Giant clam ID.

[skinz78]

Clam ID can be quite confusing at times and I myself occasionally see one that gets me wondering. The best way to ID giant clams is to look at the shells. Most importantly the bottom of the shell and the byssal opening.

For instance lets look at the T. crocea, it has the largest opening of any of the giant clams and it is also the smallest clam so it is easy to tell. The opening usually resembles a large teardrop. They are the smallest of the giant clams so the teardrop byssal opening is really pronounced.

The sides of the T. crocea's shell is more symmetrical (short front to back, high bottom to top). The T.crocea shell can close completely and is relatively smooth, sometimes with scutes at the top edge of the shell. Max size about 6 inches. I have seen T. crocea with scutes all the way up the shell, this is more common in farmed T. crocea and some vendors may have tried to pass them off as T. maxea because of the scutes. They top out at a max size of about 6 inches.

T.crocea with scutes all the way up the shell.

For me it is pretty easy to tell a T. crocea by looking at the mantle, most of them are fairly close in resemblance to this one. Seems we get a lot of blue T. crocea imported to us.

Next we have the T. maxima, they are the second smallest of the giant clams.
They have a large byssal opening, but narrower and smaller than T. crocea in comparison to the over all size of the shell.

Also the shell is more elongated from front to back and is shorter top to bottom, with pronounced scutes in tight rows all the way down to the base of the shell. They top out at a max size of about 18 inches.

With the T. maxima's mantle being one of the most colorful to ID just from viewing them top down. They often have quite crazy patterns and this makes it hard.

 

[skinz78]

Next in size is the T. squamosa clam, also known as the ruffled clam due to the large size of the scutes on the shell. T. squamosa also has a teardrop byssal opening when younger but as it gets bigger the opening closes with shell growth.

This T. squamosa was about 4.5" at the time of the pic.

T. squamosa's shell is symmetrical with length almost the same as height. Very large, widely spaced scutes all the way down to the base. Maximum size tops out at about 18 inches.

T. squamosa is often confused with T. maxima when trying to ID from the mantle. Their color variation is very similar although T. squamosa is more commonly seen in gold, purple, green or brown and very very rare to see a blue one. They also have quite a pronounced fringe around the incurrent siphon. Other clams have this but not nearly as pronounced as the T. squamosa. They top out at a max size of about 20 inches.

T. derasa has a very narrow byssal opening that closes with age. When smaller the T. derasa shell is very narrow but gets much wider as it ages and eventually they won't be able to fully close.

T. derasa has a smooth, symmetrical shell with 6 or 7 vertical folds (this is the main distinction between Derasa and Gigas). They can develop scutes but most often they get broken off really easily. They top out at a max size of about 30 inches.

They are fairly hard to ID by looking at the mantle but often they have grain of rice shaped florescent stripes. They also have a fringe around the incurrent siphon and this sets them apart from T. gigas.

T. gigas has a narrow byssal opening that closes with age. Smooth symmetrical shell with 4 or 5 prominent vertical folds. They are the largest of the Tridacnid clams getting over 48 inches in length.

These pic's are old, I had one that I grew from 1.5" to 6" in a year. The growth rate scared me so I sold it.

In this pic it was about 2" and it had actually attached to my Fighting conch. It was quite funny when I noticed my clam kinda hopping across the tank behind the snail.

I didn't get many pic's of it and most aren't that good at all. This is the clam top down when it was about 2.5"

Here it was at 6" right before I sold it.

Last of all there is the Hippopus Hippopus, they are available to us but not many people keep them.

H. Hippopus is the easiest to tell apart of all the giant clams, the shell shape is completely different and closely resembles a horse's hoof. They have a very narrow byssal opening that's flattened and squared off.

H. hippopus has somewhat rough shell that may have nodules. The mantle does not hang over the edge of the shell. They top out at a max size of about 25 inches.

Here is a frontal shot of a H. hippopus clam's mantle, they can have electric looking lines in them and usually have a cammo look to them.