See text Rayonnoceras is a genus of extinct cephalopods that lived around 325 million years ago during the Carboniferous.

[3] The endosiphuncular canal system is well developed and most chambers are filled with organic deposits.

As with earlier actinocerids, Rayonnoceras has a canal system within the siphuncle that includes a narrow opening, the parispatium, between the internal deposits and inner wall of the connecting ring.

In life Rayonnoceras was probably a bottom dweller that spent most of its time stationary, waiting in ambush for prey.

It is believed to be the largest of its kind ever found and is housed at the University of Arkansas Museum.