Everytime that I look at a croceas "vascular system" or and/or Zooxanthellae Tubular System I am amazed.
I think of it this way.
With most other clams it's like taking a piece of wood and drilling 20 - 1/8 inch holes in it and then submerging it in water (the water being the light). It's obviously going to take less water to fill all of those holes. Now with a Crocea, it would probably be similar to taking the same sized piece of wood and drilling 400 - 1/8 inch holes in it. Much more "water" is going to be needed to fill the holes. Their inherit ability to develope Iridophores (the eyes and false eyes the intensive light requiring Zooxanthellae generate around), is astounding. They will continue to form them, and form them, and form them, and form them, then they MIGHT develope a hyaline structure - which will most of the time "dissolve" for other reasons. It might be a bad example, but it's similar to the way that some plants need MUCH more light then others.
The best way is probably to look at them though. If you look at a Maxima, Squamosa, Derasa, Gigas, whatever it is, look for the bumps or eyes all over the clam; then look at a Crocea. A really hard look needs to be taken at the mantle pretty close (with the bare eye is fine). The difference in these little bumps (between Croceas and the most of the rest of the Tridacnids) or eyes is in the hundreds or thousands most of the time. And I am talking about all of the eyes, no matter what color they are - if they are pin-sized "eyes" or ones up to the regular size of grouped symetrical ones. Croceas tend to look like they almost have an acne problem compared to other clams (more mouths to feed).
I have NEVER seen a Crocea that has been alive 6+ year in a home aquarium in my life. I have seen hundreds if not thousands of the other species though. Which is why (and I am doing a write up on this which is why the other post was pulled), based on what I have seen, Croceas should NOT be kept under T5s and IMNO out of the hobby all together.
