The giant orthocone's living tissue was at one end of a very long conical shell. It had no fins and no tail. Along the underside of the cone ran a flexible, fleshy tube. The orthocone moved along by forcing water out in the opposite direction to where it wanted to go. It controlled its vertical position by adjusting the amount of seawater in the chambers of its shell. Its mouth and metre-long tentacles emerged from one end of the shell.
It ate fish as well as arthropods, eg sea scorpions. It seized its prey using its tentacles and beak-like mouth to rip apart.