I'm glad I saw this post. I corresponded with Rob Toonen about these stars very recently:
"I had a question for you about the starfish in the lobby tank. There are two purple stars in there that look superficially like Linckias, but with 6 arms. I know you told me the species name once, but it escapes me. Anyhow, I've found three of their arms in the refugium of the tank, and they've been alive for at least three months now. They don't appear to be bitten off or anything--both ends appear to be healed. Each "bud", for lack of a better term, is about two inches long. The tube feet move and the arms are occasionally in different areas on the rocks. They don't seem to have any part of the central disc or any mouth at all. OK, so everything I've read has told me this is not possible; these arms should have died from lack of food a long time ago, right? Is it possible that they're actually receiving nutrition somehow, and this is some weird form of reproduction?
Thanks, Matt"
"Those purple stars are usually either Tamaria stria from the Sea of Cortez or Leiaster teres from the IndoPacific - I don't know where they came from, so I can only hazard a guess at Tamaria from what I remember... Tamaria stays smaller (about 5" maximum diameter) and has more than 5 arms, whereas Leiaster has almost always got 5 arms and can get more than a foot in diameter.... Regardless of which one you have, both species are predatory on small sessile invertebrates (there have been no studies on these particular species, but all members of these two genera feed on clams, snails, sponges, tunicates and small cnidarians). To the best of my knowledge, there has also been no studies of the reproductive behavior of either species, but what you describe is very common for some species of Linckia, and could well be a form of asexual reproduction. Asterinid sea stars can go an amazingly long time without food, and can digest their inner tissues to support themselves during periods of starvation or regeneration. It is quite possible that they may be able to completely regenerate the body from a simple limb bud such as you describe, and that is actually the primary mode of reproduction for species like Linckia multifora. You can probably find some cool pics if you search for images of this species in Google..
That's great to hear - say Hi to everyone at MARS for me!
Rob"
FWIW, I believe Rob means *very* small sessile inverts, as we have have lots of sponges, snails, and small cnidarian polyps in this tank, with 2 of these stars. They have been there for over a year.