Helianthoides, commonly known as sunflower starfish, begin their life cycle when both male and females release their eggs or sperm openly into the ocean waters [a]. The starfish know when to release their sperm and egg because of an internal calendar. This makes sure both parties' have a simultaneous release time, to increase fertilization. It is then required that the egg and sperm meet and fuse to form a fertilized egg [b]. The newly fertilized egg then divides into two equal cells [c] then into four [d] and remains dividing until a hollow blastula has been formed [e]. This blastula is ciliated and hatches out of the fertilization membrane. After the first day has passed we are left with a gastrula [f]. This is a two layered stage with an inner "endoderm" and an outer "ectoderm." Since the blastula [e] stage, an indentation has been produced in the gastrula [f].
This will give rise to the future digestive system. Next the top of this new "pore" gets wider [g]. The wider portion then is pinched off and forms the "coelomic sacs" [h]. (The coelomic sacs will later become the water vascular system). Next through advancing maturity, an early bipinnaria or early larva is formed [i]. Then several portions of the early larva elongate and separate, this results in a bipinnaria [j], which swims and feeds in plankton. The bipinnaria advances further through the stages of "early brachiolaria" [k] and "late brachiolaria" [l]. Within the late brachiolaria there is a small portion called the adult rudiment. Next the late brachiolaria undergoes many changes in which it looses many parts and changes many existing parts in order to become a setting larva [m]. During this stage it usually clings onto rocks and such. The setting larva then undergoes "Metamorphosis" [see notes] where many things occur such as the old mouth being closed off and a new one made. Also the old anus is cut off and a new one protrudes. After these changes and many more we are left with an early starfish [n]. The early starfish grows tube feet and is finally able to crawl and it resembles a mature starfish. At this stage we are dealing with a Juvenile Starfish [o]. As this matures we at last have an adult starfish [p] which one day will release sperm or egg and start the life cycle over again.
Notes: o Metamorphosis is the term used to describe a form of development from egg to adult in which there is a series of distinct stages, or change of habitat.
o Some starfish have over 50 legs.
o Starfish are echinoderms and breathe through their skin.
o Some sunflower starfish grow to be over five and a half feet across.
o There are more than 1,800 types of starfish.
o They are most commonly found between Alaska and the Puget Sound.
by.... B. anderson