Fig. 2: C. magus life history and venom apparatus morphogenesis.

Morphogenesis of the venom apparatus was initiated early during larval development and its components elaborated from the distal oesophagus (foregut). a The oesophagus of hatching larvae consisted of a simple tube of ciliated epithelium, with the prospective buccal cavity and radular sac rising from a patch of enlarged cells embedded in the ventral wall of the oesophagus (see Supplementary Fig. 1a, b). Black arrowhead indicates position of the mouth. b In late larvae, the buccal cavity and radular sac could be seen as interconnected chambers beneath the oesophagus (see Supplementary Fig. 1c). The prospective venom gland was evident as an accumulation of secretory cells in the ventral wall of the oesophagus, posterior to the buccal cavity (see Supplementary Fig. 1d). c The onset of metamorphosis was marked by the resorption of the velum and loss of the larval mouth and anterior oesophagus (see Supplementary Fig. 1e). d At 2 dps, the buccal tube had formed and chitinous radular teeth started accumulating in the radular sac (see Supplementary Fig. 1f). e By 6 dps, the venom gland had pinched-off from the oesophagus, remaining only connected to the buccal cavity, and its distal end became encapsulated with the venom bulb. dph days post-hatching, dps days post-settlement.