 halves, or, in some species, small pieces of the pedal disc break off and regenerate into a small anemone.
Which brings us to one of the more interesting things about sea anemones. Researchers at UC Davis have studied a species of sea anemonee known as Anthopleura elegantissima. Anthopleura elegantissima are organized into large colonies of genetically identical clones. Social structure is similar to insects in that their are scouts, warriors and reproductive individuals. Differentiation depends on a combination of enemy stings and the genetics of the colony. You may have noted I said "enemy stings". From the press release:
Where two colonies meet they form a distinct boundary zone. Anemones that contact an animal from another colony will fight, hitting each other with special tentacles that leave patches of stinging cells stuck to their opponent.
This is how it works:
When the tide is out, the polyps are contracted and quiet. As the tide covers the colonies, "scouts" move out into the border to look for empty space to occupy. Larger, well-armed "warriors" inflate their stinging arms and swing them around. Towards the center of the colony, poorly armed "reproductive" anemones stay out of the fray and conduct the clone's business of breeding.
When anemones from opposing colonies come in contact, they usually fight. But after about 20 or 30 minutes of battle the clones settle down to a truce until the next high tide.
It's not just polyps along the border between two clones that clash. Polyps three or four rows away from the front will reach over their comrades to engage in fights...
The lesson to take away from the study, according to the researchers, is that:
"...very complex, sophisticated, and coordinated behaviors can emerge at the level of the group, even when the group members are very simple organisms with nothing resembling a brain..."