Final answer:
Several species of sea urchins inhabiting the same tide pool practice external fertilization, but seldom interbreed due to a gametic barrier involving chemicals produced by eggs.
Step-by-step explanation:
The given scenario describes an example of a prezygotic barrier known as gametic barrier. In this case, several species of sea urchins inhabit the same tide pool, but they seldom interbreed due to the production of chemicals by eggs that are only attractive to sperm of their own species.