Monogeneans are a group of flatworms that are commonly found as ectoparasites on the gills of fish. They use specialized structures called hooks and suckers to attach themselves to their host and feed on their blood or mucus.

Invasion is the stage in a marine parasite's life cycle when it actively enters its host's body. This can occur through various mechanisms, such as penetrating the host's skin or being ingested by the host.

Tapeworms are a group of parasitic flatworms that have a complex life cycle involving multiple hosts. They typically have an asexual stage in one host and a sexual stage in another host.

Parasitism is a type of symbiotic relationship in which one organism (the parasite) benefits at the expense of another organism (the host). The parasite derives nutrients or other resources from the host, often causing harm or discomfort to the host.

Trematodes, also known as flukes, are a group of parasitic flatworms that can manipulate the behavior of their hosts. For example, some trematodes can cause their host to become more active or attracted to light, increasing the chances of the parasite being transmitted to a new host.

Virulence is the term used to describe the degree of harm or damage caused by a marine parasite to its host. It is a measure of the parasite's ability to reduce the fitness or survival of its host.

Some species of flukes, such as the digenean trematode Ribeiroia ondatrae, can castrate their host, preventing it from reproducing. This strategy ensures that the parasite has access to the host's resources for a longer period of time.

Transmission is the process by which a marine parasite moves from one host to another. This can occur through various mechanisms, such as direct contact between hosts, ingestion of contaminated food or water, or via an intermediate host.

Some marine protozoan parasites, such as Myxobolus cerebralis, can form large, cyst-like structures called myxospores in the tissues of their host. These myxospores can contain thousands of infective spores, increasing the chances of transmission to new hosts.

Parasitology is the study of parasites and their interactions with their hosts. It encompasses the study of the biology, ecology, and evolution of parasites, as well as their impact on host populations and ecosystems.

Some species of copepods, such as Caligus rogercresseyi, can mimic the appearance or behavior of their host, making it more difficult for the host to detect and remove the parasite. This strategy increases the chances of the parasite successfully transmitting to new hosts.

Immune evasion is the process by which a marine parasite adapts to its host's immune system, allowing it to evade detection and attack. This can occur through various mechanisms, such as disguising itself as host tissue, suppressing the host's immune response, or rapidly changing its surface proteins.

Some species of flukes, such as Dicrocoelium dendriticum, can alter the behavior of their host, leading to increased transmission to new hosts. For example, D. dendriticum can cause its intermediate host, an ant, to climb to the top of a blade of grass, making it more likely to be eaten by a grazing animal, the parasite's definitive host.

Parasite-host interactions is the study of the interactions between marine parasites and their hosts. It encompasses the study of the mechanisms by which parasites exploit their hosts, the host's defenses against parasites, and the co-evolutionary dynamics between parasites and their hosts.

Sea lice, such as Lepeophtheirus salmonis, can cause severe damage to the gills of fish, leading to respiratory distress and even death. They feed on the blood and mucus of the fish, causing irritation and inflammation of the gills. Heavy infestations of sea lice can result in significant economic losses in aquaculture.