Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.
Digenea is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults commonly live within the digestive tract, but occur throughout the organ systems of all classes of vertebrates. Once thought to be related to the Monogenea, it is now recognised that they are closest to the Aspidogastrea and that the Monogenea are more closely allied with the Cestoda. Around 6,000 species have been described to date.
Trematodes are parasitic flatworms of the class Trematoda, specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions.
Echinostoma is a genus of trematodes (flukes), which can infect both humans and other animals. These intestinal flukes have a three-host life cycle with snails or other aquatic organisms as intermediate hosts, and a variety of animals, including humans, as their definitive hosts.
Like humans and other animals, fish suffer from diseases and parasites. Fish defences against disease are specific and non-specific. Non-specific defences include skin and scales, as well as the mucus layer secreted by the epidermis that traps microorganisms and inhibits their growth. If pathogens breach these defences, fish can develop inflammatory responses that increase the flow of blood to infected areas and deliver white blood cells that attempt to destroy the pathogens.
In the 10th edition of Systema Naturae, Carl Linnaeus described the Pisces as:
Always inhabiting the waters; are swift in their motion and voracious in their appetites. They breathe by means of gills, which are generally united by a bony arch; swim by means of radiate fins, and are mostly covered over with cartilaginous scales. Besides the parts they have in common with other animals, they are furnished with a nictitant membrane, and most of them with a swim-bladder, by the contraction or dilatation of which, they can raise or sink themselves in their element at pleasure.
Clinostomum marginatum is a species of parasitic fluke. It is commonly called the "yellow grub". It is found in many freshwater fish in North America, and no fish so far is immune to this parasite. It is also found in frogs. Clinostomum marginatum can also be found in the mouth of aquatic birds such as herons and egrets. They are commonly present in the esophagus of fish-eating birds and reptiles. Eggs of these trematodes are shed in the feces of aquatic birds and released into water. Aquatic birds become hosts of this parasite by ingesting infected freshwater fish. The metacercariae are found right beneath the skin or in the muscles of host fish.
Megalodiscus temperatus is a Digenean in the phylum Platyhelminthes. This parasite belongs to the Cladorchiidae family and is a common parasite located in the urinary bladder and rectum of frogs. The primary host is frogs and the intermediate hosts of Megalodiscus temeperatus are freshwater snails in the genus Helisoma.
Telosentis exiguus is a widespread intestinal parasitic worm. Its hosts are marine and brackish water fish of the Mediterranean basin.
Alaria is a genus of flatworms, or trematodes, in the family Diplostomidae.
Diplostomum pseudospathaceum is a species of trematode in the family Diplostomidae.
Electrovermis zappum is a species of fish blood fluke discovered in the Gulf of Mexico and described in 2019. It has been placed in a new genus, Electrovermis. This parasite infects the lesser electric ray. Once it successfully invades the host, it migrates to and dwells in the lumen of the heart of the ray. Like other blood flukes, it thrives by feeding off of the blood of its host. The adults are morphologically and physiologically similar to other blood flukes that infect rays such as Orchispirium heterovitellatum. Unlike many other blood flukes that infect molluscs as an intermediate host, E. zappum infects bivalves such as clams. Both the rays and clams densely populate warm, shallow intertidal marine waters, which provide the parasite an opportunistic environment to carry out its life cycle stages.
Heterobilharzia is a genus of trematodes in the family Schistosomatidae. The species Heterobilharzia Americana is a parasite of the Southeastern United States and typically found in raccoons. Species of this genus are responsible for Schistosoma in canines. Cercariae found in freshwater may also cause Swimmer's itch in humans.
Trachelobdella lubrica is a species of marine leech in the family Piscicolidae. It is a parasite of fish and has a worldwide distribution in the equatorial belt. It was first described in 1840 by the German zoologist Adolph Eduard Grube, the type locality being Palermo, Sicily, in the Mediterranean Sea.
