EH FYI......... crocea are the most difficult clams species to keep... Firstly they are rock boring clams, thus during collection, their byssal is always injured by accidental thus when the croceas arrive, they may look fine but after a while the crocea will die......Anyway byssal damage do not cause the clam to die immediately but it is a;ways due to infection that cause the clam death..... Therefore if you really want to have crocea, but those that come attach with a small piece of rock........ Next corcea are tough to keep because they love to exhibit their mantle so much, FYI crocea mantle are one of the widest when open thus they are very prone to being attack by predators or being damage by human. And finally, crocea are shallow water clams thus the light for them must be very strong(for me, i provide my clam with 400watt of light)... With so, all this factor make corcea very tought to keep........
Fpr beginner, if you have a large tank, go for derasa or squamosa, they are by far one of the toughest clams...... Being tolerant of low light intensity(some ppl keep them under Pl).... But the bad point is sqaumosa and derasa seldom come in nice colours.. mainly brown or gold.....
Anyway the most sought after clam species is maxima... Coloured ones like crocea demand lots of light to be nice in color but IMO thwey are hardier than crocea........
Me no expert but just my 2cents