Student Project Figures Figure 14 A schematic diagram showing the settlement and metamorphosis of an ascidian tadpole larva. (a) The tadpole larva attaches to the substratum. (b) The post-anal tail regresses and features unique to the larval stage disappear. (c) The body axis rotates, culminating in the internal configuration seen in most adult zooids. (d) The stigmata increase in number and the filter feeding apparatus is established. The juvenile zooid seen in (d) is referred to as an oozooid and subsequent buds are blastozooids. Note that the zooid in the diagram possesses an atrial siphon, which is replaced by a wide atrial opening in Botrylloides spp. The tadpole can reach a length of 3 mm and the oozooid is approximately 2 mm in length. Diagram adapted from Ruppert et al., 2004.  Figure 14