Compared to corals, there are only a few giant clam species we get to appreciate in the home aquarium so it’s really exciting when we get new species like Tridacna noae and Tridacna ningaloo, but it’s also super cool to get a closer look at another almost unknown species, Tridacna costata. Only just described in 2008, T. costata was previously considered to be Tridacna maxima in the Red Sea and western Indian Ocean where those two species ranges overlap.
Tridacna costata is unique in that it has a darker, much more textured mantle surface compared to all other species and the folds of its shell are much more pronounced and exaggerated than other species. Furthermore, T. costata can grow much larger than the closely related T. maxima with a realistic maximum size for the latter being around 25cm, about 10 inches, whereas T. costata can often reach shell lengths of 45cm.
This particular series of images made by Nicole Helgason were taken in Mozambique where this species is apparently very common in certain areas. The specimen of T. costata pictured here was observed at a depth of about 9m, or just under 30 feet deep and it is estimated to be about 30cm long, although Ms. Helgason tells us that there are many more and larger specimens in this habitat.
In the image of Tridacna costata below you can see a standard 1Kg dive weight in the image for scale and off to the right side you can just barely make out the mantle of a recognizable T. maxima. This is one of the best and closest pictures we have seen of this enigmatic giant clam species wherein its shell and mantle characteristics can be clearly made out so we can better appreciate what makes this species unique. Huge thanks to Nicole Helgason for sharing these great photographs with us and if you find yourself diving in the tropical western Indian Ocean, do be on the lookout for a giant clam that is much too big to be a maxima.