The flatworms, flat worms, Platyhelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates, and have no specialised circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both ingestion and egestion ; as a result, the food cannot be processed continuously.
The gastrotrichs, commonly referred to as hairybellies or hairybacks, are a group of microscopic (0.06-3.0 mm), cylindrical, acoelomate animals, and are widely distributed and abundant in freshwater and marine environments. They are mostly benthic and live within the periphyton, the layer of tiny organisms and detritus that is found on the seabed and the beds of other water bodies. The majority live on and between particles of sediment or on other submerged surfaces, but a few species are terrestrial and live on land in the film of water surrounding grains of soil. Gastrotrichs are divided into two orders, the Macrodasyida which are marine, and the Chaetonotida, some of which are marine and some freshwater. Nearly 800 species of gastrotrich have been described.
Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. The foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which mostly runs above the midline and ends a little short of the rear of the body. All species have a proboscis which lies in the rhynchocoel when inactive but everts to emerge just above the mouth to capture the animal's prey with venom. A highly extensible muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, with which they attach to a host.
Mycteroperca bonaci, the black grouper, black rockfish or marbled rockfish, is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the family Serranidae, which also includes the anthias and sea basses. Other fish are sometimes called the black grouper including the similar gag grouper, the misty grouper, and the warsaw grouper. This species is found in the western Atlantic Ocean from the northeastern United States to Brazil.
Oligochaeta is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworms, and freshwater or semiterrestrial microdrile forms, including the tubificids, pot worms and ice worms (Enchytraeidae), blackworms (Lumbriculidae) and several interstitial marine worms.
The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from 1 mm (0.039 in) to large freshwater forms more than 500 mm (20 in) long or terrestrial species like Bipalium kewense which can reach 600 mm (24 in) in length. All the larger forms are flat with ribbon-like or leaf-like shapes, since their lack of respiratory and circulatory systems means that they have to rely on diffusion for internal transport of metabolites. However, many of the smaller forms are round in cross section. Most are predators, and all live in water or in moist terrestrial environments. Most forms reproduce sexually and with few exceptions all are simultaneous hermaphrodites.
Monogeneans, members of the class Monogenea, are a group of ectoparasitic flatworms commonly found on the skin, gills, or fins of fish. They have a direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they have both male and female reproductive structures.
The Aspidogastrea is a small group of flukes comprising about 80 species. It is a subclass of the trematoda, and sister group to the Digenea. Species range in length from approximately one millimeter to several centimeters. They are parasites of freshwater and marine molluscs and vertebrates. Maturation may occur in the mollusc or vertebrate host. None of the species has any economic importance, but the group is of very great interest to biologists because it has several characters which appear to be archaic.
The gregarines are a group of Apicomplexan alveolates, classified as the Gregarinasina or Gregarinia. The large parasites inhabit the intestines of many invertebrates. They are not found in any vertebrates. Gregarines are closely related to both Toxoplasma and Plasmodium, which cause toxoplasmosis and malaria, respectively. Both protists use protein complexes similar to those that are formed by the gregarines for gliding motility and for invading target cells. This makes the gregarines excellent models for studying gliding motility, with the goal of developing treatment options for both toxoplasmosis and malaria. Thousands of different species of gregarine are expected to be found in insects, and 99% of these gregarine species still need to be described. Each insect species can be the host of multiple gregarine species. One of the most-studied gregarines is Gregarina garnhami. In general, gregarines are regarded as a very successful group of parasites, as their hosts are distributed over the entire planet.
The Polycladida represents a highly diverse clade of free-living marine flatworms. They are known from the littoral to the sublittoral zone, and many species are common from coral reefs. Only a few species are found in freshwater habitats.
The brownspotted grouper, also known as the brown spotted reef cod, brown-spotted rockcod, coral grouper or honeycomb cod, is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is part of the family Serranidae, which also includes the anthias and sea basses. It has an Indo-Pacific distribution but in the northern Indian Ocean this distribution is discontinuous. It forms part of a species complex with two closely related species in the genus Epinephelus.
The nematodes, roundworms or eelworms constitute the phylum Nematoda. They are a diverse animal phylum inhabiting a broad range of environments. Most species are free-living, feeding on microorganisms, but there are many that are parasitic. The parasitic worms (helminths) are the cause of soil-transmitted helminthiases.
Nemertodermatida is a class of Acoelomorpha, comprising 18 species of millimetre-sized turbellariform, mostly interstitial worms.
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.
The Dolichomacrostomidae are a family of small basal free-living flatworms, and members of the marine, but also brackish, meiobenthos. The name was coined by Reinhard M. Rieger (1971), who designated the Dolichomacrostomidae as a family within the taxon Macrostomida. There are currently about 40 named species in this family.
The Microstomidae are a family of small basal free-living flatworms, and members of the marine, brackish, freshwater meiobenthos and plankton. There are currently about 40 named species in this family.
Macrostomidae is a family of small basal free-living flatworms, and are found in marine, brackish, and freshwater environments. There are currently about 180 named species in this family.
Urastoma cyprinae is a turbellarian that infects the gills of numerous species. It has been reported as free-living organism in marine mud and on algae. Urastoma cyprinae is reported as an opportunistic mantle inhabitant on the gills of various bivalve species, including the clams Tridacna maxima and Tridacna gigas, and the mussels Mytilus edulis and Mytilus galloprovincialis. They are also found throughout the gill surface of C. virginica and is attracted by mucus that coats the gills of oysters. However, the nature of the host-parasite relationship remains unknown.
Syndesmis longicanalis is a species of marine flatworms endemic to the waters off Kenya. They are commensal symbionts of sea urchins.
Bothrioplana is a genus of freshwater flatworms, the sole genus in the family Bothrioplanidae and order Bothrioplanida.
