Adult giant clams are completely sessile, unable to move from their position on the coral reef. They reproduce by expelling sperm and eggs into the sea (6), where fertilization occurs. The fertilised eggs quickly enter a swimming stage, (where they are known as trochophores), before entering a planktonic stage (7). During this stage, the larvae, (known as 'veligers'), inhabit the open ocean for one week, before settling in the substrate. If a clam is disturbed it will close its shell valves (6). Giant clams have an inhalant siphon, which they use to draw in seawater that is then filtered for planktonic food (6). The majority of the clam's nutrients however, are obtained by a mutually beneficial relationship with minute algae known as zooxanthellae (6). These plant-like algae exist in delicate tubules which are extensions of the stomach (8). The algae gain protection from predation by being associated with such a large organism, while the clam obtains the carbon by-products of photosynthesis (9). Giant clams also provide protection for a species of pea crab (Xanthasia murigera
); a single pair will often be found living within the cavity of the clam (5).