lies over two clefts in the pharynx, one on either side, rather than the much larger number of clefts found in most other tunicates. Furthermore, the Appendicularia retain the ancestral Chordate characteristics of having the clefts, and the anus open directly to the outside, and by the lack of the atrium and the atrial siphon found in related classes. Reproduction and genetics Larvaceans reproduce sexually. The immature animals resemble the tadpole larvae of ascidians, albeit with the addition of developing viscera. Once the trunk is fully developed, the larva undergoes "tail shift", in which the tail moves from a rearward position to a ventral orientation and twists 90° relative to the trunk. Following tail shift, the larvacean begins secretion of the first house. Fertilisation is external. During egg release the body wall ruptures, killing the animal. The recent development of techniques for expressing foreign genes in Oikopleura dioica, which unlike all other known larvaceans have separate sexes instead of being a protandric hermaphrodite, has led to the advancement of this species as a model organism for the study of gene regulation, chordate evolution, and development. References de:Copelata