Copepods

There are over 1,000 species of parasitic copepods. As larva—or nauplia—most look and act like typical copepods. It is only later, when the parasites reach various stages in their development, that they begin to attach themselves to a host creature and radically change in appearance. In fact, many of the adult parasitic copepods are incredibly deviant in physical structure from their free-living relatives. Indeed, it is nearly impossible to find a single trait that is common to all copepods, both free-living and parasitic. One of the only characteristics that they tend to share is that the females have egg sacs which secrete a sticky liquid when the eggs are laid, gluing them together.

Furthermore, parasitic copepods are vastly different in appearance from other crustaceans. In general, adult parasitic copepods are shapeless, having neither limbs nor antennae and sometimes no body segments. Because these creatures start their lives as free-living animals, scientists infer that their ancestors were free-living and that they only evolved parasitic behavior after their environments dictated it.

Parasitic copepods can inflict severe damage on their hosts. This damage is often worsened by the presence and infestation of accompanying fungi.