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Mollusc
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The number of additional fossil species is estimated between 60,000 and 100,000, and the proportion of undescribed species is very high. Many taxa remain poorly studied. Molluscs are the largest marine biology, marine phylum, comprising about 23% of all the named marine organisms. They are highly diverse, not just in size and anatomical structure, but also in behaviour and habitat, as numerous groups are freshwater mollusc, freshwater and even terrestrial molluscs, terrestrial species. The phylum is typically divided into 7 or 8 taxonomy (biology), taxonomic class (biology), classes, of which two are entirely extinct. Cephalopod molluscs, such as squid, cuttlefish, and octopuses, are among the most neurobiology, neurologi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Odontogriphus
''Odontogriphus'' (from , 'tooth' and , 'riddle') is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as in length, ''Odontogriphus'' is a flat, oval bilaterian which apparently had a single muscular foot and a "shell" on its back that was moderately rigid but of a material unsuited to fossilization. Originally it was known from only one specimen, but 189 new finds in the years immediately preceding 2006 made a detailed description possible. (221 specimens of ''Odontogriphus'' are known from the Greater Phyllopod bed, where they comprise 0.42% of the community.) As a result, ''Odontogriphus'' has become prominent in the debate that has gone on since 1990 about the evolutionary origins of molluscs, annelid worms and brachiopods. It is thought that ''Odontogriphus''s feeding apparatus, which is "nearly identical" to ''Wiwaxia''s, is an early version of the molluscan radula, a chitinous "tongue" that bears multiple rows of rasping teeth. He ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halwaxiida
Halwaxiida or halwaxiids is a proposed clade equivalent to the older orders Sachitida He 1980 and Thambetolepidea Jell 1981, loosely uniting scale-bearing Cambrian animals, which may lie in the stem group to molluscs or lophotrochozoa. Some palaeontologists question the validity of the Halwaxiida clade. Definition and members The name "halwaxiid" was formed by combining the names of two members of the proposed group, '' Halkieria'' and '' Wiwaxia''. The group was defined as a set of Early to Mid Cambrian animals that had: a "chain mail" coat of three concentric bands of small armor plates that are called sclerites; in some cases, a small cap-like shell at the front end and in some cases both ends. Some scientists are unhappy with this loose definition, arguing that such traits may have arisen convergently rather than being inherited from a common ancestor. This objection implies that the group may not be monophyletic, and that their similarities are not biologically equivale ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalopoda
A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles ( muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by ''Nautilus'' and ''Allonautilus''. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been iden ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halkieriidae
The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is ''Halkieria'' , which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages. The best known species is ''Halkieria evangelista'', from the North Greenland Sirius Passet Lagerstätte, in which complete specimens were collected on an expedition in 1989. The fossils were described by Simon Conway Morris and John Peel in a short paper in 1990 in the journal ''Nature (journal), Nature''. Later a more thorough description was undertaken in 1995 in the journal ''Philosophical Transactions of the Royal Society of London'' and wider evolutionary implications were posed. The group is sometimes equated to Sachitida, although as originally envisaged, this group includes the wiwaxiids and is thus equivalent to the Halwaxiida. History of discovery Armor plates called "sclerites" had long been known ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kimberella
''Kimberella'' is an extinct genus of marine bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the gastropods, although its affinity with this group is contentious. Specimens were first found in Australia's Ediacara Hills, but recent research has concentrated on the numerous finds near the White Sea in Russia, which cover an interval of time from . As with many Ediacara biota, fossils from this time, its evolutionary relationships to other organisms are hotly debated. Paleontologists initially classified ''Kimberella'' as a type of Cubozoan, but, since 1997, features of its anatomy and its association with scratch marks resembling those made by a radula have been interpreted as signs that it may have been a mollusc. Although some paleontologists dispute its classification as a mollusc, it is generally accepted as being at least a bilaterian. The classification of ''Ki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scaphopoda
Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class of shelled marine invertebrates belonging to the phylum Mollusca with worldwide distribution and are the only class of exclusively infaunal marine molluscs. Shells of species within this class range in length (with ''Fissidentalium metivieri'' as the longest). Members of the order Dentaliida tend to be larger than those of the order Gadilida. These molluscs live in soft substrates offshore (usually not intertidally). Because of this subtidal habitat and the small size of most species, many beachcombers are unfamiliar with them; their shells are not as common or as easily visible in the beach drift as the shells of sea snails and clams. Molecular data suggest that the scaphopods are a sister group to the cephalopods, although higher-level molluscan phylogeny remains unresolved. Cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wiwaxia
