| Olenecoceras | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | incertae sedis |
| Genus: | † Olenecoceras Balashov, 1966 |
| Species: | †O. rastorguense |
| Binomial name | |
| †Olenecoceras rastorguense Balashov, 1966 | |
Olenecoceras is a genus of Middle Cambrian [1] fossils that, once believed to be a cephalopod, has since been excluded from that group (although no alternative classification has been offered). [2] The genus was established by Zakhar Grigor'evich Balashov in 1966, from the river Olenyok. [3]
Octopus relates to approximately 300 species of soft-bodied, eight-limbed molluscs of the order Octopoda. The order is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. Like other cephalopods, an octopus is bilaterally symmetric with two eyes and a beak, with its mouth at the center point of the eight limbs. The soft body can rapidly alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion, by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, and are among the most intelligent and behaviourally diverse of all invertebrates.
Squid are cephalopods in the superorder Decapodiformes with elongated bodies, large eyes, eight arms and two tentacles. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin.
A cephalopod is any member of the molluscan class Cephalopoda 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 modified from the primitive molluscan foot. Fishermen sometimes call cephalopods "inkfish," referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.
The nautilus is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.
Nectocaris pteryx is a species of possible cephalopod known from the "early Cambrian" Emu Bay Shale and Chengjiang biota, the "middle Cambrian" Burgess Shale.
The giant squid is a species of deep-ocean dwelling squid in the family Architeuthidae. It can grow to a tremendous size, offering an example of deep-sea gigantism: recent estimates put the maximum size at around 12–13 m (39–43 ft) for females and 10 m (33 ft) for males, from the posterior fins to the tip of the two long tentacles. The mantle of the giant squid is about 2 m long, and the length of the squid excluding its tentacles rarely exceeds 5 m (16 ft). Claims of specimens measuring 20 m (66 ft) or more have not been scientifically documented.
Spirula spirula is a species of deep-water squid-like cephalopod mollusk. It is the only extant member of the genus Spirula, the family Spirulidae, and the order Spirulida. Because of the shape of its internal shell, it is commonly known as the ram's horn squid or the little post horn squid. Because the live animal has a light-emitting organ, it is also sometimes known as the tail-light squid.
Bigfin squids are a group of rarely seen cephalopods with a distinctive morphology. They are placed in the genus Magnapinna and family Magnapinnidae. Although the family is known only from larval, paralarval, and juvenile specimens, some authorities believe adult specimens have also been seen. Several videos have been taken of animals nicknamed the "long-arm squid", which appear to have a similar morphology. Since none of the seemingly adult specimens has ever been captured or sampled, it remains uncertain if they are of the same genus or only distant relatives.
Nautiloids are a large and diverse group of marine cephalopods (Mollusca) belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus and Allonautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and developed an extraordinary diversity of shell shapes and forms. Some 2,500 species of fossil nautiloids are known, but only a handful of species survive to the present day.
Cameroceras is a genus of extinct, giant orthoconic cephalopod that lived mainly during the Ordovician period. It first appears during the middle Ordovician, around 470 million years ago, and was a fairly common component of the fauna in some places during the period, inhabiting the shallow seas of Laurentia, Baltica and Siberia. Its diversity and abundance became severely reduced following the Ordovician–Silurian extinction events, and the last remnants of the genus went extinct sometime during the Wenlock.
All cephalopods possess flexible limbs extending from their heads and surrounding their beaks. These appendages, which function as muscular hydrostats, have been variously termed arms, legs or tentacles.
Belemnotheutis is an extinct coleoid cephalopod genus from the middle and upper Jurassic, related to but morphologically distinct from belemnites. Belemnotheutis fossils are some of the best preserved among coleoids. Remains of soft tissue are well-documented in some specimens, even down to microscopic muscle tissue. In 2008, a group of paleontologists even recovered viable ink from ink sacs found in several specimens.
Plectronoceras is the earliest known shelled cephalopod, dating to the Late Cambrian. None of the fossils are complete, and none show the apex or aperture of the shell. Approximately half of its shell was filled with septa; 7 were recorded in a 2 centimetres (0.79 in) shell. Its shell contains transverse septa separated by about half a millimetre, with a siphuncle on its concave side. Its morphology matches closely to that hypothesised for the last common ancestor of all cephalopods.
The colossal squid is part of the family Cranchiidae. It is sometimes called the Antarctic squid or giant cranch squid and is believed to be the largest squid species in terms of mass. It is the only recognized member of the genus Mesonychoteuthis and is known from only a small number of specimens. The species is confirmed to reach a mass of at least 495 kilograms (1,091 lb), though the largest specimens—known only from beaks found in sperm whale stomachs—may perhaps weigh as much as 600–700 kilograms (1,300–1,500 lb), making it the largest-known invertebrate. Maximum total length has been estimated at 9–10 metres (30–33 ft).
The cephalopods have a long geological history, with the first nautiloids found in late Cambrian strata, and purported stem-group representatives present in the earliest Cambrian lagerstätten.
Vologdinella is a poorly known genus of extinct animals of uncertain classification with small cylindrical shells. They are known from Middle Cambrian fossils from a Paleozoic limestone in the Chinguiz Mountains of Kazakhstan. The genus was established by Russian paleontologist Zakhar Grigor'evich Balashov in 1962 for a single species, Vologdinella antiqua, which was originally described and illustrated as Orthoceras? antiquus by Aleksandr Grigoryevich Vologdin in 1931.
Belemnitida is an extinct order of squid-like cephalopods that existed from the Late Triassic to Late Cretaceous. Unlike squid, belemnites had an internal skeleton that made up the cone. The parts are, from the arms-most to the tip: the tongue-shaped pro-ostracum, the conical phragmocone, and the pointy guard. The calcitic guard is the most common belemnite remain. Belemnites, in life, are thought to have had 10 hooked arms and a pair of fins on the guard. The chitinous hooks were usually no bigger than 5 mm (0.20 in), though a belemnite could have had between 100 and 800 hooks in total, using them to stab and hold onto prey.
Cephalopod fins, sometimes known as wings, are paired flap-like locomotory appendages. They are found in ten-limbed cephalopods as well as in the eight-limbed cirrate octopuses and vampire squid. Many extinct cephalopod groups also possessed fins. Nautiluses and the more familiar incirrate octopuses lack swimming fins. An extreme development of the cephalopod fin is seen in the bigfin squid of the family Magnapinnidae.
Louise Allcock is a British researcher, best known for her work on ecology and evolution of the cephalopods of the Southern Ocean and deep sea. She is the editor of the Zoological Journal of the Linnean Society.
Richard E. Young is a teuthologist. He is an Emeritus Professor of Oceanography at the University of Hawaii's School of Ocean and Earth Science and Technology.