I pretty much have no clue, but I can confirm that most starfish (and echinoderms in general) reproduce sexually and have a planktonic larval stage. Starfish can regrow severed limbs, and I think some research was done in terms of how much of the middle you need to re-grow, but my recollection is that you need more than half of the middle to be viable. There was a paper in the last month or so about ago about sand dollar larvae being able to bud: http://www.columbusdispatch.com/liv...llar.ART_ART_04-01-08_B5_V29P5DQ.html?sid=101 Note, though, that the larva looks nothing like the adult animal, and is a whole lot smaller, so this wouldn't explain your starfish. Are you sure they're actually starfish and not some other sort of critter? I can't really tell from the picture. I think there are some weird mutant species of Starfish that has 6 arms, but almost all have a 5 or a multiple of 5 (like sun stars).