text: how much do moon jellyfish usually weigh?   jellyfish are very delicate animals whose bodies are comprised primarily of water (~ 96% of their weight is water) infused throughout a network of tissue. thus, water provides virtually all of their structural support (it is their bones), allowing them to grow large, and appear robust, without any rigid tissues. the bodies (the bell) of jellyfish is made of a material called mesoglea. mesoglea is a jelly-like material that is elastic because of there are fibers that connect together in the mesoglea. the other main body part a jellyfish is the gut and it contains mostly water and digestive juices. since most of the material of a jellyfish is the exact density of water. if you weigh water about the same size as the jellyfish you want to know the weight for, you will get weight of the jellyfish. i suggest you weigh some water at home or school that is about the same size as a jellyfish that interests you and you will get an approximate weight of a jellyfish. or the jellyfishes can be grouped with 1 cm intervals and then the number of animals for each size group is recorded. the jellyfish a. aurita can be fixed in 2% buffered formaldehyde. we are proposing the following equation for calculation of biomass of a. aurita, which was developed for a. aurita inhabiting in the black sea: w= 0.12 l 2.58 where w- wet weight in grams, l- length in mm; (measurements range from 6.1 to 151mm)(mutlu, 2001)   these equations should also be developed for the caspian population of a. aurita.   individual jellies typically enjoy a life span of only weeks or months,it is likely that most jellyfish have quite short lives. it must be remembered that the jellyfish stage is only one stage in the life-cycle of most species. for both the true jellyfish (class scyphozoa) and most hydrozoan jellyfish this stage buds off from what is known as a polyp stage. the jellyfish is the sexual stage and is the stage that has mature gametes. the sexes are separate. since jellyfish roam freely in the plankton it is during this stage that dispersal takes place. the young planula larvae settle and grow into the polyp stage which can live for many years. in temperate waters the growing polyp buds off new jellyfish once a year, often in the spring. the young jellyfish grow rapidly through the summer, spawn then usually die. so most jellyfish live less than 1 year.