Semiannuloceras is an extinct genus of actively mobile carnivorous cephalopod of the family Baltoceratidae that lived in what would be Europe during the Ordovician from 490–460 mya, existing for approximately .PaleoBiology Database: Semiannulocerase, basic info
Taxonomy Semiannuloceras was named by Evans (2005). Its type is Semiannuloceras abbeyense. It was assigned to Baltoceratidae by Evans (2005).D. H. Evans. 2005. The Lower and Middle Ordovician cephalopod faunas of England and Wales. Monograph of the Palaeontographical Society 623 :1–81
Morphology The shell is usually long, and may be straight ("orthoconic") or gently curved. In life, these animals may have been similar to the modern squid, except for the long shell.
References
Fossils (Smithsonian Handbooks) by David Ward