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(invertebrate zoology)
A primitive order of tetrabranchiate cephalopods; shells are external and smooth, being straight or coiled and chambered with curved transverse septa.



a superorder of invertebrates of the class Cephalopoda. The nautiloids appeared in the Cambrian and reached their zenith in the Ordovician and Devonian; they became rare in the Mesozoic and Paleocene. Modern representatives of the nautiloids constitute the single genus Argonauta.

The shell structure of nautiloids is similar to that of the ammonites. The nautiloids, however, have simpler septa to divide the shell into chambers and a siphon that, as a rule, is not situated along the shell wall. The structure of the initial parts of the shell in nautiloids differs from that in ammonites.

The extinct nautiloids made up approximately 700 genera, embracing more than 2,000 species. These predators lived in the sea; their modes of locomotion included creeping, soaring, and swimming.

The Nautiloidea are important in the study of the development of the Cephalopoda and in the stratigraphy of lower Paleozoic deposits.


Osnovy paleontologii: Molliuski-golovonogie, part 1. Moscow, 1962.


References in periodicals archive ?
Because fossil nautiloids are common in Ontario's fossil record, the ROM tried for about a year to keep a living nautilus.
The young of ancestral nautiloids, Wells says, "could not possibly have adopted the [modern] nautilus lifestyle.
The nautiloid cephalopod Cymatoceras hilli (Shattuck, 1903) from the Cretaceous (Albian) Walnut Formation, central Texas.
Colour pattern polymorphism in Silurian nautiloid Phragmoceras Broderip, 1839.
5 + m--microlaminated, silty, argillaceous eurypterid-dolostone with Eurypterus remains, nautiloids, and ostracods (Herrmannina).
Theoretical approaches have been applied to fossil nautiloids (e.
At the age of ten, I can remember hiking to those rocky cliffs and collecting fossils of nautiloids and brachiopods.
In another example, Signor and Brett (1984) described the marked increase in sculpture among gastropods, brachiopods, nautiloids and crinoids, paralleled by the subsequent decline of clades without these features.
Manda and Turek discuss colour ornamentation in straight-shelled nautiloids in the Ordovician and Silurian, and Szaniawski describes Early Palaeozoic conodont-like fossils of uncertain affinity.
Other macrofossils present, or locally characteristic, within this formation are orbitolinids, nautiloids, brachiopods, vermetid gastropods, solitary corals, serpulids, echinoids, Plicatula placunea and Lithocodium aggregatum (e.