Is this a Crocea or a Squamosa?
TIA
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Neither. It is a Maxima
The article above by James Fatherree is very helpful to use the shell to ID Tridacnid clams. However, often we can only see the mantel of the clams. Color pattern is a good way to IM many clams. Of the common clams, Gigas, Derrasa and Squamosa are easy. Their shape, mantel shape and color pattern are often enough to for ID with a quick glance. Differentiate Crocea, Maxima and Noae sometime require a little more, closer scrutiny.
One of the way I use to ID species of these three clams is shape and position of the afferent and efferent opening. Of these three species, the efferent opening of Maxima is always at the end, while in Noae, the afferent opening is near the mid position, Crocea is a little further along, essentially between the position of the other two species.
Pictures worth more than 1000's words. Here are pictures of three clams, obvious from the color pattern as to the species of them. we can see the relative position of the afferent opening of the three species.
Of course then there are hybrids of the species. Well, we cannot ID all Tridacnid clams. Some hybrid we just need to rely on the seller or genetically ID them.
T. noae. Afferent near mid-line
T. crocea. Afferent farther from mid-line
Maxima. Afferent farthest from mid-line, near the end of the clam.