Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the camerae (chambers) in cephalopods, which unlike those in other orders is zoned longitudinally along the segments rather than laterally.

Evolution within the order begins with the lower Middle Ordovician Reudemannoceratidae and from there diverges into three main lineages.

[3] The Discosorida[1][2] include these families, more or less in phylogenetic sequence beginning with the oldest: These form three basin evolutionary lineages.

The first, formed by the Reudemannoceratidae, Cyrtogomphoceratidae, and Phragmoceratidae, are fundamentally endogastric with the siphuncle near the inside or longitudinally concave curvature.

In general form the Discosorida resembled the Oncocerida, which lived about the same time, but evolved from a completely different stock.