Life Cycle of the Aurita
Moon jellies are among the most commonly known of the medusan jelly fish. Aurelia aurita is the moon jelly native to the Pacific Coast of North America. This species has been well studied, and is a common exhibit in both professional aquariums and in amateur aquarium hobbyist's collections. As a result the life cycle is well documented, though fairly complex.
Moon Jelly Basics
Moon jellies are denizens of shallow coastal waters. Their lives and life cycle are dependent on shallow water environment. Seldom found in deep waters, moon jellies of various species are common throughout the temperate and tropical oceans of the world.The species are predatory, and under the wrong conditions can easily overrun a fragile ecology.
The body of a jelly fish is shaped like a common grocery store mushroom. The upper umbrella contains the stomachs and gonads, and is fringed with tentacles and mild stinging threads. The stem carries a secondary ring of tentacles that resemble the "collar" on the stem of a ripe and opened mushroom. The stem then continues down into a set of arms that feed the central mouth leading up the stem. The stem also contains a canal leading down the arms and up into the body called the manubrium canal.
Sexual and Asexual Reproduction.
Aurelia Moon Jellies are capable of both sexual and asexual reproduction. In their medusan form, (the form commonly understood as a jelly fish) , they reproduce sexually. Males have long strings of sperm flowing among the central body tentacles. Females have egg clusters embedded in the manubrium canal.
The asexual reproductive period occurs in a second stage called the polyp. Where the moon jelly medusa is free swimming in the ocean; the polyp is an organism rooted to the sea floor or to a convenient rock, stone, or other anchor point. Where medusan adults generate offspring through the combination of egg and sperm, polyps produce offspring through cell division and fission of clone offspring.
Polyps, both those generated by sexual production and those cloned by asexual generation can in time give rise to a new medusan through a process called strobilation, which is not entirely unlike the creation of new polyps but it takes a different branching as it grows.
Described in excruciating detail, the truth is slightly more complex than this. Both forms in certain species and subspecies able to perform both sexual and asexual reproduction. But the rule of thumb is that the medusa has sexual reproduction, the polyp asexual reproduction, and the polyp generally gives rise to both new polyps and new medusae will carry you through the most common pattern.
Eggs, Sperm and Larva.
Moon jellies congregate in large masses, ensuring higher odds of fertilization when they broadcast their sperm and eggs. The sperm and eggs meet and form a larva. The larva is mobile: a single celled animacule with cilia. The larva is an opportunistic feeder devouring single celled organisms and plankton until it comes to rest in a place it can anchor.
Polyp.
On anchoring to a surface the former larva becomes a polyp. Polyps resemble a sea anemone, or tiny feather duster. They are attached at the base, rise up on a long stem, and are topped with an array of tentacles that can capture passing organisms and stuff them into the central mouth at the top of the polyp.
The polyp will ultimately form feathery sections, each stacked above the next, nesting in a long, fringed column. At the time of reproduction a layer will begin to individuate, developing its own contained physical system. Though genetically identical to the polyp it is becoming its own individual self--a self that will form into a moon jelly genetically identical to the parent polyp, but with the genetics expressed as a moon jelly fish.
Imagining The Cycle.
This basic cycle, from medusan jelly fish form to larva, to rooted polyp to free floating juvenile jelly fish again, is an accurate rough estimate of the true cycle of the moon jelly. It is important to realize, however, that there continue to be variants. Both "adult" forms, the moon jelly form and the polyp, are capable of functioning in both sexual and asexual modes. They each have one characteristic mode most likely to be used, but the secondary ability in each functions as a form of backup, making the moon jelly a highly adaptable organism. Its capacity to reproduce in whatever way is available is a major optimization of method.
Drawbacks.
The primary drawback to this adaptability is that moon jellies can over reproduce, overloading an ecosystem. Moon jellies are carnivorous predators devouring tiny prey ranging from protozan forms to fish eggs and fry. Therefore a surge in moon jelly population can wipe out entire sections of their own biome and cause rapid crashes in other non-prey life forms dependent on the same or closely affiliated life forms.
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