Here's a naive question: Can physical distortions be caused by decompression when deep-water critters move to shallow water?
Yes. Fishes containing swim bladders will. They need to be yanked into shallow water rather quickly, however. The bladder tends to expand forward up into the throat.
Under natural conditions however, animals migrating from deep to shallow water don't normally look much/any different. That's because they don't have air spaces in their bodies. Sometimes you see colour pattern changes 'cuz they're *pissed off* about the shallow water being warmer, but that's about it.
Many species of starfish have incredibly flexible internal storage capacity in the central disk and upper arms. These spaces can be filled with ingested food items, and even occasionally, stored eggs and sperm.
In the case of your
Tethyaster-looking starfish, I would wager that the animal has ingested a huge clump of seaweed, garbage, or even an animal carcass, and stuffed it up inside it's body to digest. I occasionally see deepwater starfish (usually big specimens like yours) with this appearance. One of these was in fact a
Tethyaster, but in that case the central disk swelled up like a bowling ball (really messed up looking!) and the arms were left nice and flat. Now that I think back on that specimen, I do recall that the arms did look like they were capable of significant expansion.
So maybe that's whats going on. Or maybe it's just deformed.
