Life Cycle of the Sea Cucumber

Sea cucumbers belong to a classification of animals known as echinoderms. This group of animals exists solely in salt water and includes such animals as the sea star, or starfish, sea urchins, and brittle stars. They are the most complex invertebrates, but are still simple organisms that do not have a brain or other sensory organs and are characterized by their remarkable radial symmetry and unique water vascular system.

  1. Asexual Reproduction

    • Sea cucumbers can reproduce both sexually and asexually, though most species have defined sexes. During asexual reproduction, the sea cucumber will divide itself down the median line, also known as fission, to create two separate organisms, which will complete their development by regenerating the missing body parts. Some can only complete this process if certain parts are present.

    Sexual Reproduction

    • External reproduction involves the external fertilization of eggs by releasing sperm into the water. The fertilized eggs will hatch and the larvae will live a planktonic, or free floating existence, swimming along with the aid of tiny cilia for mobility, eating and growing until they have reached the metamorphosis milestone.

    Metamorphosis

    • Sea cucumbers undergo a metamorphic phase, where they transform from the larval stage into adults. During the metamorphic phase, the larvae will experience a complex organization and degeneration of internal structures. After emerging from the metamorphic state, the newly formed adults will continue to grow and develop until they take on the familiar radial symmetry of more mature adults.

    Development

    • The newly emerged adults sink to the bottom in order to complete their development. They are now in their adult form, but will continue to grow until they reach their adult size. After they reach their full adult size and the lifecycle begins again.

    Unique Characteristics

    • Sea cucumbers have a unique defense mechanism. When threatened, they can squirt water through its water vascular system. This makes them shorter, fatter and harder to grab. Sometimes this reaction is so violent that the sea cucumber actually expels its internal organs. The good news is for the sea cucumber is that it can regenerate all its organs within a few weeks.