Fascinating Information About The Starfish Life Cycle
Many people have probably never given much thought to a starfish life cycle but they are exceptionally fascinating creatures. They belong to the phylum echinoderm family that contains over an astonishing 6,000 different species. This Greek name that means “spiny skin” is given to this family that exists only in the sea and includes sea stars, brittle stars, sea cucumbers and urchins. Starfish are incredibly simple animals that lack any complex sensory organs or a brain, yet they still eat, move, sleep and kill their prey. They are primarily known for three features being their water vascular system, internal skeleton and radial symmetry.
The radial symmetry of a starfish is perhaps its most striking feature. Its body is equally divided into five appendages that point outward. However, it is interesting to note that the larvae typically has bilateral symmetry and changes its body shape during maturity while settled down on the floor of the sea. Their water vascular system is remarkably unique as well. There is a phenomenal hydraulic network of canals that runs throughout the body and then they all end in the form of tube feet. If you examine the ventral side of the body, you will literally see hundreds of tube feet all formed neatly in a row. By controlling its internal water pressure, the starfish can contract and extend their tube feet for respiration, locomotion and food collection purposes. Its internal skeleton is also quite interesting, all covered with skin and spines. The skeleton consists of an abundance of calcareous plates that are called ossicles that move and form very flexible joints.
Starfish Feeding Habits
Since starfish are carnivorous and spend their days scavenging the floor of the ocean, some species literally extend their stomachs to go into their victims to digest them. They traditionally eat crustaceans, worms and bivalves. To see one eat is quite unbelievable. They will position themselves on top of their prey and then push their stomachs out through their mouths and into their victim. Their special digestive juice liquidates the prey and the cilia transports the food back into the body of the starfish for consumption.
Starfish Life Cycle And Reproduction
Examining a starfish life cycle shows how unbelievably advanced these invertebrates really are. Most species of echinoderms are considered diecious, which simply means there are distinct female and male individuals. Although reproduction in this family of creatures is sexual and involves eggs being fertilized by sperm, some species such as the starfish, are also capable of reproducing asexually.
Asexual reproduction involves two or more body parts to divide, called fission. Then the reproduction of the body part takes place. Regeneration and sexual fission require both a body wall to be torn and also the ability to seal the wound. Sexual regeneration does also require that the lost pieces contain specific body parts such as a piece of the central disk.
Sexual reproduction in the starfish life cycle involves fertilizing the eggs externally. These fertilized eggs then develop into plankton larvae that generally goes through two different stages known as bipinnaria and brachiolaria. The larvae are bilaterally symmetrical and they have cilia bands that are used to swim and eat. As the larvae slowly turns into an adult, an extremely complex degeneration and reorganization of the internal organs occurs. The right side of the larvae transitions into the aboral surface that faces upward while the left side becomes the oral surface that faces downward. The larvae then settles to the floor of the sea to finish the starfish life cycle and adopt their distinctive radial symmetry that the adults are so well known for.