Helianthoides, commonly known as sunflower starfish, begin their life cycle

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].

Starfish

Sun flower Sea Star, Phylum Echinodermata in North...

Starfish

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

Echinoderm

Asterias sp., young brachiolaria larva from the si...