The Choanoceratidae is a small, mono-generic, family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of extinct nautiloid cephalopods in the order Orthocerida

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda 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...

 that lived in what would be Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 during the middle Silurian

Silurian

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 from
428.2—426.2 mya, existing for approximately .

Taxonomy

Chaonoceratidae was named as the family for its sole member Choanoceras by Miller (1932) who, along with Flower (1941) regarded it is belonging to the Ascocerida

Ascocerida

The Ascocerida are comparatively small, bizarre nautiloids known only from Ordovician and Silurian sediments in Europe and North America, uniquely characterized by a deciduous conch consisting of a longiconic juvenile portion and an inflated breviconic adult portion that separate sometime in...

. It became impossible to trace Choanoceras to the ascocerid lineage however and based on closer affinities was assigned to the Michelinoceratida (Orthocerida equivalent) by Flower (1962).

Morphology

Choanoceras had a slender, very gently curved shell with a natural truncation where it discarded the apical portion sometime during its life, somewhat resembling earlier ascocerids, and siphuncle segments that became gradually more expanded during growth. Nothing is known of the animal itself.