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

Four main types of radula are found within the gastropod superfamily Conoid ea. Type 1, the Clavidae type has five teeth in each row with comb-like lat erals and flat pointed marginals. Type 2, the Turridae type has two or thre e teeth in a row with the marginals comprised of teeth with the duplex or w ishbone form. Type 3, the Pseudomelatomidae/Pervicaciinae type has two or t hree teeth in a row with the marginals curved and solid. Type 4, the hypode rmic type has two hollow, enrolled, marginal teeth in each row with the rad ular membrane reduced or absent. Study of the maturing teeth along the radu lar membrane in gastropods with the Type 2 radula shows that the duplex tee th 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 an d Toxiclionella develop in a similar way. In Conidae where a vestigial radu lar membrane is attached only at the base of the teeth, the teeth are enrol led from first formation in the radular sac. This study demonstrates that d uplex and enrolled teeth develop by a similar process, allowing the possibi lity of deriving hypodermic teeth from duplex clades as has been suggested by previous phylogenetic analysis.