Yanhecerida

The Yanhecerida is an order of primitive nautiloid cephalopods from China, confined to the late upper Cambrian Wanwankou member of the Fengshan Formation. Their most probable origin is from the plectronocerid genus Plectronoceras.

Yanhecerid siphuncles are ventro-marginal, with strongly curved diaphragms that are convex toward the apex and concave toward the front of the shell.

The Yanhecerida includes a single family, the Yanheceratidae with four genera -- Yanheceras, Aetholoxoceras, Achendoceras, and Oonendoceras. The shell of Yanheceras is an endogastric cyrtocone. Those of Aetholoxoceras, Achendoceras, and Oonendoceras are generally orthoconic; their siphuncle interiors differing in complexity.