Life Cycle of a Polychaete

Polychaeta refers to a genus of segmented worms that has approximately 9,000 known species. These worms have been found in land and marine environments, though most species are marine. These worms are sometimes known as bristle worms because of the unique chitinous projections found on each segment of their bodies.

  1. Reproduction

    • These worms reproduce sexually, and most do it externally, though not all. The reproductive organs of the female release the eggs into her body cavity, where they complete their maturation. Once the eggs reach maturity, the female will release them into the surrounding water through a small opening in her body, or by rupturing her body, which quickly results in her death. Sperm from the male worms will find the eggs and fertilize them as they float amongst the plankton.

    Development

    • The fertilized eggs will float freely among the plankton until they hatch. The larvae will eventually complete their development by adding segments. Some species do not have a larval stage, hatching smaller versions of the adult from the egg. Also, many will never feed with the exception of from the yolk sac that was contained in the egg from which they hatch.

    Epitoky

    • A few polychaeta have evolved a unique breeding technique known as epitoky. The worm will resemble most other polychaeta until breeding season. Then the worm will grow longer with new, specialized segments being added. There is an obvious division between the original worm and the newly formed sections. The front half is known as the atoke, which will not reproduce, and the rear is now known as the epitoky. Each segment of the epitoky is filled with sperm and eggs and eventually breaks off from the atoke and floats toward the surface. When the epitoky reaches the surface, the segments burst open, releasing thousand of eggs and sperm into the water to fertilize and begin the cycle over again.

    Maturation

    • Depending on the species, maturation of the larvae can take anywhere from a few days to a few weeks to complete. The average life expectancy for polychaeta is poorly understood, but some live for a few weeks, where others can live for many years.

    Special Polychaeta

    • A few special polychaeta exist. The Pompeii worm lives within the hydrothermal vents of the Pacific Ocean and are thought to be the most heat tolerant animals in the world. Another interesting polychaete is Hesiocaeca methanicola, which lives solely on the methane clathrate deposits in the ocean. And lastly, Lamellibrachia luymesi is a tube worm that regularly reaches lengths of over 3 meters. Scientists believe the worms may be the longest-lived animal at over 250 years of age.