LATE DEVELOPMENT OF THE PAN-NEOTROPICAL NEREIS-RIISEI GRUBE, 1857 (POLYCHAETA, NEREIDIDAE)

Development of Nereis riisei Grube, 1857, a pan-neotropical nereid pol ychaete, is described based on a collection from the type locality, St . Croix, U.S. Virgin islands. Specimens range in size from 13 to 68 se tigers, too small for dissection and so were mounted in a clearing med ium. A type of seta unique to the species was present in all specimens but paragnaths were not present until 24 setigers. As the worms matur e, there is an increase in overall size and in the number of setigers, paragnaths, jaw teeth, and setae. Utilization of this information per mits identification of small specimens. The late development of this s pecies is compared with that of other nereids.