epitokes

Epitokes are reproductive forms of certain polychaete annelids produced by a process called epitoky. In an epitokous transformation, an atoke—the non-reproductive individual—develops specialized, gamete-bearing segments and often assumes a streamlined, pelagic form. Epitokes are typically free-swimming and sexually mature, adapted for dispersal and external fertilization, while the atoke remains benthic and feeding.

In many polychaete species, most notably the palolo worms (for example Palola viridis) and related taxa, epitokes detach from the parent worm and migrate toward the surface to release eggs and sperm in synchronized spawning events. Spawning is frequently timed with environmental cues such as lunar cycles. Fertilization is usually external, and after spawning the epitokes die; the atoke may survive to reproduce in another season in some species.

Morphologically, epitokes differ from atokes by a development of swollen, gamete-rich posterior segments, which may be opaque or pigmented and are often adapted for rapid swimming and swarming behavior. The transformation is a temporary reproductive stage, specific to the life cycle of the species, and is not a separate taxonomic entity.

Ecologically, epitoky and mass spawning create substantial pulses of nutrients and prey for surface-dwelling predators and are a notable example of metamorphosis among annelids. The term epitoke derives from Greek, meaning “upon birth.”