The subject of this aquarium macro image is the exhalent siphon of a tridacnid clam photographed under pure actinic light. Found in intensely illuminated reef environments, Tridacnids are interesting in that they derive the vast majority of their food purely from the process of photosynthesis. Like many corals, the clams use zooxanthellae in their mantle tissues to achieve this. The colourful mantle also contains fixed cells called ‘iridophores’ that contain fluorescent pigments (we can see these cells lining the wall of the siphon in the image). The iridophores main function is to protect the clam against UV radiation.

John Clipperton, Cheshire