Some marine organisms have developed strategies for defense, and others have developed strategies for attack; this is an example of coevolution in the struggle for survival of the fittest. An example of a defensive strategy can be seen in the barnacle larvae (nauplii) with plates of chitin that weave into a hard shell. An animal with an attacking strategy includes the polychaete worm, some of which have extending jaws hardened with a copper containing biomineral and is able to actively swim and search for prey. Polychaetes generally prey on benthic invertebrates though certain species prey on one another. Nauplii prey on microscopic organisms like copepods or other zooplankton as well as some phytoplankton.
