miR-184 expression during B. lanceolatum and B. floridae development. Anterior to the left and dorsal up in D, E, F, I, J. Scale bars are 50 μm for whole mounts and 25 μm for cross sections. A-D, K-N: 2-cell stage, 16-cell stage (B, viewed from the vegetative pole; L, side view), blastula stage (3.5 h post fertilization), cup-shaped gastrula (side views, 6 h and 7 h post fertilization in D and N, respectively). O: Dorsal view of early neurula with anterior toward left. E, P: Side view of mid-neurula. F: Side view of late neurula. Expression was found in the cerebral vesicle, somites and in the primordium of first gill slit (arrow). G, H: Cross sections through levels g and h in F showing expression in cells of the cerebral vesicle (arrow) and in somites (arrowheads). I: Side view of a first gill slit larva. Q: Side view of a two gill slit larva. J, R: Higher magnifications of anterior region of the specimen in I and R respectively showing expression in the cerebral vesicle (cv), preoral pit (arrowhead), endostyle (e) and club shaped gland (cg) (arrow).