Sci230_Week_7

Physiology Assignment August 30, 2013 SCI230 Lisa Miller Jellyfish Jellyfish are sea dwelling organisms that can be very intimidating. They are extraordinary creatures that are both beautiful and mysterious. These creatures have adapted to life in the water. Jellyfish are made up more than 90% of water, which helps them float in the water (Jellyfish Adaptations, 2013). They are composed of an outer layer called the epidermis. This body part covers and protects the external body of the organism. The inner layer called the gastrodermis lines the gut. A jellylike material can be found between these two layers, called the mesoglea. The jellyfish has one digestive cavity that is rather simple called the coelenterons. It does the job of the gullet, stomach and intestine. There is only one opening that is shared as the mouth and the anus. Jellyfish have four to eight tentacles that are used to transport food into the mouth. Jellyfish do not have brains instead they have a nerve net. This is used to detect and respond to light, smell and other stimuli (Jellyfish, 2010). (Jellyfish Anatomy, 2013) Jellyfish have no real control over horizontal its horizontal movement. Waves and current aid in horizontal movement while muscles found in the hood (bell) of the organism move the jellyfish vertically. Muscles found in the hood contract and relax pushing the jellyfish through the water. This pulsating rhythm can be very important because jellyfish are light sensitive. The pulsating movement allows the organism to dive deeper into the water allowing it to get away from the suns ray (Jellyfish, 2010). Jellyfish have a special apparatus called a cnidoblast, a venomous mechanism used for defense and feeding. Inside the cnidoblast is a small structure called the nematocyst. This is adapted with a trigger and a stinging structure. Nematocysts consist of a hollow coiled thread with barbs that lines its length. These are found on the tentacles or the oral arms of the creature. One tentacle can contain hundreds or thousands of nematocysts embedded in the epidermis of the jellyfish. These mechanisms are activated when the tentacles make contact with an object. The nematocyst forces a stinging thread to quickly uncoil acting as “small harpoons, firing into the prey, injecting paralyzing toxins” (Jellyfish, 2010). Jellyfish have adapted to life in all types of water. They do not have a complex digestive system and thrive with a gastrodermal lining which absorbs the nutrients needed. Jellyfish do not have a need for a respiratory system because gas is able to circulate through the organism’s thin layer of skin. Due to all these adaptations, jellyfish have been able to survive thousands of years and remain plentiful (Jellyfish Adaptations). References Animal Corner. (2103). Jellyfish anatomy [image]. Retrieved August 30, 2013 from http://www.animalcorner.co.uk/marine/jellyfish/jellyfish_anatomy.html Dickerson, N. (2013). Jellyfish adaptations. Retrieved from http://www.jellyfishfacts.net/jellyfish-adaptations.html Whitaker, D. J. (2010). Jellyfish. Retrieved from http://www.dnr.sc.gov/marine/pub/seascience/jellyfish.html