Tridacnid clam ID made easy

Discussion in 'Reef Aquarium Articles and How To's' started by chrisANDbarb, Nov 9, 2008.

  1. chrisANDbarb

    chrisANDbarb Fire Worm

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    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)

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    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.

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    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)

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    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)

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    T. Squamosa

    Narrow byssal opening that closes with age.

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    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.

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    T. Derasa

    Narrow byssal opening that closes with age.

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    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.

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    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.

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    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.

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    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.