A squid is a mollusc with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. 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. 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.
Ammonoids are extinct spiral shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living coleoids than they are to shelled nautiloids. The earliest ammonoids appeared during the Devonian, with the last species vanishing during or soon after the Cretaceous–Paleogene extinction event. They are often called ammonites, which is most frequently used for members of the order Ammonitida, the only living group of ammonioids from the Jurassic up until their extinction.
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.
Coleoidea or Dibranchiata, is one of the two subclasses of cephalopods, containing all the various taxa popularly thought of as "soft-bodied" or "shell-less". Unlike its extant sister group Nautiloidea, whose members have a rigid outer shell for protection, the coleoids have at most an internal shell called cuttlebone or gladius that is used for buoyancy or as muscle anchorage. Some species, notably incirrate octopuses, have lost their cuttlebone altogether, while in some it has been replaced by a chitinous support structure. A unique trait of the group is the ability to edit their own RNA.
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the septa (walls) dividing the camerae (chambers). Some older studies have used the term siphon for the siphuncle, though this naming convention is uncommon in modern studies to prevent confusion with a mollusc organ of the same name.
Belemnoids are an extinct group of marine cephalopod, very similar in many ways to the modern squid. Like them, the belemnoids possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length, and no tentacles. The name "belemnoid" comes from the Greek word βέλεμνον, belemnon meaning "a dart or arrow" and the Greek word είδος, eidos meaning "form".
Orthocerida, also known as the Michelinocerida, is an order of extinct orthoceratoid cephalopods that lived from the Early Ordovician possibly to the Late Triassic. A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous, and the Eocene fossil Antarcticeras is sometimes considered a descendant of the orthocerids although this is disputed. They were most common however from the Ordovician to the Devonian.
Aulacocerida is an order of primitive coleoid cephalopods, possibly derived from michelinoceraitids (Orthocerida) early in the Devonian, which in turn gave rise to the Belemnites.
Lingula is a genus of brachiopods within the class Lingulata. Lingula or forms very close in appearance have existed possibly since the Cambrian. Like its relatives, it has two unadorned organo-phosphatic valves and a long fleshy stalk. Lingula lives in burrows in barren sandy coastal seafloor and feeds by filtering detritus from the water. It can be detected by a short row of three openings through which it takes in water (sides) and expels it again (middle).
Boletzkyida is a primitive order of teuthid coleoid cephalopod: the boletzkyids are thought to be the earliest forms of coleoid cephalopods, and appear to form a link between nautiloid orthocerids and more advanced coleoids. Boletzkyida was named and described by Bandel, Reitner, and Sturmer in 1983 (B.R.&S) from specimens found in the Lower Devonian black slate in Germany.
Cylindroteuthis is a genus of belemnite that lived from the Early Jurassic to the Early Cretaceous. Its fossils have been found in Asia, Europe, North America, and New Zealand.
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.
Mollusca is the second-largest phylum of invertebrate animals, after Arthropoda; members are known as molluscs or mollusks. Around 76,000 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.
Acanthoteuthis is a belemnite genus, a squid-like cephalopod with an internal shell from the Late Jurassic Epoch, related to modern coleoids.
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.
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.
Belemnitella bulbosa is a species of belemnite from the Late Cretaceous of North America. It is known only from two localities - the Pierre Shale and Fox Hills Formations. B. bulbosa had a slender somewhat cylindrical rostrum (guard) with a slightly expanded front opening. Like other members of the genus Belemnitella, it had a dorsal ridge on the rostrum. The phragmocone is about the same size or slightly longer than the rostrum and has an oval cross-section.
Paleontology in Delaware refers to paleontological research occurring within or conducted by people from the U.S. state of Delaware. There are no local rocks of Precambrian, Paleozoic, Triassic, or Jurassic age, so Delaware's fossil record does not begin until the Cretaceous period. As the Early Cretaceous gave way to the Late Cretaceous, Delaware was being gradually submerged by the sea. Local marine life included cephalopods like Belemnitella americana, and marine reptiles. The dwindling local terrestrial environments were home to a variety of plants, dinosaurs, and pterosaurs. Along with New Jersey, Delaware is one of the best sources of Late Cretaceous dinosaur fossils in the eastern United States. Delaware was still mostly covered by sea water through the Cenozoic era. Local marine life included manatees, porpoises, seals, and whales. Delaware was worked over by glaciers during the Ice Age. The Cretaceous belemnite Belemnitella americana is the Delaware state fossil.
The Peedee Formation is a geologic formation in North and South Carolina. A marine deposit, named for exposures along the Great Peedee River, it preserves belemnites and foraminifera fossils dating to the Late Cretaceous (Maastrichtian). The formation is notable for its occurrence of Belemnitella americana, known as the Pee Dee Belemnite (PDB), a long-standing standard in stable carbon isotope research. A single pterosaur femur, possibly an Azhdarchid, from the Peedee formation is one of the few pterosaur body fossils found in Eastern North America.
