Context: The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods, respectively. Lapworth, recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, and placed them in a period of their own. It received international sanction in 1960, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress., Campbelloceras is a tarphyceratid nautiloid known from the Lower Ordovician, Upper Canadian Epoch of North America, where it is widespread. "Campbelloceras" was named by Ulrich and Foerste in 1936. , 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 walls dividing the chambers., Trocholites is a tarphycerid genus in the family Trocholitidae from the Middle and Upper Ordovician with a gradually expanding, weakly ribbed shell; whorls in contact, dorsum slightly impressed; cross section depressed, venter and sides rounded; siphuncle close to but not at the dorsal margin. , 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., Tarphyeras is a genus of tarphyceratid with whorls rounded in cross section , having a deeply impressed dorsum and a ventral to subcentral siphuncle , known from the Lower Ord ( U Canad ) of North America . It differs from Campbelloceras in that Campbelloceras is only slightly impressed , from Centrotarphyceras in that Centrotarphyceras is subquadrate and has a central siphuncle , and from Trocholites in that although Trocholites is subcircular in cross section , the siphuncle is subdorsal . Taphyceras may be derived from Campbelloceras through development of tighter coiling and a deeper impression along with a smaller siphuncle that may be further offset from the venter . Tarphyceras was named by Hyatt in 1894 ., The nautilus (from the Latin form of the original Ancient Greek "", 'sailor') is a pelagic marine mollusc of the cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina., 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., A cephalopod (pronounced or ) is any member of the molluscan class Cephalopoda (Greek plural , "kephalópoda"; "head-feet"). 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. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology., Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda, which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone. Despite their name, cuttlefish are not fish but molluscs., A fish is any member of a group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology. The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification., The Trocholitidae are Tarphycerida with whorls in close contact as with the Tarphyceratidae, but in which the siphuncle, similar in structure, becomes dorsal. The Trocholitidae are derived from the Tarphyceratidae, perhaps from different tarphyceratids., Subject: tarphyceras, Relation: parent_taxon, Options: (A) allonautilus (B) animal (C) cephalopoda (D) dorsum (E) hagfish (F) mollusca (G) mya (H) nautiloid (I) nautilus (J) olfactores (K) sepiida (L) spirula (M) tarphyceratidae (N) tarphycerida (O) trocholitidae
Output: tarphyceratidae