Dive Dry with Dr. Bill

082: Cerianthid Anemones

As children at the dinner table, our parents often told us not to eat with our hands. I know mine did back in the days when families actually sat down together for the main meal. For many marine organisms, this is the only way they can eat. Knives and forks are rarely found underwater (except during the Avalon Harbor Cleanup). One such critter is the beautiful cerianthid anemone, a relative of the corals and jellyfish.

Cerianthid anemones live on the soft bottom in papery tubes, and are fairly common in the sandy areas just beyond the kelp forests and rocky reefs in the Dive Park. The tubes are secreted by the anemone using special groups of cells. Our tube-dwelling anemones are known from Alaska down to Baja California in waters down to 70 feet or more along protected coasts such as Catalina's leeward side. They may reach 12" high when they emerge from the safety of their homes.

In the open they extend their many arms, known as tentacles, into the surrounding water to capture food drifting by. Like their relatives, these tentacles contain stinging cells known as nematocysts which capture the food. When a tentacle captures food, it is brought towards the central "mouth" opening. Here the long feeding tentacle is wiped along a series of shorter, bristle-like tentacles which remove the food and transfer it into the mouth for digestion.

Although they are called anemones, the cerianthids have some important differences from anemones like those commonly seen in tide pools here. Other anemones take their food into the "mouth" opening, digest it in a simple stomach, then expel the undigested material back out through the mouth since they have no anus. If feeding with their hands wasn't enough, these anemones poop through the only opening they have. Cerianthids on the other hand have a small anal pore at the other end, although I'm not certain if they use it or their mouth. Scientists actually know relatively little about these animals... except that they have an anus!

The animal may be creamy white, dark brown or black, or orange in color. The orange ones look like beautiful flowers underwater. However, when disturbed the anemone and all its tentacles can be quickly withdrawn into the tube for protection. When I encounter one of the orange individuals, I usually use my underwater lights to accentuate its color since red and orange sunlight does not penetrate to the depths I often see them at. Occasionally when I turn on the light, they almost instantaneously retreat into the tube.

In some areas of their range these anemones are preyed upon by a nudibranch (shell-less snail). The nudibranch feeds on the tentacles and usually does not kill the anemone itself. Kind of like carving a piece of beef off the cow without killing it... talk about "mad cows." Sometimes when the anemones withdraw on attack, the nudibranch is pulled into the tube as well where it continues munching away on the tentacles. The stinging cells do not bother these predators, and the tube doesn't always provide protection against them! Despite these attacks, cerianthids may live to be 10 years old... hmmm, no wonder they act like children at the dinner table!

© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Upper: two differently colored cerianthids with tentacles extended to feed; Lower: ceranthid brushing food
off a feeding tentacles and transferring it to the oral region; cerianthid withdrawn into tube for protection

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia