Fig. 10

Metamorphosis in Schizocardium californicum. Light DIC micrographs of live individuals. Anterior to the top and ventral to the left. a Larva at onset of metamorphosis, showing enlarged coelomic cavities. b-c Larvae between 3 h and 5 h after onset of metamorphosis, showing thickening of the ectoderm, posterior retraction of the pharynx, and further enlargement of coelomic cavities. d Larva around 10–12 h after onset of metamorphosis, showing almost fully formed proboscis, thickening collar, and folding of the gut. e Larva around 24 h after onset of metamorphosis, showing fully formed proboscis and collar, further folding of the gut, enlargement of pharynx and gill slits, and formation of the trunk. f Post-metamorphic juvenile, 48 h after onset of metamorphosis, showing fully formed proboscis and collar, and elongating trunk. g Close-up ventral view of the forming proboscis. Same individual as c. The anterior ciliary grooves are disappearing as the loops of the circumoral ciliary band begin to fuse. h-j Changes in coelomic organization during metamorphosis. h Onset of metamorphosis. Same individual as a. i 5 h after onset of metamorphosis. j 12 h after onset of metamorphosis. The metacoels are forming the longitudinal muscles of the trunk. k-m Changes in pharyngeal morphology during metamorphosis. k Same individual as a, showing 6 gill slits at onset of metamorphosis, and the presence of tongue bars. l pharynx at 12 h after onset of metamorphosis, showing relative position with the mesocoels. m Pharynx of larva around 24 h after onset of metamorphosis, showing addition of a seventh pair of gill slits. n-o Ectodermal gill pore formation. n Same individual as c. o Same individual as e. ao, apical organ; c, collar; gb, gill bars; gp, gill pores; i, intestine; lm, longitudinal trunk muscle; m, mouth; mes, mesocoel; met, metacoel; of, oral field; p, protocoel; ph, pharynx; post, postoral loop of the circumoral ciliary band; pr, proboscis; pre, preoral loop of the circumoral ciliary band; prf, preoral field; pvl, primary ventral lobe; s, stomach; t, telotroch; tb, tongue bar; tr, trunk. White arrows mark the posterior boundary of forming collar. Scale bars: 500 μm (a-j, l-n), 250 μm (k, o)