Nautilida Agassiz 1847

Order Nautilida Agassiz, 1847 Diagnosis Exogastrically curved or coiled nautiloids with a conch shape ranging from gyroconic or cyrtoconic to more or less tightly coiled. Shell surface smooth or sculptured with a variety of elements (ribs, nodes, spines, longitudinal ridges or lines). Septa simply domed in most species, with the shape of the whorl profile producing suture lines with variable lobes and saddles. Variations in septal shape with inflexions producing deep lobes in some genera. Septal necks short and straight, rarely slightly widened. Connective rings cylindrical or beaded. Siphuncular or cameral deposits absent. Juvenile conch with cup-shaped initial chamber and narrow siphuncle. Morphological evolution includes the degree of coiling, the shape and size of the juvenile and adult conch and the suture line (after Shimansky 1962; emended). Included suborders Nautilina Agassiz, 1847 (Late Triassic to Recent). Solenochilina Flower, 1950 (Early Carboniferous to Late Permian; 16 genera, 77 species). Liroceratina Flower, 1955 (Early Carboniferous to Late Triassic; 26 Palaeozoic genera, 168 Palaeozoic species). Rutoceratina Flower, 1950 (Early to Middle Devonian). Tainoceratina Shimansky, 1957 (Early Carboniferous to Triassic; 55 Palaeozoic genera, 279 Palaeozoic species). Temnocheilina Flower, 1963 (Late Devonian to Early Permian; 31 genera, 166 species). Domatoceratina subordo nov. (Early Carboniferous to Triassic; 40 Palaeozoic genera, 201 Palaeozoic species). Remarks Shimansky (1962: 115; translated from Russian) characterised the order Nautilida as follows: “Conch nautiliconic, less often gyroceraconic, cyrtoceraconic or trochoceraconic, smooth or sculptured. Suture line variable in structure, often with distinct lobes and saddles, which are usually shallow but sometimes very deep. Septal neck straight, less often slightly widened, as a rule short. Connecting rings from cylindrical to beaded. Siphonal deposits and substantial cameral deposits absent. Embryonic shell with a cuplike initial chamber and a narrow siphuncle which is closed at the base. Development involves mainly the degree of coiling, the form and size of the embryonic and adult shell, and suture line.” (translation in Shimansky 1974) Kummel (1964: K412) gave the following short statement: “Curved to coiled conchs presenting majority of mid-Paleozoic nautiloids. [Tainocerataceae and Trigonocerataceae derived directly or indirectly from Oncocerida; origin of Clydonautilaceae and Aipocerataceae uncertain, probably from Rutoceratidae. Nautilidae stem from Syringonautilidae.]” Dzik (1984: 149) also gave a short diagnosis: “Exogastrically coiled, moderately elongated shell with narrow, originally subcentral siphuncle (but ventral in Cenoceras, and dorsal in Aturia); larval development with an egg capsule, without planktonic larval stage.”