According to the passage, the optics of the vent crab Bythograea thermydron (line 4 ) serve all of the following purposes over the course of its life-cycle EXCEPT

A． They assist in the orientation process by helping the crab navigate toward post-larval settlements.
B． They assist the crabs visually by permitting imaging in the light-saturated upper oceanic depths.
C． They help the crabs navigate by providing thermal and chemical senses to the adult crab near post-larval settlements.
D． They increase the crabs' flexibility by allowing the crab to adapt to two different environments with different lighting conditions.
E． They permit the crabs to achieve increased sensitivity to the location of underwater thermal vents.