However, despite containing relatively few cell types and lacking elaborate organ structures, the medusa have much greater anatomical complexity than their polyp form. Adult medusa are on average 1 cm in diameter. They are almost entirely transparent, their gonads, radial canals, short stomach, and four-lipped mouth being their most clearly visible anatomical structures. Each medusa has four gonads positioned midway along each endodermal radial canal. The gonads themselves are transparent, allowing for visualization of the oocytes within. Each medusa typically has around 32 tentacles, each of which are covered in stinging nematocyte cells. These nematocytes are considered specialized nerve cells despite the fact that they are composed of a pressurized capsule (nematocyst), a rapid-firing, harpoon-like dart and lethal toxins made for killing prey. "Clytia"’s nervous system is well-organized and highly specialized. Two parallel condensed nerve rings run around the periphery of the medusa’s bell; the outer rings is responsible for integrating sensory inputs, while the inner ring coordinates motor responses. Specialized balance organs known as statocysts are also located between tentacles. Medusa also have both smooth and striated muscle that allows for the contractions necessary to swim smoothly through the water. Since "C. hemisphaerica" passes through planula, polyp, and medusa stages during its life cycle, it is regarded as a good model for studying how one genome can produce variable phenotypes. This is especially useful when considering that two of the more common Cnidarian model organisms, "Hydra" and "Nematostella", do not have the same “complete’ life-cycle that alternates between a vegetative polyp and sexually reproducing, free-swimming medusa form. "Clytia" has characteristics that make it favorable for laboratory culture and experimental manipulation. All stages of "Clytia"’s life cycle can be reproduced under laboratory conditions; polyp colonies, due to their essentially immortal nature, are easily maintained, and adult medusa can be fed with "Artemia" larvae. Adult male and female medusa spawn daily, and can be entrained with controlled light conditions to spawn at specific times. The oocytes, eggs, embryos, and planulae of "Clytia" are easily visualized under a microscope and, much like those of popular model organisms like sea urchins, the zygotes of "C. hemisphaerica" are relatively large (around 200 um in diameter) and can be microinjected to form transgenic planulae, polyp colonies, and medusa.