Living organisms tend to interact with one another in an ecosystem. In ecology, the interaction between two organisms is referred to as SYMBIOSIS. Symbiosis includes different types depending on how beneficial or harmful the relationship is.
One of the symbiotic relationships that occurs in an ecosystem is PARASITISM. Parasitism is the relationship between two organisms in which one organism benefits and the other is harmed due to the actions of the first organism. The organism that benefits is called the PARASITE while the harmed organism is called the HOST.
In this question, the eggs of the marine invertebrate develops in the body of the fish. The developing marine invertebrate feeds on the fish's body in order to derive nourishment. The fish gradually loses nutrients and dies as this prolongs. Hence, the marine invertebrate is benefitting at the expense of the fish. Therefore, the marine invertebrate is a Parasite feeding on a fish host. This makes this kind of relationship PARASITISM. However, since the invertebrate's egg lives and develops INSIDE the fish (host), the relationship is specifically called ENDOPARASITISM.
ExplanatioThe flatworm seems to be the only one benefitting from the relationship because it is using the snail as a host and provides it a place to grow but the snail is being harmed by the worm while doing so. Therefore the relationship is parasitic.
