To accurately ID Tridacnids you really need to look at the shell, so that's what we will be doing.

Lets start with the most available clam to us hobbyist T.Crocea

Croceas have the largest/widest byssal opening of all the clams(when compared to overall shell size)



there shell is more symmetrical (short front to back, high bottom to top). the shell can close completely and is relatively smooth, sometimes with scutes at the top edge of the shell. Max size about 6 inches.





T.Maxima

Large byssal opening, but narrower and smaller then Crocea in comparison to the over all size of the shell.(Maxima left, Crocea right)



the shell is more elongated front to back and shorter top to bottom, with pronounced scutes in tight rows all the way down to the base of the shell. Max size about 14 inches (Maxima left, Crocea right)



T. Squamosa

Narrow byssal opening that closes with age.



the shell is symmetrical with length almost the same as height. Very large, widely spaced scutes all the way down to the base. Max size about 18 inches.



T. Derasa

Narrow byssal opening that closes with age.



Smooth, symmetrical shell with 6 or 7 prominent vertical folds (this is the main distinction between Derasa and Gigas) Max size about 25 to 30 inches.



T. Gigas

Narrow byssal opening that closes with age. Smooth symmetrical shell with 4 or 5 prominent vertical folds. Largest of the Tridacnid getting over 48 inches long. sorry no photos because i don't keep them.


Lastly we will cover Hippopus Hippopus because they are available to us.

H. Hippopus

Easiest to tell apart, the shell shape is completely different. Very narrow byssal opening that's flattened and squared off.





somewhat ruff shell that may have nodules. the mantle does not hang over the edge of the shell. Max size about 20 to 25 inches.



H. Hippopus has a relative named H. Porcellanus that i doubt we will ever see in the hobby. Shell characteristics are almost identical but this is one time you need to look at the in-current syphon to tell the difference. H. Porcellanus has tentacles around the in-current syphon and H. Hippopus does not.

That's it!

GREAT thread

chris&barb wrote:
H. Hippopus has a relative named H. Porcellanus that i doubt we will ever see in the hobby. Shell characteristics are almost identical but this is one time you need to look at the in-current syphon to tell the difference. H. Porcellanus has tentacles around the in-current syphon and H. Hippopus does not.

Great post Chris&barb.

after reading this, i wonder i had a H. Hippopus or H. Porcellanus..

Hey Adrain

First i have to comment that the colors in your aquarium are just spectacular

The clam photo you posted is of a H. hippopus. Like i mentioned before, it's all about the shell however i can see enough of the shell to be sure it H. hippopus and not H. porcellanus.

Heres a side by side of the two



If you look at the texture of the shells, the one on the left(H. porcellanus) has a much smoother shell then the one on the right (H. hippopus)

here's two more shell photos of H. hippopus to show how rough the shell is

Im attaching the first photo so you can see it better.

Thanks Chris for your inputs and explanation. i fully understand now

and thanks again for your kind compliments RE my tank.

Hi Chris and Barb,

I was lucky enough to get this clam as a hitch hiker on some live rock.

It is strongly attached to the piece of rock and Amashun & I have been racking our brain as to what species. I think its a maxima but Amashun is leaning towards Squamosa.

Can you identify by this pic?

Thanks

Nam

Hello Nam,


I say it is a maxima as well but can you get a clearer pic of it?


Man I wish I could get a tridacnid as a hitchhiker

Welcome to RAF namn8r

Cant see much, try to get a few clear photos of the shell.

Hey Nam, good to see you here.

Like i said, i can not confirm what clam it is based on the clam mental. my 1st impression it was a maxima, but i'm leading towards to squamosa. But if you could post a picture of the clam shell then we should be able to assist more.

btw, i know that you are setting up a new tank, perhaps you can show us your tank on the tank journal too if you don't mind. Good luck mate

Chat soon
Adrian

the reason for me to say Squamosa is because when i look at your picture on the right hand side of the clam shell, it flods very obvious and the stauts (check spelling) grow out more, so convinced me it is more look like a Squamosa to me and hence i give it a guess. I wasn't quite too sure at the beginning.....

Just found this thread from your sig, Chris. Great info!!!

the more i stay here the more i am going to be a wiz thanks to all you for the info i am a nubie and love to learn more
Regards
MaRvIk

Glad you like it here MaRvIk Make sure you tell your friends about us