Question

A sedentary sea anemone gets attached to the shell covering of a hermit crab. This association is
A) Amensalism
B) Ectoparasitism
C) Symbiosis
D) Commensalism

Answer 1

Hint: A truly symbiotic relationship is one where both organisms are benefitting, even if this is to different extents. This may not be very obvious unless the habits of both organisms are known.

Complete Answer:
- In nature, organisms do not exist in isolation. They form many kinds of relations which could be harmful or beneficial to one or both organisms.
- In Amensalism, one of the organisms thrives, while the other is either stunted or destroyed.
- Ectoparasites is a situation in which the parasite lives outside the host’s body. For example, head lice. In this case, only the parasite benefits, the relationship is not mutual, as the parasite gets its nutrition from the host.
- A relationship between organisms has one definite benefit, and the other is not harmed nor does it gain, is commensalism.
- Sea anemones have many stinging cells which are useful both for stunning prey as well as for protection against possible predators. The hermit crab therefore also benefits as it gets protection from predators with the sea anemone attached to its shell. At the same time, the sea anemone is a sedentary organism that feeds depending on what prey floats or swims into its tentacles. As the crab moves along, the anemone has a much greater chance of utilising different food sources. In this relationship, both the anemone as well as the crab benefit. It is therefore a symbiotic relationship.

So the correct answer is (C).

Note: Plants often use commensalism. Many produce seeds which attach to a passing animal via barbs or hooks, and then fall off elsewhere to grow into a new plant far away from the parent.