Fig. 10

Neural development in the late mitraria larvae. CLSM images of F-actin and FMRFamide⁺ elements and Differential Interference Contrast (DIC) images showing expression of elav1 and syt1 at 4 wpf. Images are in lateral view, except for (e) which is in ventral view. Bottom row are close-up sections of the animals from the top row. a–c More FMRFamide⁺ neurons and neurites continue to form as the mitraria matures, including those innervating the foregut and the peripheral nerves of the juvenile rudiment (a), and the chaetal sac (c). See Helm et al. [14] for an extended description of the development of the FMRFamidergic and serotonergic nervous system of the late mitraria. elav1 expression has declined from the apical organ and is now restricted to the juvenile rudiment (a–c), instead, syt1 is expressed in the mature neurons of the apical organ and the juvenile rudiment. j Diagram of neurogenesis in the mitraria larvae. At 13 hpf, neurogenesis starts from anterior to posterior, with elav1⁺ and syt1⁺ cells at the apical organ and as the embryo develops, the nervous system differentiates in a ventral/posterior progression where the nerve cord of the juvenile rudiment will form. FMRFamide⁺ cells appear by 22 to 24 hpf in the apical organ and in the prototroch. an: anus; ao: apical organ; chn: chaetal sac nerve; cs: chaetal sac; dlh: dorsolateral hyposphere muscles; em: esophageal muscle; en: endoderm; fg: foregut; hg: hindgut; jr: juvenile rudiment; lfn: lower foregut nerve; mg: midgut; mo: mouth; ms: mesentoblasts; mt: metatroch; np: nephridia; pr: prototrochal ring; pt: prototroch; sn: sphincter nerve; ufn: upper foregut nerve. Scale bar is 50 µm