Tridacna noae is a newly recognized species of giant clam which reefers have been enjoying in our aquariums for many years now. We’ve always been told that the morphology of the shells of giant clams is the key to identifying species in the genus Tridacna but for once reef aquarists get a lucky break by getting a new species we can identify based on easily distinguished mantle pattern and coloration.
Noah’s giant clam, Tridacna noae, is a species of giant clam very similar to the ubiquitous maxima clam which was first described way back in 1798! Scientists and reef aquarists alike have lumped both maxima and teardrop clams as the same species but new research using genetic analysis was able to differentiate the “cryptic” species from T. maxima based on a number of different gene sequences.
While Tridacna noae may seem like a cryptic species based on morphological differences in the shell’s features, which is an unreliable method of diagnosing Noah’s giant clam from maxima clams, a cursory look at the living mantle of either species can easily help to differentiate the two species apart. As you may have guessed, teardrop clams are unmistakable in their pattern and for this reason we’ve always distinguished maxima and ‘teardrop’ maxima clams from each other simply based on the presence of the teardrop pattern on the mantle.
Once the researchers of the new study were confident that genetic analysis showed two distinct species within T. maxima, they were able to go back and examine the appearance of the living mantle and identify not one but two defining features of T. noae. Noah’s giant clams always show that “T. noae possessed one to several layers of oval patches with different colours bounded by white margins” – this is the pattern we reefers call ‘Teardrops”.
Maxima and Teardrop clams also differ in tat T. maxima always shows a neat row of eyes on the edges of the mantle, whereas these are much more spread out in Tridacna noae, a feature any aquarist with specimens of either species can appreciate in the aquarium right now. As we marine aquarists already know, Teardrop clams have a fairly wide distribution which overlaps with maxima clams; gold teardrop clams are commonly available from Vietnam and blue teardrop clams sporadically appear in the trade from Australia and the Indo-Pacific.
Just a few years ago we featured an incredible and large blue teardrop clam from Australia which we now know is the species Tridacna noae. This new development in the taxonomy of Tridacna giant clams with teardrop clams becoming their own species, together with the bumpy-mantled Tridacna ningaloo really makes us wonder how many more species of giant clams might be out there, and distinguishable based on more acute observations of the mantle’s appearance, color and pattern.
The newly recognized Noah’s Giant Clam which aquarists will simply call Teardprop clams was redescribed by Su, Hung, Kubo & Liu in volume 62 of the Raffles Bulletin of Zoology bringing the total number of giant clam species to 12, with ten total species in the genus Tridacna.