The Aspidogastrea (gr. aspid - shield, gaster - stomach/pouch) 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 mm to several cm. They are parasites of freshwater and marine molluscs and vertebrates (cartilaginous and bony fishes and turtles). 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. Fluke is: Another name for trematodes, a kind of flatworm (for example, the Liver Fluke). ... In biology, a species is a kind of organism. ... In object-oriented programming, subclass is a class that is derived from another class or classes. ... Orders not necessarily a complete list Azygiida Echinostomida Opisthorchiida Plagiorchiida Strigeata Strigeatida Trematodes are also known as flukes. ... Orders within the Digenea Strigeidida Azygiida Echinostomida Plagiorchiida Opisthorchiida The digenea (Gr. ... A parasite is an organism that lives in or on the living tissue of a host organism at the expense of it. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... France Marines is the name of a commune in the département of Val dOise, France. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Orders see text The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage. ... Orders See text The Actinopterygii are the ray-finned fish. ... Atlantic herring, Clupea harengus, the most abundant fish species in the world. ... Families See text Turtles are reptiles of the order Testudinata, most of whose body is shielded by a special bony shell developed from their ribs. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Economics (in Greek Οικονομικά) derives from the Greek word Eco(οίκω=house) and nemo(νέμω=distribute) is the social science that studies the allocation of scarce resources through measurable variables. ... A biologist is a scientist devoted to and producing results in biology through the study of organisms. ... Adjective archaic (more archaic, most archaic) From an earlier period and no longer in common use; of or characterized by antiquity or archaism, antiquated. ...

Morphology

Shared characteristics

Shared characteristics of the group are a large ventral disc with a large number of small alveoli ("suckerlets") or a row of suckers and a tegument with short protrusions, so-called "microtubercles". In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... The alveoli (singular:alveolus), tiny hollow sacs which are continuous with the airways, are the sites of gas exchange with the blood. ...

Larval physiology

Larvae of some species have ciliated patches. Those of Multicotyle purvisi have four patches on the anterior side of the posterior sucker and six at the posterior side, those of Cotylogaster occidentalis have an anterior ring of eight and a posterior ring of six, while larvae of Aspidogaster conchicola, Lobatostoma manteri, Rugogaster hydrolagi lack cilia altogether. Larvae of some species hatch from eggs, others do not. Larvae are the plural of larva, juvenile form of animals with indirect development. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ...

Excretory system

Like most platyhelminthes, aspidogastreans use flame cells as an excretory mechanism. The two excretory bladders are located dorsally, on the anterior side of the posterior sucker, connected to ducts, and three flame cell "bulbs" on each side of the body; the ducts contain cilia to aid the flow of excreta. Classes Monogenea Trematoda Cestoda Turbellaria The flatworms (Platyhelminthes, Greek platy: flat; helminth: worm) are a phylum of relatively simple soft-bodied invertebrate animals. ... Excretion is the biological process by which an organism separates waste products from its body. ... A bladder is a pouch or other flexible enclosure with waterproof or gasproof walls. ... The contents of this page have been moved to http://en. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ...

Nervous system

Aspidogastreans have a nervous system of extraordinary complexity, greater than that of related free-living forms, and a great number of sensory receptors of many different types. The nervous system is of great complexity, consisting of a great number of longitudinal nerves (connectives) connected by circular commissures. The brain (cerebral commissure) is located dorsally, in the anterior part of the body, the eyes dorsally attached to it. A nerve from the main connective enters the pharynx and also supplies the intestine. Posteriorly, the main connective enters the sucker. The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and processes input from the senses, and initiates actions. ... Senses are the physiological methods of perception. ... Receptor may refer to: In telecommunication, a receiver. ... A nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. ... In the anatomy of animals, the brain, or encephalon, is the supervisory center of the nervous system. ... Diagram of a human eye. ...

Sensory receptors are scattered over the ventral and dorsal surface, the largest numbers occurring on the ventral surface, at the anterior end and on the posterior sucker. Electron-microscopic studies revealed 13 types of receptors (Rohde and Watson, 1990a, b, c) The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. ...

Life cycles

Their life cycle is much simpler than that of digenean trematodes, including a mollusc and a facultative or compulsory vertebrate host. There are no multiplicative larval stages in the mollusc host, as known from all digeneans. Life cycle refers to: Biological life cycle New product development Honeybee life cycle This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Orders within the Digenea Strigeidida Azygiida Echinostomida Plagiorchiida Opisthorchiida The digenea (Gr. ... Orders not necessarily a complete list Azygiida Echinostomida Opisthorchiida Plagiorchiida Strigeata Strigeatida Trematodes are also known as flukes. ... Classes Caudofoveata Aplacophora Polyplacophora - Chitons Monoplacophora Bivalvia - Bivalves Scaphopoda - Tusk shells Gastropoda - Snails and Slugs Cephalopoda - Squids, Octopuses, etc. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ...

