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Reproduction

Sexual reproduction
All ascidians are hermaphrodite. However, the position, number and constitution of the gonads varies in the different orders. In general, in the Enterogona, the gonad lies either within or alongside the loop of the intestine, while in the Pleurogona the gonads are associated with the mantle wall (Enterogona gonads, Pleurogona gonads).

Enterogona
Among the Enterogona the gonad remains single and a long conducting system with oviduct and sperm duct enables the transport of sexual products.

Pleurogona
In the Pleurogona, one end of the gonad is always in the proximity of the atrial siphon and a single conducting system no longer has any particular merit; ducts open independently into the atrial cavity and the massive gonad tends to split into smaller units. In some families the gonad have become single on both sides (Molgulidae), but in others it is present as several elongate units (Styelidae and Pyuridae), or even as numerous small units, known as polycarps (genus Polycarpa).

Viviparity
Viviparity appears in members of some families. In these species, the size of the eggs increases and a shortening or reorientation of the oviduct takes place.

Larvae
Peculiar to the ascidians is the tadpole larva. This larva is best developed in colonial species of the order Enterogona. It is approximately I mm long and consists of a trunk and a slender muscular tail, both covered with a test, which is further developed as a flattened fin around the tail (ascidian larva). At its anterior end, the trunk bears mostly three papillae, which are adhesive organs used for the larval settlement. The trunk houses the anterior part of the central nervous system, the cerebral vesicle. The remaining part of the nervous system extends within the tail, dorsal to the notochord.
The larva does not feed and its functions are dispersal and the choice of site for settlement. It may swim for only a few minutes or for many hours before fixing and metamorphosing to the adult form.
In the other families of the order Enterogona and in the order Pleurogona, due to reductions, not all features are as clear as described above.

Asexual reproduction
Regeneration and asexual reproduction are highly developed in colonial tunicates, but totally absent in some other families. Asexual reproduction takes place by means of budding and is specific for the different families. The resulting zooids remain in association to constitute the colony.