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Streptoneural
Streptoneury or chiastoneury is a plesiomorphic condition present in all gastropods which is a result of an evolutionary event called torsion in which the intestines, heart, nephridia, gills, and nerve cords "twist" causing some organs to migrate from the animal's left to its right in order to accommodate the relocation of the mantle cavity close to the animal's head. Specifically, streptoneury is the crossing of the cerebrovisceral connectives caused by this torsion. In a streptoneurous animal, the right visceral nerve becomes a supraintestinal nerve (i.e., moving up from its former position along the intestines on the right side) and the left visceral nerve becomes a subintestinal nerve (i.e., moving down below the intestines and shifting to the right). The extant gastropod molluscs can be described as streptoneurous. However, some lineages, especially the opisthobranchs, have reversed this twist secondarily. The term for this event is ''detorsion'', and the condition in a d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Torsion (gastropod)
Torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle, and shell 180˚ with respect to the head and foot of the gastropod. This rotation brings the mantle cavity and the anus to an anterior position above the head. In some groups of gastropods ( Opisthobranchia) there is a degree of secondary detorsion or rotation towards the original position; this may be only partial detorsion or full detorsion. The torsion or twisting of the visceral mass of larval gastropods is not the same thing as the spiral coiling of the shell, which is also present in many shelled gastropods. Development There are two different developmental stages which cause torsion. The first stage is caused by the development of the asymmetrical velar/foot muscle which has one end attached to the left side of the shell and the other end has fibres attached to the left side of the foot and head. At a certain point in larva ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Streptoneury
Streptoneury or chiastoneury is a plesiomorphic condition present in all gastropods which is a result of an evolutionary event called torsion in which the intestines, heart, nephridia, gills, and nerve cords "twist" causing some organs to migrate from the animal's left to its right in order to accommodate the relocation of the mantle cavity close to the animal's head. Specifically, streptoneury is the crossing of the cerebrovisceral connectives caused by this torsion. In a streptoneurous animal, the right visceral nerve becomes a supraintestinal nerve (i.e., moving up from its former position along the intestines on the right side) and the left visceral nerve becomes a subintestinal nerve (i.e., moving down below the intestines and shifting to the right). The extant gastropod molluscs can be described as streptoneurous. However, some lineages, especially the opisthobranchs, have reversed this twist secondarily. The term for this event is ''detorsion'', and the condition in a d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Symplesiomorphy
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and synapomorphy, all mean a trait shared between species because they share an ancestral species. Apomorphic and synapomorphic characteristics convey much information about evolutionary clades and can be used to define taxa. However, plesiomorphic and symplesiomorphic characteristics cannot. The term ''symplesiomorphy'' was introduced in 1950 by German entomologist Willi Hennig. Examples A backbone is a plesiomorphic trait shared by birds and mammals, and does not help in placing an animal in one or the other of these two clades. Birds and mammals share this trait because both clades are descended from the same far distant ancestor. Other clades, e.g. snakes, lizards, turtles, fish, frogs, all have backbones and none are either birds nor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gastropoda
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. There are many thousands of species of sea snails and slugs, as well as freshwater snails, freshwater limpets, and land snails and slugs. The class Gastropoda contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian. , 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without a fossil record. Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum, with 65,000 to 80,000 living snail and slug species. The anatomy, behavior, feeding, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nephridium
The nephridium (plural ''nephridia'') is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Nephridia come in two basic categories: metanephridia and protonephridia. All nephridia- and kidney- having animals belong to the clade Nephrozoa. Metanephridia A metanephridium (''meta'' = "after") is a type of excretory gland found in many types of invertebrates such as annelids, arthropods and mollusca. (In mollusca, it is known as the Bojanus organ.) A metanephridium typically consists of a ciliated funnel opening into the body cavity, or coelom connected to a duct which may be variously glandularized, folded or expanded (vesiculate) and which typically opens to the organism's exterior. These ciliated tubules pump water carrying surplus ions, metabolic waste, toxins from food, and useless hormones out of the organism by directing them ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mantle (mollusc)
The mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial) is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself. In many species of molluscs the epidermis of the mantle secretes calcium carbonate and conchiolin, and creates a shell. In sea slugs there is a progressive loss of the shell and the mantle becomes the dorsal surface of the animal. The words mantle and pallium both originally meant cloak or cape, see mantle (vesture). This anatomical structure in molluscs often resembles a cloak because in many groups the edges of the mantle, usually referred to as the ''mantle margin'', extend far beyond the main part of the body, forming flaps, double-layered structures which have been adapted for many different uses, including for example, the siphon. Mantle cavity The ''mantle cavity'' is a central fea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Connective Fiber
Connective may refer to: * Connective tissue * Discourse connective, in linguistics, a word or phrase like "therefore" or "in other words". * Logical connective * In the stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ... of flowers, the sterile tissue that connects the anther chambers to one another and to the filament See also * Connection (other) {{disambiguation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opisthobranch
Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopisthobranchia is a taxon containing a revised collection of opisthobranchs, and that taxon is considered monophyletic. Euopisthobranchia does not include some "traditional" opisthobranchs such as the Sacoglossa and the Acochlidiacea. The subclass Heterobranchia now contains all the species which used to be assigned to Opisthobranchia, plus all the species in the Pulmonata. The subclass Opisthobranchia included species in the order Cephalaspidea (bubble shells and headshield slugs), the sacoglossans, anaspidean sea hares, pelagic sea angels, sea butterflies, and many families of the Nudibranchia. ''Opisthobranch'' means "gills behind" (and to the right) of the heart. In contrast, ''Prosobranch'' means ''gills in front'' (of the heart). Opist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Euthyneury
Euthyneury is a plesiomorphic condition present in some gastropods which is a result of two evolutionary events. The first event, which was experienced by the ancestors of all extant gastropods, is known as torsion. Torsion describes the event in which the intestines, heart, nephridia, gills, and nerve cords "twisted" causing some organs to migrate from the animal's left to its right in order to accommodate the relocation of the mantle cavity close to the animal's head. Torsion created a condition in the cerebrovisceral commissures called streptoneury. Secondarily, some gastropod lineages ''detorted'': they reversed the torsion event and straightened out their internal organs, uncrossing the commissures in the process. It is this second state, one in which the commissures have once again become untwisted, that is called ''euthyneury''. The Opisthobranchia Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
