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Scyphozoans

Reproduction & Development

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Scyphozoa exhibit both sexual (medusa) and asexual (polyp) reproduction.  While both forms are present, the medusa (sexual) form predominates.  Sexual reproduction is not internal.  Males release sperm, and females release eggs into the water.  This is where the sperm and egg fuse.  The larva, known as a planula, is a free swimming organism covered in cilia.  It swims around and attaches itself to a hard substrate, such as a rock.  Here it metamorphoses into a polyp (scyphistoma) form. The scyphistoma has a similar appearance to a hydra it is cup shaped with tentacles surrounding a single opening.  The scyphistoma will reproduce asexually via budding into stroblia.  The stroblia live in a colony compounded on top of one another.  Each stroblia matures into a ephryae.  An ephryae is an immature from of a medusa.  As they mature they break away from the other stroblia, and mature into adult medusas, which reproduce sexually. Mature medusas are dioecious, which means that each one is either male or female. This polyp/medusa life cycle is known as alternation of generations.  The scyphozoan alternates between sexual and asexual reproduction.  This results in the alternation of polyp and medusa generations.  However as mentioned before the medusa stage predominates. 

There is one little exception to the normal reproductive habits of scyphozoa.  Aurelia, the moon jelly,  the eggs become lodged in pits on the oral arms, which form a temporary brood chamber where fertilization takes place.  Once the planula is released it goes through the same lifecycle as listed above.

 

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The Lifecycle of Scyphozoa

The Lifecycle of Scyphozoa

Egg -> Planula -> Scyphistoma -> Stroblia -> Ephyrae -> Adult Medusa

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