Figure 9

Confocal micrographs of the myogenesis in premetamorphic and metamorphic developmental stages of Aeolidiella stephanieae. Anterior faces upwards and scale bars represent 50 μm in all aspects. All aspects are in lateral view except A which is in dorsal view. (A) Early veliger larva showing first fibres of the larval retractor muscle (lrm), the accessory retractor muscle (arm) and the velar ring muscles (vrm); v marks the velum. (B) Slightly later stage as in A with a more elaborated musculature than in A, and the first fibres of the pedal musculature (pm). (C) The musculature in a veliger consists of retractor muscles, velar ring muscles, pedal muscles, as well as thick metapodial retractor muscles (mrm); mp marks metapodium. (D) Slightly older veliger larva with more elaborate musculature than in C, the retractor muscles are more dominant, the pedal branch of the larval retractor muscle fuses with the metapodial retractor muscle to a thick muscle layer close to the operculum (o). (E) Slightly later stage as in D with a strong larval retractor muscle running to the margin of the velar ring muscle and to the larval foot. (F) In the late veliger stage the most prominent muscle is the larval retractor muscle, and it seems to be fused with the accessory retractor as well as metapodial retractor muscle; pp marks propodium. (G) Larva at the beginning of metamorphosis the velar musculature is degenerating (open triangles). (H) Slightly later stage as in G showing the ongoing degeneration of the larval retractor muscle as well as the velar muscles.