Developmental expression of miR-124 in B. floridae (A-L) and B. lanceolatum (B-M) as analyzed by WM-LNA-ISH. Anterior is to the left and dorsal is up in all whole mounts. Cross-sections are viewed from the anterior end of animal. Scale bars are 50 μm for whole mounts and 25 μm for transverse sections. A, B. Dorsal and side views of 14 h neurulae showing expression in five spots (arrows) in the neural plate. C-E. Side views of 22 hr neurulae. D: Detail in dorsal view of the specimen in C, showing the longitudinal rows of labeled nerve cells beginning at the posterior cerebral vesicle (cv) and extending to posterior neural tube. F-I. Transverse sections through levels in E show symmetrical ventrolateral labeled nerve cells (arrows) and a single cell in the ventromedial wall of the neural tube just near the first pigment spot of the dorsal ocellus (indicated by an arrowhead). J, K: Side views of early larva. L, M: Side views of first gill slit larvae. Dark granules in the tailbud region of the late-neurula and larval stages of B. lanceolatum are pigment and not a positive reaction for miRNA transcripts.