A Small Marine Amphipod Has Recently Been Discovered That Carries

Multiple Choice

A small marine amphipod has recently been discovered that carries another organism on its back. The "backpack" organism tastes bad. If a fish ingests the pair, it immediately spits them back out. If the amphipod is alone, however, it is readily eaten and swallowed. There is no apparent benefit in this relationship for the "backpack" organism, which appears to be neither helped nor harmed. This is therefore a case of

A) mutualism.
B) parasitism.
C) commensalism.
D) competitive exclusion.
E) predation.