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Hypoathroid
The term hypoathroid (Ancient Greek ''hypo-'', "under" + ''-athroid'', "gathered together") is used to describe the arrangement of ganglia in the nervous system of molluscs. In the hypoathroid state, the pleural ganglia of the "chest" and the pedal ganglia of the "feet" lie close to each other more or less underneath the gut, and they communicate with the cerebral ganglia via long connectives. It is a condition that is characteristic of the Archaeogastropoda clade, and represents one end of a three-part spectrum of such arrangements, the other two being the dystenoid system in which the pleural and cerebral ganglia are closer together but still distinctly separate, and the epiathroid condition in which the pleural, pedal, and cerebral ganglia all lie close together (characteristic, for example, of the Mesogastropoda and Neogastropoda Neogastropoda is an order of sea snails, both freshwater and marine gastropod molluscs. Description The available fossil record of Neogas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epiathroid
The term epiathroid (Ancient Greek ''epi-'', "above" + ''-athroid'', "gathered together") is used to describe the arrangement of ganglia in the nervous system of molluscs. In the epiathroid state, the pleural ganglia of the "chest" and the pedal ganglia of the "feet" lie close to the cerebral ganglia of the "head" forming a neural cluster which begins to approximate a brain. It is a condition characteristic of the Mesogastropoda and Neogastropoda, and is the obverse of the more-primitive hypoathroid condition in which the pleural and pedal ganglia lie close together under the animal's gut and communicate with the cerebral ganglia via long connectives. The Archaeogastropoda clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ... is described as "hypoathroid", and is the clade close ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dystenoid
A dystenoid nervous system is an arrangement of ganglia in the anterior region of some molluscs in which the cerebral and pleural ganglia are situated closer to each other than they are in those molluscs with the more archaic hypoathroid nervous system but still farther apart than those animals with an evolutionarily more recent epiathroid nervous system. Examples of animals having dystenoid systems include '' Macleaniella moskalevi'', '' Teuthirustria cancellata'', and '' Fedikofella caymanensis'' (weakly dystenoid in all three). These are deep sea limpets belonging to the superfamily Cocculinoidea The Cocculinoidea is a superfamily of deepwater limpets (marine gastropods), the only superfamily in the order Cocculinida , one of the main orders of gastropods according to the taxonomy as set up by ( Bouchet & Rocroi, 2005). The clade Coccil .... References {{reflist Mollusc anatomy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ganglia
A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively. A pseudoganglion looks like a ganglion, but only has nerve fibers and has no nerve cell bodies. Structure Ganglia are primarily made up of somata and dendritic structures which are bundled or connected. Ganglia often interconnect with other ganglia to form a complex system of ganglia known as a plexus. Ganglia provide relay points and intermediary connections between different neurological structures in the body, such as the peripheral and central nervous systems. Among vertebrates there are three major groups of ganglia: *Dorsal root ganglia (also known as the spinal ganglia) contain the cell bodies of se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mollusca
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. They are highly diverse, not just in size and anatomical structure, but also in behaviour and habitat. The phylum is typically divided into 7 or 8 taxonomic classes, of which two are entirely extinct. Cephalopod molluscs, such as squid, cuttlefish, and octopuses, are among the most neurologically advanced of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrate species. The gastropod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Archaeogastropoda
Archaeogastropoda (also known as Aspidobranchia) was a taxonomic order of sea snails used in older classifications of gastropods, i.e. snails and slugs. Archeogastropoda are marine prosobranch gastropod mollusks, mainly herbivores, typically having two gills and a double-chambered heart, with the eggs and sperm discharged directly into the water. They were traditionally regarded as a relatively primitive group. This older classification of the gastropods is based on the classification of Johannes Thiele (1925). This classification was not based on true phylogenetic relationships, but on more general affinities between the groups. In the last few years, two new cladistic taxonomies of the gastropods have been published (in 1997 and 2005). This has led to an extensive reclassification of gastropod taxa. The taxon Archaeogastropoda was found to be a paraphyletic group, and therefore unacceptable in a strictly cladistic classification. In the 1997 classification, most of the former ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, the equivalent Latin term ''cladus'' (plural ''cladi'') is often used in taxonomical literature. The common ancestor may be an individual, a population, or a species (extinct or extant). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic. Some of the relationships between organisms ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesogastropoda
Mesogastropoda was for many years a traditional taxonomic group of snails, an order. The order was composed mostly of sea snails, but it also included some land snails and freshwater snails, all of which were prosobranch gastropod mollusks. This order was introduced by J. Thiele in his work from 1921, it and was used for many decades subsequently. Recent research in malacology however has made it clear that ''Mesogastropoda'' was not a monophyletic taxon, and because of that, the taxon is no longer included in modern classifications. Nonetheless most of the standard texts and field guides on mollusks date from the time period when this classification was still current, and therefore references to mesogastropods or Mesogastropoda are frequently encountered. The lower taxa that were traditionally contained in Mesogastropoda are now mostly placed in the superorder Caenogastropoda. A more detailed account of the taxonomy is given in the articles on Gastropoda and Archaeogastropod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neogastropoda
Neogastropoda is an order of sea snails, both freshwater and marine gastropod molluscs. Description The available fossil record of Neogastropoda is relatively complete, and supports a widely accepted evolutionary scenario of an Early Cretaceous origin of the group followed by two rapid diversification rounds in the late Cretaceous and the Paleocene. These sea snails only have one auricle, one kidney and one monopectinate gill, i.e. the gill filaments develop on only one side of the central axis. The shell has a well-developed siphonal canal. The elongated trunk-like siphon is an extensible tube, formed from a fold in the mantle. It is used to suck water into the mantle cavity. At the base of the siphon is the bipectinate (branching from a central axis) osphradium, a sensory receptacle and olfactory organ, that is more developed than the one in the Mesogastropoda. They achieved important morphological changes including e.g., the elongation of the siphonal canal, a shift ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