Host specificity of most aspidogastreans is very low, i.e., a single species of aspidogastrean can infect a wide range of host species, whereas a typical digenean trematode is restricted to few species (at least of molluscs). For example, Aspidogaster conchicola infects many species of freshwater bivalves belonging to several families, as well as snails, many species of freshwater fishes of several families, and freshwater tortoises (Rohde, 1972). For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... Orders Subclass Protobranchia Solemyoida Nuculoida Subclass Pteriomorphia - oysters Arcoida Mytiloida Pterioida Subclass Paleoheterodonta - mussels Trigoinoida Unionoida Subclass Heterodonta - clams, zebra mussels Veneroida Myoida Subclass Anomalosdesmata Pholadomyoida Animals of the Class Bivalvia are known as bivalves because they typically have two-part shells, with both parts being more or less symmetrical. ... Giant African Snail (Achatina fulica) The name snail applies to most members of the molluscan Class Gastropoda that have coiled shells. ... Atlantic herring, Clupea harengus, the most abundant fish species in the world. ... Genera Chersina Dipsochelys Furculachelys Geochelone Gopherus Homopus Indotestudo Kinixys Malacochersus Manouria Psammobates Pyxis Testudo Tortoise is the name given to the land-dwelling reptiles most of whose body is shielded by a special shell. ...

Life cycles have been elucidated for a number of species. Lobatostoma manteri is an example of a species which has obligate vertebrate hosts. Adult worms live in the small intestine of the snubnosed dart, Trachinotus blochi (Teleostei, Carangidae), on the Great Barrier Reef. They produce large numbers of eggs which are shed in the faeces. If eaten by various prosobranch snails, larvae hatch in the stomach, and - depending on the species of snail - stay there or migrate to the digestive gland where they grow up to the preadult stage which has all the characteristics of the adult including a testis and ovary (Rohde, 1973). A worm is an elongated soft-bodied invertebrate animal. ... Diagram showing the small intestine In biology the small intestine is the part of the gastrointestinal tract between the stomach and the large intestine (colon). ... Orders See text The Actinopterygii are the ray-finned fish. ... Satellite image of a part of the Great Barrier Reef. ... Wiktionary has a definition of: Egg Egg has multiple meanings. ... Feces (also spelled faeces or fæces) are the waste products from the digestive tract expelled through the anus during defecation. ... Giant African Snail (Achatina fulica) The name snail applies to most members of the molluscan Class Gastropoda that have coiled shells. ... In anatomy, the stomach (in ancient Greek στομάχι) is an organ in the alimentary canal used to digest food. ... Migration occurs when living things move from one biome to another. ... Digestion is the process whereby a biological entity processes a substance, in order to chemically convert the substance into nutrients. ...

Evolutionary relationships

Digenean trematodes have been cultured in various, complex, media. However, their parasitic stages die soon in water. Aspidogastreans may survive for many days or even weeks outside a host in simple physiological saline solution). For example, adult A. conchicola survived in water for a fortnight, and in a mixture of water and saline solution for up to five weeks. L. manteri extracted from fish could be kept alive for up to 13 days in dilute sea water in which they laid eggs containing larvae infective to snails (Rohde, 1972). This has led to the suggestions that aspidogastreans are archaic trematodes, not yet well adapted to specific hosts, which have given rise to the more "advanced" digenean trematodes, and that the complex life cycles of digenean trematodes have evolved from the simple ones of aspidogastreans The word culture comes from the Latin root colere (to inhabit, to cultivate, or to honor). ... Saline may refer to: Salinity Saline (medicine) Saline, Michigan Saline, Scotland - a village in the burgh of Fife, Scotland. ... Atlantic herring, Clupea harengus, the most abundant fish species in the world. ... Adjective archaic (more archaic, most archaic) From an earlier period and no longer in common use; of or characterized by antiquity or archaism, antiquated. ... A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. ...

Synapomorphies of the trematodes are presence of a Laurer's Canal, a posterior sucker (transformed to an adhesive disc in the Aspidogastrea), and life cycles involving molluscs and vertebrates. DNA studies have consistently supported this sister group relationship. The question of whether vertebrates or molluscs are the original hosts of the trematodes, has not been resolved (Rohde, 2001). Shared characteristics that define a cladistic grouping. ...

