Patterns of Growth and Setal Development in the Deep-Sea Worm, Strepternos Didymopyton (Polychaeta: Chrysopetalidae)

A number of post-larval and juvenile chrysopetalid polychaetes were made available for study from experimental wooden panels collected in deep waters of the western Atlantic Ocean. Benthic post-larvae of 10 to 11 segments possess a large rounded prostomium with eye spots, two pairs of larval dorsal and ventral cirri and cilia tufts associated with sites where notopodia are developing on segment 2. Juveniles of 12 to 30 segments exhibit reduction in size of prostomium; gradual loss of eye pigment; loss of larval cirri; development of notopodia of segment 2 and subsequent torsion of neuropodia of segment 2 dorsally. Juveniles display distinctive petaloid notosetal paleae and notosetal patterns unlike the narrow, pointed paleae and notosetal patterns observed in adults. Observed setal change is linked to hypothetical life strategies of Strepternos didymopyton. Possible origins and function of paleate setal change is discussed.