Nautiloid

A cephalopod in the group Nautiloidea, characterized typically by an external chambered shell. Nautiloidea includes living nautiluses and many extinct forms.

Nautiloidea: A cephalopod subclass comprising nautiluses and their extinct relatives. This taxonomic group defines which animals count as nautiloids.
Nautilus shell: The coiled external shell of a nautilus, divided internally into chambers. It provides a living example of how a nautiloid shell is organized.
Paleozoic: The geologic era from about 539 to 252 million years ago. Nautiloids diversified extensively during this era.
Allonautilus: A genus of living nautiluses distinguished by distinctive soft-tissue features. It is one of the few surviving branches of nautiloid diversity.
Cephalopod: A marine mollusk with arms or tentacles and a prominent head, including octopuses, squids, cuttlefish, and nautiluses. Nautiloids are members of this broader mollusk group.
Camerae: The chambers formed behind the living body as a chambered cephalopod shell grows. These empty chambers make up most of a mature nautiloid shell.
Ordovician: The geologic period from about 485 to 444 million years ago. Some of the earliest known nautiloids appear in Ordovician rocks.
Chambered nautilus: A living nautilus species, Nautilus pompilius, with a spirally coiled chambered shell. This species is a widely recognized living representative of nautiloids.
Nautilus: A living cephalopod genus with a coiled, chambered external shell. Its living species show the familiar nautiloid shell form.
Nacre: A layered form of aragonite and organic material lining some mollusk shells. Nacre forms part of the inner shell layers in living nautiluses.

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MonoplacophoraCompared with: Their resemblance to some fossil monoplacophorans once complicated interpretation of the fossil record.