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Figure 6 | Frontiers in Zoology

Figure 6

From: Developmental dynamics of myogenesis in the shipworm Lyrodus pedicellatus (Mollusca: Bivalvia)

Figure 6

Schematic representations of myogenesis from the early veliger to the early juvenile in Lyrodus pedicellatus . Anterior view, apical faces the viewer and dorsal is upwards in all aspects. Folds of the velum are displayed by grey lines. (A) Very early veliger with paired dorsal and ventral velum retractors. Note that the paired ventral larval retractor only exists in this early stage. The anterior adductor muscle spans between the valves. (B) Early veliger showing paired anlagen of the foot retractor as a first component of the foot musculature. (C) Marginally older veliger with fused left and right foot retractors in the middle. (D) Mid-veliger with median muscle fibres in the longitudinal projection of the foot retractor. The unpaired accessory velum retractor is attached to the anterior adductor muscle. An oral velum musculature appears. (E) Late veliger larva. The median muscle fibres of the foot increase in size, manifesting as pedal plexus which is not yet in contact with the foot retractors. The posterior adductor muscle develops. (F) Mid-pediveliger with accessory adductor muscle that reaches between the valves. The pedal plexus unites with the foot retractors and together they form the foot. The paired accessory foot retractors have formed on both sides. The U-shaped mantle musculature forms and extends ventrally. The accessory velum retractor disappears. (G) Late pediveliger with reduced velum. Note the finger-shaped mantle musculature. The accessory foot retractor forms contact to the anterior adductor muscle on both sides. (H) Early juvenile. Note that the velum has been shed. Partially atrophied velum retractors have transformed into lateral and dorsal mantle muscles. Ventrally, the U-shaped mantle musculature connects to the finger-shaped mantle musculature.

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