Life Cycle of a Typical Star

Starfish belong to a group of animals known as echinoderms. While starfish are simple organisms as they lack brains and other sensory organs, they are the most complex invertebrates known. Starfish have several defining characteristics. The one most noticeable is its radial symmetry. The starfish can be cut in half from any direction and end up with two equal pieces. This is especially helpful during asexual reproduction.

  1. Sexual Reproduction

    • Starfish are not hermaphroditic and have both male and female organisms. During mating, the female will release her eggs into the open ocean, where they will intermingle with the released sperm of the males. To increase their chances of success, many starfish will gather into groups when it is time to mate, coordinating their releases based on environmental and chemical factors.

    Development

    • The fertilized eggs float to the surface of the ocean, where they hatch into first stage larvae. The larvae, known at this stage as bipinnaria will do nothing but eat and grow. Second stage larvae are known as brachiolaria. Both of these stages live among the zoo plankton, eating both the yolk from their eggs and other planktonic particles. They move by using the tiny hair-like structures on either side called cilia. Both larval stages lack the radial symmetry of the adults, but are bilaterally symmetric, meaning they are the same on the left as they are on the right.

    Metamorphosis

    • After reaching a certain point in their growth, the brachiolaria are ready to enter metamorphosis. The larvae drift down to the ocean floor to complete their development, continuing to grow and move from their bilaterally symmetric shape to the more recognizable radially symmetric shape. Most sea stars have five arms, but some species have more and a few have less.

    Life Expectancy

    • The average life expectancy for a starfish in captivity is eight years, though not much is known about the lifespan of sea stars in the wild. It is estimated that most will live somewhere between five and 20 years based on species and environmental conditions.

    Asexual Reproduction

    • Though sexual reproduction is the preferred method of reproduction in echinoderms due to the increased number of offspring and genetic diversity, starfish can reproduce asexually if no mates are present. This is accomplished by a process known as fission. The starfish will actually sever an arm from its body that will eventually regenerate its missing body parts into a new organism, though this is only possible if a portion of the central disc is present.