Fig. 8
From: Early embryogenesis and organogenesis in the annelid Owenia fusiformis
Late mitraria larvae and juvenile rudiment development. CLSM images of late larval stages from a 1 wpf to h 4 wpf. a, c, e and g Are ventral views with anterior facing up, while d, f and h are lateral views with anterior facing left. b Close ups of specimens at 1 wpf. a The mature larva continues to grow and develop more musculature to connect the chaetal sac to different parts of the episphere and the hyposphere. The prototroch starts making bends (open arrowheads), and the metatroch is cleared from the chaetal sac and the ventral area where the juvenile rudiment is developing. b Both the hyposphere and episphere epithelial cells enlarge, the apical organ becomes more prominent and is full of microvilli, and the chaetal sac muscles become more robust. c–h The apical organ now is connected to the prototrochal ring via peripheral and dorsal nerves. Cyan arrowheads point to the retractor muscles. Yellow arrowheads point to esophageal and dorsal levator muscles. Red arrowheads point to branching muscle connecting the peripheral regions of the ventrolateral hyposhere and the dorsolateral hyposphere muscles. an: anus; ao: apical organ; at: apical tuft; cc: circumesophageal connectives; cs: chaetal sac; dl: dorsal levator; dn: dorsal nerve; fg: foregut; jr: juvenile rudiment; lp: lappet; mg: midgut; mo: mouth; mt: metatroch; np: nephridia; nt: neurotroch; pn1–pn3: peripheral nerves 1 to 3; pt: prototroch. Scale bar is 50 µm. In b the scale bar is 25 µm