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Fig. 3 | Frontiers in Zoology

Fig. 3

From: Myogenesis of Siboglinum fiordicum sheds light on body regionalisation in beard worms (Siboglinidae, Annelida)

Fig. 3

Late metatrochophores of Siboglinum fiordicum, by SEM (A) and phalloidin staining and CLSM (B-F). A Lateral view of the larva with the visible first septum dividing common anterior segment (fr + tr) from the segmented opisthosoma (o1, o2-6), it has opisthosomal chaetae (co) and bud of future tentacle (tb) which are also shown in (A’). B–D Lateral, dorsal and ventral views of the late metatrochophores with well-developed longitudinal and circular musculature. At this stage, the muscles of the first septa remarkably increase, six circular bands marking position of the opisthosomal septa are formed, the musculature of the first opisthosomal chaetae is formed. E, F Ventral and lateral view of the larvae showing muscle contractions during movement. Late metatrochophores with holes in the ventral strand (F’) which is a reminiscence of the mouth which was open and functional in the ancestors (shown by*). aff—frontal fold, ca—annular chaetae, co—opisthosomal chaetae, cp—dorsal ciliated spot, f—frenulum, fr + tr—common anterior segment, m—mesotroch, mc—circular musculature, mca—muscles of annular chaetae, mcc—lateral circular muscle fibers interconnecting the longitudinal strands, md—dorsal longitudinal muscle strand, md1-2—two components of md in the postannular trunk segment, mlch—longitudinal muscles of the chaetal apparatus, mls—longitudinal muscle of the first septum, mlvl—lateral component of the ventrolateral longitudinal muscle strand, mlvl1-2—two components of mlvl in the postannular trunk segment, moc1-6—circular muscles in the opisthosoma, mtg—muscles of the tubiparous glands, mv—ventral longitudinal muscle strand, mvvl—ventral component of the ventrolateral longitudinal muscle strand, mvvl1-3—three components of mvvl in the postannular trunk segment, na—anterior neurotroch, np—posterior neurotroch, p—prototroch, pe—peristomium, pr—prostomium, sI—the first septum in the larval ontogenesis, sII—the second septum in order of formation, tb—tentacular anlage, tm—muscle bundles of the tb

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