''Wiwaxia'' is a genus of soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. ''Wiwaxia'' fossils—mainly isolated scales, but sometimes complete, articulated fossils—are known from early Cambrian and middle Cambrian fossil deposits across the globe. The living animal would have measured up to when fully grown, although a range of juvenile specimens are known, the smallest being long. ''Wiwaxia'' affinity has been a matter of debate: Researchers were long split between two possibilities. On the one hand, its rows of scales looked superficially similar to certain scale worms (annelids); conversely, its mouthparts and general morphology suggested a relationship to the shell-less molluscs. More recently, evidence for a molluscan affinity has been accumulating, based on new details of ''Wiwaxia'' mouthparts, scales, and growth history. The name derives from Wiwaxy Peak in British Columbia. The proposed clade Halwaxiida con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Monoplacophora
Shell of Monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic class of molluscs with a cap-like shell, inhabiting deep sea environments. Extant representatives were not recognized as such until 1952; previously they were known only from the fossil record, and were thought to have become extinct 375 million years ago. Although the shell of many monoplacophorans is limpet-like in shape, they are not gastropods, nor do they have any close relation to gastropods. Definition Discussion about monoplacophorans is made difficult by the slippery definition of the taxon; some authors take it to refer to all non-gastropod molluscs with a single shell, or all single-shelled molluscs with serially repeated units; whereas other workers restrict the definition to cap-shaped forms, excluding spiral and other shapes of shell. The inclusion of the gastropod-like Bellerophontoidea within the group is also contentious. One attempt to resolve this confusion was to separ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acaenoplax
''Acaenoplax'' is an extinct worm-shaped mollusc known from the Coalbrookdale Formation of Herefordshire, England. It lived in the Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ... period. It was a couple of centimetres long and half a centimetre wide, and comprises serially repeated units with seven or eight shells, and rings of 'spines'. Some of its characters are reminiscent of the polychaete worms, and the character combinations do not place it obviously in the stem of any modern mollusc group, but although it was originally interpreted as a polychaete, this position is untenable for a number of reasons. Morphology The organism resembles a bristled worm, but bears a number of shells on its upper surface. The first shell is cap-like, whereas the others are saddl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Littorina Littorea
The common periwinkle or winkle (''Littorina littorea'') is a species of small edible whelk or sea snail, a marine gastropod mollusc that has gills and an operculum, and is classified within the family Littorinidae, the periwinkles. This is a robust intertidal species with a dark and sometimes banded shell. It is native to the rocky shores of the northeastern, and introduced to the northwestern, Atlantic Ocean. Description The shell is broadly ovate, thick, and sharply pointed except when eroded. The shell contains six to seven whorls with some fine threads and wrinkles. The color varies from grayish to gray-brown, often with dark spiral bands. The base of the columella is white. The shell lacks an umbilicus. The white outer lip is sometimes checkered with brown patches. The inside of the shell is chocolate brown. The width of the shell ranges from at maturity, with an average length of . Shell height can reach up to , [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solenogastres
The Solenogastres (less often referred to as Neomeniomorpha), common name, commonly known as solenogasters, are a class of small, worm-like, shell-less Mollusca, molluscs (Aplacophora), the other class being the Caudofoveata (Chaetodermomorpha).MolluscaBase eds. (2021). MolluscaBase. Solenogastres. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=2094 on 2021-04-14 Some recent literature and recent molecular evidence, indicates that the Aplacophora may be polyphyletic, and therefore some taxonomists may divide Solenogastres and Caudofoveata into separate classes. Morphology In contrast to many other mollusc classes, aplacophorans have no shell, and are instead covered by aragonite, aragonitic sclerites (calcareous wikt:spicule, spicules), which can be solid or hollow. These spicules can be arranged perpendicular to one another within the cuticle to form a skeleton, stick up to form a palisade, or can lie flat against th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aculifera
Aculifera (older name: Amphineura) is a clade of molluscs incorporating those groups that have no conch or shell, that is, the Polyplacophora, Caudofoveata and Solenogastres. For a summary, see It is a sister group to the Conchifera. Monophyly of Aculifera is supported by fossil, anatomical and molecular studies. The oldest known aculiferan is '' Qaleruaqia'', which was found in the Aftenstjernesø Formation in Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ..., which dates back to the Cambrian Stage 4. References Mollusc taxonomy {{mollusc-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