This view is supported by the evolutionary relationships of the hosts which these two subclasses utilise. The hosts of aspidogastreans include chondrichthyan fishes (sharks, rays and chimaeras), a group that is 450 million years old, whereas the digeneans, are known from teleost fishes (210 million years old) as well as from various "higher" vertebrates; very few species have invaded chondrichthyans secondarily. Orders see text The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage. ... Orders see article text below Sharks are a group (superorder Selachimorpha) of fish, with a full cartilaginous skeleton, a streamlined body plan with between 5 and 7 gill slits along the sides (most often) or side of the head (the first modified slit is behind the eye and called a... Ray has several meanings. ... Families Callorhynchidae Rhinochimaeridae Chimaeridae Other meanings, based on a fantastic animal, are at Chimera Chimaera is the common name of the species in the families Callorhynchidae, Rhinochimaeridae and Chimaeridae which all are closely related to sharks; they are also called ghost sharks. ... Orders See text The Actinopterygii are the ray-finned fish. ...

Families within the Aspidogastrea

Rohde (2001) distinguish four families of Aspidogastrea:

• The Rugogastridae include a single genus, Rugogaster, with two species from the rectal glands of holocephalan fishes. It is characterised by a single row of rugae (transverse thickenings of the body surface), numerous testes, and two caeca. Species of all other families have a single caecum and either one or two testes.

• The Stichocotylidae include the single species Stichocotyle nephropis from the intestine of elasmobranchs. It has a single ventral row of well separated suckers.

• The Multicalycidae include the single genus Multicalyx from the intestine of holocephalans and elasmobranchs. It is characterised by a single ventral row of alveoli.

• The Aspidogastridae includes species infecting molluscs, teleosts and turtles. The ventral adhesive disc bears either three or four rows of alveoli. Rohde distinguishes three subfamilies of Aspidogastridae, the Rohdellinae, Cotylaspidinae and Aspidogastrinae.

Gibson (1987) further recognized two orders, the Aspidogastrida with the single family Aspidogastridae, and the Stichocotylida including the Stichocotylidae, Multicalycidae and Rugogastridae. However, similarities between species of these two orders are so great that distinction at the level of orders does not seem justified. Families Callorhynchidae Rhinochimaeridae Chimaeridae Other meanings, based on a fantastic animal, are at Chimera Chimaera is the common name of the species in the families Callorhynchidae, Rhinochimaeridae and Chimaeridae which all are closely related to sharks; they are also called ghost sharks. ... Human male anatomy The testicles, known medically as testes (singular testis), are the male generative glands in animals. ... In anatomy of the digestive system, the cecum or caecum is a pouch connected to the large intestine between the ileum and the colon. ... Superorders Galeomorpha Batoidea Selachimorpha Elasmobranchii is the subclass of cartilaginous fishes that includes skates, rays and sharks. ... The alveoli (singular:alveolus), tiny hollow sacs which are continuous with the airways, are the sites of gas exchange with the blood. ... The alveoli (singular:alveolus), tiny hollow sacs which are continuous with the airways, are the sites of gas exchange with the blood. ...

References

• Gibson, D. I. (1987). Questions in digenean systematics and evolution. Parasitology 95, 429-460.

• Rohde, K. (1972). The Aspidogastrea, especially Multicotyle purvisi Dawes, 1941. Advances in Parasitology 10, 77 - 151.

• Rohde, K. (1973). Structure and development of Lobatostoma manteri sp. nov. (Trematoda: Aspidogastrea) from the Great Barrier Reef, Australia. Parasitology 66, 63-83.

• Rohde, K. (2001). The Aspidogastrea, an archaic group of Platyhelminthes.In: Interrelationships of the Platyhelminthes, pp. 159-167 (eds. Littlewood, D.T.J. and Bray, R.A.). Taylor and Francis, London and New York.

• Rohde, K. and Watson, N. A. (1990a). Non-ciliate sensory receptors of larval Multicotyle purvisi (Trematoda, Aspidogastrea). Parasitology Research 76, 585-590.

• Rohde, K. and Watson, N. A. (1990b). Uniciliate sensory receptors of larval Multicotyle purvisi(Trematoda, Aspidogastrea). Parasitology Research 76, 591-596.

• Rohde, K. and Watson, N. (1990c). Paired multiciliate receptor complexes in larval Multicotyle purvisi (Trematoda, Aspidogastrea). Parasitology Research 76, 597-601.

External links

• Aspidogastrea from Tree of Life (http://tolweb.org/tree?group=Aspidogastrea&contgroup=Platyhelminthes)
• Checklist of European aspidogastreans (http://erms.biol.soton.ac.uk/lists/brief/Aspidogastrea.shtml)
• Fishdisease.net (http://www.fishdisease.net)