[reefjitsu]

It is absolutely not a tube anemone. It does not have the characterisitcs of tube anemones. The tentacles are the first clue. From the link I posted earlier:

So why are the cerianthids (the scientific name for tube anemones) not anemones? Aside from some internal structural differences that no one here probably cares about, there are a couple major differences between tube anemones and true anemones that are easy to see. First, they are the only "anemone-like" animal with two distinct whorls of tentacles on the oral disc - they have a batch of short "labial" tentacles which surround the mouth and then a ring of very long tentacles which encompass the outer edge of the oral disk. These long tentacles are used primarily in prey capture and defense, while the shorter labial tentacles are used primarily for prey manipulation and ingestion.

Just based on the tentacles alone, you can rule this out as a tube anemone. The specimen in question here is very obviously some type of true anemone.

This specimen is also attatched to a rock, something a tube anemone cannot do.

A second key difference between the cerianthids and true anemones is that cerianthids lack the pedal disk and all associated musculature as well as lacking any sphincter muscles - this may sound minor to you, but it means that unlike true anemones, they cannot attach their base to the substrate on which they live. Anyone who has kept a true anemone knows that a happy and healthy animal will be strongly attached to something in the aquarium at all times. Rather than a pedal disk (which true anemones use to hold onto the substrate), cerianthids end in a blunt point (sometimes called the foot) in which a small hole (which allows water to escape the inflated animal during retraction into the tube).

An easy test will be how this thing retracts. A true anemone retracts into a ball or used-chewing gum like glob. A tube anemone will dissappear into it's tube and cannot retract it's tentacles.

More importantly, however, although cerianthids can withdraw into their tube, unlike true anemones they cannot contract the oral disk or withdraw their tentacles (Brusca & Brucsa 2002). That is a pretty major difference. If you've ever seen a true anemone feed, you've seen it contract the oral disk to bring it's tentacles closer to the mouth, and when disturbed the tentacles of true anemones are retracted, the oral disk is contracted and a sphincter muscle closes the top of the animal into a ball to protect itself. Cerianthids are unable to do this, and can only retract into their tube to try to protect themselves

One last note, for the term rock anemone. Rock anemone is a common name for many (probably hundreds) of species of anemone. Don't read to much into this one not looking like other "rock anemones" you may see pictures of .