Pristina leidyi can reproduce both sexually and asexually, although most generations are asexual.
Sexual reproduction typically occurs in the fall and involves paired mating of sexually mature hermaphrodites. Clutches of fertilized eggs are deposited in protective cocoons. Eggs undergo direct development, producing juvenile worms which crawl out from the cocoons.
Asexual reproduction occurs by paratomic fission, in which a new head and tail are intercalated in the middle of the body. By this process, the original head end of the worm acquires a new tail, and the original tail end of the worm acquires a new head, producing of chain of transiently linked individuals which eventually separate. The region of intercalated tissue is referred to as a fission zone. An individual worm can have multiple fission zones developing at once: typically, subsequently formed fission zones are placed one segment anterior to the youngest fission zone. In actively growing worms, fission zones are typically positioned between segments 15 and 18.
During paratomic fission, most organ systems maintain continuity across the fission zone and linked individuals appear physiologically and behaviorally coordinated. The ventral nerve cord, gut, longitudinal blood vessels, and longitudinal muscles all remain continuous and functional until the very final stages of fission (Zattara and Bely in press). Until worms physically separate, only the anterior-most head ingests food. Until daughter worms separate, the behavior and locomotion of the worm chain appears to be coordinated exclusively by the anterior-most head.
(Alexa Bely pers. comm. August 2010).
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