Various stages of <i>N. vectensis</i> embryonic development.

<p>Development stages from egg to polyp are shown, with the oral pole to the left in panels F-H (indicated with an asterisk). A) Fertilized egg (0 h). B) Four-cell stage (3 h), often after two cleavages finish simultaneously. C) 32-cell stage (5 h). D,E) Cleavages result in a hollow sphere called a blastula (10–20 h). F) Invaginating cells at the oral pole mark the beginning of gastrulation (24 h). G) Planula larva (72 h) with a double cell layer and apical tuft (at). Black arrows indicate the oral and aboral directions. H) Juvenile polyp with four early tentacles (ten). (cd = central domain, cr = central ring, mo = mouth, oe = oral end, ph = pharynx. Development times in hours at 16°C estimated from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103341#pone.0103341-Magie1" target="_blank">[20]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103341#pone.0103341-Fritzenwanker1" target="_blank">[30]</a>.)