Epitoky, brooding, and precocial larvae in Epigamia magna (Polychaeta: Syllidae)

Abstract

Abstract: Syllidae (Polychaeta) show a remarkable variety of reproductive strategies related to their transformation into the pelagic spawning epitoke form. Syllids can create epitokes through schizogamy, where stolons bud off, or epigamy, where the entire adult transforms in order to swim, and after fertilization they often brood their young with a variety of mechanisms. Epigamia magna (Berkeley, 1923) is a large syllid in the subfamily Autolytinae, and although its reproduction and larval development are poorly known, the subfamily is known for ventral brooding. I collected two fertilized female epitokes, one unfertilized female, and one male by night-lighting in late June and recorded their development. The fertilized females exhibited a long brooding period, at least 13 days, and the larvae which emerged from the brood sac were ciliated and highly developed, already at the 4-setiger stage. They quickly developed the fifth setiger within 2 hours, and grew to be 1100 μm by hour 44. My observations of these larvae somewhat conflict with previous reports, as I found they were 800 μm long at hatching, with six red eyes. E. magna's large body size and long brooding period appear to allow heavy investment before larvae are released into the water column. I discuss a few of the many unresolved questions about this species' reproduction, including seasonal limits, the cues for swarming, and a potentially annual life cycle.