Anemones

Critter Spotlight: Anemonia manjano

Photo Credit: Bob Goemans

Photo Credit: Bob Goemans

Anemones, in the Phylum Cnidaria, Class Anthozoa, Subclass Hexacorallia and Order Actiniaria are basically simple, primitive animals. They range in size from .5 inch to over 4 feet in diameter. Their tube shaped body is usually topped with a ring of tentacles, which selectively feed on planktonic organisms or small fishes. A ring of tentacles surround an area known as the oral disc, which contains an opening in the center commonly called the mouth. Food is taken into this opening and waste matter or undigested food is expelled through the same opening. The body column sometimes referred to as a pedal column, serves as a means for locomotion or as a holdfast.

Should environmental conditions not be suitable, anemones can easily move to where light, water movement and feeding conditions are more favorable. A moving anemone is a sign it's unhappy with its environment! Anemones may reproduce sexually or asexually by splitting and fragmentation. With some anemones, asexual reproduction results in the production of clones. Clones of the same specimen can intermingle without any harm to each other. Yet clones of a different individual, even though the same species will do battle with each other. They have been known to live in captivity for almost eighty years.

All anemones are considered carnivorous even though some utilize intense light to trigger symbiotic algae living in their flesh, which in turn produce a portion of their nutritional requirements. Using small nematocysts or stinging cells, which cover the tentacles and which are capable of firing a tiny dart connected with a thin filament into its prey, the anemone is very capable of capturing planktonic organisms and small fish. Anemones have few enemies, with other anemones, nudibranchs, sea stars and some fishes considered their main predators.

Anemones have specialized defensive mechanisms that can deter potential predators, e.g., specialized nematocyst at the base of the tentacle; inflating defense tentacles called 'acrorhagi' located just below the oral disc; reducing body size; and, exuding quantities of nematocyst-laden mucous called 'acontia.'

Even though most anemones are considered carnivorous, some that interest aquarists require bright light to trigger their symbiotic algae. If conditions are not suitable, they will move to where conditions will suit them. Therefore, in a mixed anemone and coral environment it's recommended the anemone be placed in the aquarium prior to adding corals so as to allow it to find its own favorite spot. That way, the anemone passing near or over it will not damage stationary corals.

I’ll divide this subject matter into three groups, those more properly called ‘Sea Anemones’ containing many of the preferred species for aquariums, those that are troublesome in aquaria, which I’ll call ‘Pest Anemones’ and finally those that are called ‘Tube Anemones' that burrow into sand and mud.

• Pest Anemones
• Sea Anemones
• Tube Anemones