Formation of marginal radular teeth in Conoidea (Neogastropoda) and the evolution of the hypodermic envenomation mechanism

Abstract

AbstractFour main types of radula are found within the gastropod superfamily Conoidea. Type 1, the Clavidae type has five teeth in each row with comb‐like laterals and flat pointed marginals. Type 2, the Turridae type has two or three teeth in a row with the marginals comprised of teeth with the duplex or wishbone form. Type 3, the Pseudomelatomidae/Pervicaciinae type has two or three teeth in a row with the marginals curved and solid. Type 4, the hypodermic type has two hollow, enrolled, marginal teeth in each row with the radular membrane reduced or absent. Study of the maturing teeth along the radular membrane in gastropods with the Type 2 radula shows that the duplex teeth are not formed from two separate elements but develop from a flat plate, by thickening of the tooth edges and elevation of the posterior edge from the membrane. Semi‐enrolled and enrolled teeth of Pilsbryspira, Imaclava and Toxiclionella develop in a similar way. In Conidae where a vestigial radular membrane is attached only at the base of the teeth, the teeth are enrolled from first formation in the radular sac. This study demonstrates that duplex and enrolled teeth develop by a similar process, allowing the possibility of deriving hypodermic teeth from duplex clades as has been suggested by previous phylogenetic analysis.