In 2014, there were new taxonomic and molecular evidence suggesting the presence of two cryptic giant clam species: the Tridacna noae and T. ningaloo. Reports of T. noae first came out when Su et al. (2014) combined both molecular and morphological analysis to distinguish the species from T. maxima. Not long after, the Australian group, Penny & Willan (2014) had also used similar techniques in describing a new species first found in Ningaloo Reef, also named as T. ningaloo.

A wide variety of Tridacna noae specimens with varying tear-drop mantle patterns. Top left clockwise: Christmas Island; Solomon Islands; Yap States; East Timor.

Now a new article published last month ‘rejects’ the new species T. ningaloo, and proposed that it should be regarded as a junior synonym of T. noae. Borsa et al. (2015) has re-examined the molecular data and morphological data for both ‘T. ningaloo‘ and T. noae, and found little molecular differences, except the mantle ornamentation pattern. A further cross-examination of photographs was possible as the authors consulted with the original authors who described T. ningaloo. On this basis, and zoological nomenclature, they recommend that only Tridacna noae should be maintained.


Since its rediscovery, Tridacna noae has captured attention from both scientists and aquarium breeders to now re-look at their T. maxima stocks. While the scientists have been one step behind, the aquarists have had them in their aquariums for quite a while before they were distinguished. My recent visit to Hong Kong brought me to take a quick look (or should I say “market survey”) around their saltwater aquariums. I found at least four giant clam species, including the newly minted Tridacna noae. It shouldn’t come as a surprise to find them in the aquariums, but considering that we are only beginning to investigate the actual distribution of T. noae, it should be relatively ‘easy’ to retrace their origins. 🙂


To help on this, more scientists on the field have began to quantify their distribution and abundance around the Indo-Pacific region, such as two recent studies by Borsa et al. (2015) and Militz et al. (2015).


Another strong piece of evidence on species distinction is that Tridacna noae and T. maxima are reproductively isolated. This meant that breeding between both species is unable to yield viable juveniles. So far, the Taiwanese group at the National Sun Yat-Sen University has made headway examining the reproductive cycles of Tridacna noae found in Taiwan waters. Did you also know that this species is formally described with the first specimen from Taiwan? 🙂

The local Taiwanese Ocean Foundation is currently in the midst of releasing twenty hand-cultured juvenile clams to their local islands! Best of luck to them! 😀

Juvenile giant clams (Tridacna noae and T. maxima) prepared for release in Taiwan waters. Photo by 海洋公民基金會.


I guess one more clam mystery has been solved! 😀

T. ningaloo
Image excerpt from Penny & Willan (2014) – no longer Tridacna ningaloo.