The Blue Sea Star- Linckia laevigata

Reproduction:

There is no sexual dimorphism in blue sea stars so the sexes appear to be very similar. The only major difference is the gonads that are present. When reproduction occurs, the sea stars gather in groups and gametes are released into the water above the animals. If males and females release gametes in close proximity, eggs are fertilized. This means that blue sea stars are polygynangrous or they mate with multiple males and females. The blue sea stars breed once a year and their gestation period is 28-30 days. They reach reproductive maturity at 2 years of age and once the gametes are released there is no parental care provided to the offspring (Baptiste and Jakimovski, 2013).

Not only do blue sea stars go through sexual reproduction but they also can go through asexual reproduction as well. This happens mostly in captivity and occurs when the starfish divide through their central disk and produce clones of themselves with the same genetic makeup.

Body Systems:

A major characteristic of the sea stars is the presence of a water vascular system. This system has fluid-filled canals derived from the hydrocoel that form during embryonic development. The canals lead to podia or tube-feet and are like tubular extensions of the water vascular system (used for respiration). The podia penetrate the body wall and skeleton in regions known as ambulacral zones and it is linked to the outside water through a plate called the madreporite. This then leads into a stone canal and then to a ring canal that forms a ring around the esophagus. Five radial canals extend from the ring canal into the arms of the sea star (Pechenik, 2015).

The tube feet on the star fish lack circular muscles so they move their limbs hydraulically. The feet retract when the longitudinal muscles contract. There is cilia located in each of the tube feet to allow the fluid to circulate throughout the water vascular system. The podia function in gas exchange, locomotion, and some excretion. There is some recent research also suggesting that tube feet are used for vision and light perception (Pechenik, 2015).

Another feature associated with the water vascular system is called the hemal system. This system is possibly thought to be used for transporting nutrients from the coelomic fluid to the gonads. The major component of the hemal system is the axial organ which may be involved in producing cells called coelomocytes. Coelomocytes are found in all tissues and body fluids and are involved in recognizing and destroying foreign material, creating pigments and collagen, transporting oxygen and nutritive material, digesting food particles and wound repair (Pechenik, 2015). The nervous system of sea stars consists of a diffused net typically of three rings centered on the mouth with radiating branches.

Sea stars also have an amazing feature where they can shed one of their limbs when they are being attacked by a predator. This is due to the fact that there is mutable connective tissue or catch tissue. Nerve impulses can alter the stiffness and fluidity of the connective tissue in the sea star and this allows for feeding, locomotion, and shedding an arm or viscera (Pechenik, 2015).

A few things that are not found in adult sea stars are a true heart, a true brain, and excretory organs.

Other Facts:

• The Blue Sea Star is the most commonly exported sea star for aquarium trade (Alcazar and Kochzius, 2015).

• This species is not included on the endangered or threatened species list!