Figure 3

Graphic representation based on 3D-reconstructions of larval myogenesis in Lyrodus pedicellatus . Anterior is upwards in all aspects. A, C, E, G is in a lateral view and ventral is to the left. B, D, F, H is in dorsal view. (A) Earliest veliger stage investigated with oval-shaped valves and velum with a delicate velum muscle ring. Ventral and dorsal velum retractors extend into the velum. Ventral larval retractors project ventrally. The anterior adductor muscle has contact to the dorsal velum retractor. (B) Earliest veliger stage investigated showing the two portions of the anterior adductor muscle which spans between the left and right valve. Paired velum retractors project into the velum. (C) Early veliger larva with the anlage of the foot retractors that originate at the paired ventral velum retractors, which now consist of two distinct bundles. Note that the ventral larval retractor has already disintegrated in this early stage. (D) Early veliger larva with the developing foot retractors which project towards the midline. (E) Slightly further developed veliger showing two intercrossing bundles of the ventral velum retractors. (F) Veliger with the left and right foot retractor that meet in the midline and fuse. (G) Developing median muscle fibres that form the anlage of the pedal plexus in the mid-veliger larva. An oral velum musculature appears. On both sides, the two branches of the ventral velum retractor fuse. Note that the accessory velum retractor is attached to the outer surface of the anterior adductor muscle. (H) Mid-veliger with unpaired accessory velum retractor.