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 6 million years.

[1] Semiannuloceras was named by Evans (2005).

Its type is Semiannuloceras abbeyense.

[2] 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.