Frank O
Contributor
What's going on with this sea star (shot last week in about 60 ft of water off Kona, Hawaii)? Is this a regeneration thing?
Long-armed sea star
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What's going on with this sea star (shot last week in about 60 ft of water off Kona, Hawaii)? Is this a regeneration thing?
I am assuming that it is a Linckia-type thing, and that absurdly long arm was at one point the "comet's tail" during a body fragmentation event.
Which from the animal's size, appears to have been a long time ago.
Which from the animal's size, appears to have been a long time ago.
archman:I am assuming that it is a Linckia-type thing, and that absurdly long arm was at one point the "comet's tail" during a body fragmentation event.
Which from the animal's size, appears to have been a long time ago.
What is the actual length of these stars? I'd hate to tangle with it.
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Frank O
Contributor
Well, I have to confess that the dive is now a couple of weeks ago, and I have to rely on my creaky memory and what's shown in the photo. I'll take a wild guess and say that the star's main body was about six inches across between tips of nearly-opposing normal-sized arms. So the extra-long arm was somewhere in the realm of maybe 10 inches long?
ScubaGir1
Registered
From my marine biology class, it happens when the ray (or sea star arm) has been severed off and it regenerates its ENTIRE body. Hence why one arm is so long, and the rest of it is so small (its still in growth mode). Each ray has an extension of all the organs and tissues a sea star has.
Yes, we refer to that as a "fragmentation" form of asexual reproduction. It's more common in invertebrates displaying radial body symmetry, and best known to the lay public for starfishes.
The name "comet star" is often used for ophidiasterids like Linckia, in reference to their *arm fragmentation* mode of reproduction. One (or more) arms is deliberately autotomized, and that arm regenerates a new central disk basally. That tiny new disk is what we call the "head of the comet", and the old arm is the "tail of the comet".
Most starfishes cannot regenerate whole bodies from just an arm. Normally at least one quarter of the central disk is required. Linckia's are rather odd in this behaviour of cloning new animals from arms, and represent more of an exception rather than a general rule. Arms on members of this genus tend to be pinched in at the base, which likely facilitates arm autotomy. Conversely, imaging something like a Bahamian Cushion Star trying to reproduce this way makes me wince.:11:
The name "comet star" is often used for ophidiasterids like Linckia, in reference to their *arm fragmentation* mode of reproduction. One (or more) arms is deliberately autotomized, and that arm regenerates a new central disk basally. That tiny new disk is what we call the "head of the comet", and the old arm is the "tail of the comet".
Most starfishes cannot regenerate whole bodies from just an arm. Normally at least one quarter of the central disk is required. Linckia's are rather odd in this behaviour of cloning new animals from arms, and represent more of an exception rather than a general rule. Arms on members of this genus tend to be pinched in at the base, which likely facilitates arm autotomy. Conversely, imaging something like a Bahamian Cushion Star trying to reproduce this way makes me wince.:11:
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