Final answer:
The crayfish would be attracted to the magnet due to the iron filing serving as a statolith being influenced by the magnetic field, altering the crayfish's sense of balance and causing movement toward the magnetic source.
Step-by-step explanation:
If crayfish are raised in a very clean aquarium that has only iron filings in the floor, and they are allowed to go through several molts so that an iron filing is now serving as a statolith, the effect of a large magnet suspended above the aquarium is that the crayfish would be attracted to the magnet. This is because the iron filing, now a statolith, would interact with the magnetic field. Statoliths are small granules within the sensory organs of crayfish that help them with equilibrium and sensing orientation. When these statoliths are replaced by or bound to iron filings, as in the scenario, the magnet would have a direct effect on the crayfish's sense of balance and orientation, likely causing them to move toward the magnet in response to the magnetic attraction.
The usual function of a statolith is to assist the crayfish in maintaining its equilibrium by relaying information about its position relative to gravity. In this experimental setup, the magnetic field produced by the magnet would exert a force on the iron filing statolith, essentially pulling on the sensory organ that contains it. As such, the crayfish's response would most likely be oriented towards the source of this new 'gravitational' pull, which in this case is the magnet itself. Therefore, the correct answer would be (d) Crayfish would be attracted to the magnet.