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Cultivated Reef

Sea Star or Urchin?


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Even after the tank has been established for over a year, I am still finding new hitchhikers! Just spotted this critter this morning. At first, I thought it was a blunt-armed sea star, but they are only supposed to have 5 arms, and this pretty clearly has six. Maybe it is a kind of urchin? The colors are difficult to see in the picture, but it is white with green mottling/spots. It is puffy, not flat. It has a textured body that could be bumps or itsy-bitsy spines. My LR came from the Gulf, but I cannot say for sure where all the coral came from. It moves ever-so-slowly, and when it does, the arms sort of draw together and the middle part looks fatter. It has been on the move the last few hours and made it about 1 inch!




Note: according to Wikipedia, "Most starfish typically have five rays or arms, which radiate from a central disc. However, several species frequently have six or more arms. Several asteroid groups, such as the Solasteridae, have 10 to 15 arms, whereas some species, such as the Antarctic Labidiaster annulatus can have up to 50. It is not unusual for species that typically have five rays to exceptionally possess six or more rays due to developmental abnormalities.[4]"

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Hmm -- just spotted three more. There not quite as irregularly shaped as the asterina anomalas shown in many pictures. All four are about the same size, too, with six symmetrical arms which seems less likely given asexual reproduction by tearing off one half of the body and growing a new one (unless all of these are adults). Some sites state these are bad, probable coral eaters, depending on size. Thus far, the four I see are on back wall and rock or dead coral (coral that has been dead). I would hazard that my generous feeding regimen has once again changed the life in the tank.

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