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Pristina leidyi are tiny, delicate, segmented (annelid) worms commonly found in pond and stream sediments. They can reach high densities in the field, especially in spring and summer, owing to their ability to reproduce asexually. Asexual reproduction occurs by paratomic fission, in which a new head and tail are intercalated in the middle of the body, forming a transiently linked chain of individuals which are behaviorally and physiologically coordinated. The fission process can be completed in as little as 1 to 2 days. They have excellent regenerative abilities, being capable of regenerating every part of their body.
Pristina leidyi are largely transparent, 2 to 4 mm long, and comprised of ~15 to 35 segments. In each segment, short bristles (chaetae) protrude ventrally and long hair-like bristles protrude dorsally, the dorsal chaetae of segment 2 being characteristically much longer than the rest. These chaetae are used for both locomotory and sensory functions. At the anterior end, a thin, elongated sensory proboscis protrudes from above the mouth. These worms feed on algae and detritus. (Alexa Bely, pers. comm. August 2010)