Feature & photos by Pamela Lim.When scientists and marine biologistsmention symbiosis, one can only begin tofathom the relationship between two differentliving creatures that live close together anddepend on each other, each gettingparticular benefifits from the other in order tosurvive. How far you can fathom this featdepends upon what you see and sometimeseven what you experience. If you have seena giant clam in the wild (seabed), you willsee the intricate patterns it has.In the years of underwater exploration, giantclams are fascinating to see. We may knowof Nemo’s (the clownfifish of Finding Nemoanimated movie) relationship with theanemone or the goby with the shrimp but thegiant clams are seldom heard of. They areconsidered ‘vulnerable’ as a specie andlisted as ‘protected’ under the CITES(Convention on International Trade inEndangered Species of Wild Fauna andFlora) trade.This enormous shellfifish (Tridacnasp.) is the largest and heaviest of allthe living molluscs. Like all bivalvemolluscs, the shell consists of twovalves. In the larger giant clamsthese valves cannot closecompletely. The shell is extremely thick andlacks bony plates; when viewed from above,each valve has 4 to 5 inward facingtriangular projections. The mantle (flflesh) ofthe clam is visible between the two shells,and is golden brown or yellow or green,although it may contain so many blue orpurple spots that the overwhelmingimpression is of a beautiful iridescent colour.A number of pale or clear spots on themantle, the soft flfleshy part of the body,which are known as ‘windows,’ function toallow sunlight to fifilter in through the mantle.With this light, the minute algae calledzooxanthellae living in the mantle,photosynthesises and secretes a waste thatbecomes food for the giant clam.The mantle is completely fused with theexception of two holes (or ’siphons’); theinhalant siphon is fringed with sensorytentacles, whilst the exhalent siphon is tube-like and is capable of expelling a largevolume of water if the clam’s shells closesuddenly. Though the siphon enables it to  18 of 2418 of 24Giant Clam (Tridacna sp.)taken in Sarangani Bay,Maasim, Mindanao.SYMBIOTIC RELATIONSHIP