The siphuncle is located halfway between the shell axis and the venter, is thin walled and tubular with short, orthochoanitic septal necks and segments that are only slightly inflated.

The adult, or mature ascoceroid conch, as it is referred to, typically consists of an expanded exogastric brevicone with unique features.

The Ascocerida are derived from the michelinocerid family Clinocertidae[2] in the early Middle Ordovician, possibly from Clinoceras through such slender forms as Montyoceras and Hebetoceras.

The connection between these slender deciduous forms and the typically ascoceroid Probillingsites from the early Upper Ordovician can be made through the slightly inflated Redpathoceras.

The Choanoceratidae is established for the derived Upper Silurian Choanoceras, characterized by septa that form deep symmetrical cones[1] and a subcentral expanded siphuncle with cyrtochoanitic and recumbent septal necks at maturity.