Fig. 2

Early metatrochophores of Siboglinum fiordicum, by SEM (A, B) and phalloidin staining and CLSM (C–H). A, B Ventral and dorsal view of the larva in that the first septum (sI) internally divides body into two tagmata: common anterior segment and common opisthosomal segment. Dorsal side distinguished by the presence of the ciliated spot (cp) (B). C Dorsal view of the larva, distinguished by the presence of the single dorsal longitudinal muscle strand (md) and asymmetric tentacular muscles (tm). D, E Left lateral view distinguished by the presence of the ventrolateral longitudinal muscle strands (mvvl, mlvl) and layer of circular muscles in the anterior part of the body. Circular muscles encircle the body and overlap on the ventral (D’) side of the body. F–H Ventral, lateral, dorsal views of the opisthosoma bearing three first circular bands (moc1-3). ca—annular chaetae, co—opisthosomal chaetae, cp—dorsal ciliated spot, m—mesotroch, mc—circular musculature, mca—muscles of annular chaetae, mcch1-3—circular muscles of the chaetal apparatus, md—dorsal longitudinal muscle strand, mlch—longitudinal muscles of the chaetal apparatus, mls—longitudinal muscle of the first septum, mlvl—lateral component of the ventrolateral longitudinal muscle strand, moc1-3—circular muscles in the opisthosoma, mrtg—radial muscles interconnecting mtg and longitudinal muscle strands, mtg—muscles of the tubiparous glands, mv—ventral longitudinal muscle strand, mvvl—ventral component of the ventrolateral longitudinal muscle strand, na—anterior neurotroch, np—posterior neurotroch, p—prototroch, sI—place of the first septum, tm—muscle bundles of the tentacular anlage