Sushi roll, also known as the nigiri sushi or just plain nigiri, is the most basic form of the Edo style sushi. Nigiri is the noun format of the verb nigiru which means to squeeze or to grasp. A nigiri consists of sushi rice lightly squeezed together with a main ingredient (frequently a sashimi or raw fish), so they stick together and can be eaten as a whole.
The commonly seen nigiri has gone through a couple modifications for about 200 years and the size and shape has changed a bit. In the early days of the Edo period a nigiri sushi was about 3 to 4 times larger than the commonly seen nigiri today. One or two nigiri were practically enough for a whole meal. This took away the enjoyment of trying out many different ingredients and they started to become smaller later on, but the main reason they were big was because there were only a few ‘official’ ingredients of Edo style sushi in the days when refrigerators were not yet invented. Ingredients that can be served any day were limited to the raw fish that still taste good after being be cured, or immersed in soy sauce (zuke method), or cooked. Many raw fish dishes existed at the time, but they were difficult to have them available every day and any time without refrigeration.
Besides the reduction of size, the nigiri also had four distinct shapes that eventually settled to one style. They are all named by the shape of the ingredient that lays on top of the sushi rice. The commonly used shape today is called the funazoko, or ship hull. The jigami, or a folding paper fan is sometimes used in traditional style sushi restaurants. The kushi or hair comb accessory is a modification of the older oshizushi (Osaka style pressed sushi) and has a flattert op. The tawara or a straw sack used to hold rice, is the most primitive style which the ingredient covers the most of the exposed surface of the sushi. This style was first created to cover the sticky sushi rice so it can be handled easier when consumed on the streets. The tawara was the predecessor to the other three styles but eventually disappeared, since the seaweed used for sushi rolls made handling sushi even cleaner.