The common ingredient in all the different kinds of sushi is sushi rice. Variety arises in the choice of the fillings and toppings, the other condiments, and in the manner they are put together. The same ingredients may be assembled in various different ways:
Nigirizushi (hand-formed sushi). Arguably the most typical form of sushi in Japan, it consists of a oblong mound of sushi rice which is pressed between the palms, with a speck of wasabi and a thin slice of a topping (neta) draped over it, possibly tied with a thin band of nori. Assembling nigirizushi is surprisingly difficult to do well. It is sometimes called Edomaezushi, which reflects its origins in Edo (present-day Tokyo) in the 18th century. It is often served two to an order.
Gunkanzushi (battleship roll). An oval, hand-formed clump of sushi rice (similar to that of nigirizushi) is wrapped around its perimeter with a strip of nori, to form a vessel that is filled with some ingredient—e.g. roe, natto, or less conventionally, macaroni salad.
Makizushi (rolled sushi). A cylindrical piece, formed with the help of a bamboo mat, called a makisu. Makizushi is generally wrapped in nori, a sheet of dried seaweed that encloses the rice and fillings. Occasionally the nori is substituted with a paper thin fried egg wrapper. Makizushi is usually cut into six or eight pieces, which constitute an order. During the Setsubun festival, it is traditional to eat the uncut makizushi in its cylindrical form. Makizushi superficially resembles the Korean dish gimbap.
Futomaki (large rolls). A large cylindrical piece, with the nori on the outside. Typical futomaki are two or three centimeters thick and four or five centimeters wide. They are often made with two or three fillings, chosen for their complementary taste and color.
Hosomaki (thin rolls). A small cylindrical piece, with the nori on the outside. Typical hosomaki are about two centimeters thick and two centimeters wide. They are generally made with only one filling, simply because there is not enough room for more than one.
Kappamaki, filled with cucumber, is named after the Japanese legendary water imp, the kappa.
Temaki (hand rolls). A large cone-shaped piece, with the nori on the outside and the ingredients spilling out the wide end. A typical temaki is about ten centimeters long, and is eaten with the fingers since it is too awkward to pick up with chopsticks.
Uramaki (inside-out rolls). A medium-sized cylindrical piece, with two or more fillings. Uramaki differ from other maki because the rice is on the outside and the nori within. The filling is in the center surrounded by a liner of nori, then a layer of rice, and an outer coating of some other ingredient such as roe or toasted sesame seeds.
Oshizushi (pressed sushi). A block-shaped piece formed using a wooden mold, called an oshibako. The chef lines the bottom of the oshibako with the topping, covers it with sushi rice, and presses the lid of the mold down to create a compact, rectilinear block. The block is removed from the mold and cut into bite-sized pieces.
Inarizushi (stuffed sushi). A small pouch filled with sushi rice and other ingredients (named after the Shinto god Inari, who has a fondness for rice products). The pouch is fashioned from deep-fried tofu, a thin omelet, or dried gourd shavings .
Chirashizushi (scattered sushi). A bowl of sushi rice with the other ingredients mixed in. Also referred to as barazushi.
Edomae chirashizushi (Edo-style scattered sushi). Uncooked ingredients artfully arranged on top of the rice in the bowl.
Gomokuzushi (Kansai-style sushi). Cooked or uncooked ingredients mixed in the body of the rice in the bowl.
Narezushi is an older form of sushi. Skinned and gutted fish are stuffed with salt then placed in a wooden barrel, doused with salt again, and weighed down with a heavy tsukemonoishi (pickling stone). They are salted for ten days to a month, then placed in water for 15 minutes to an hour. They are then placed in another barrel sandwiched and layered with cooled steamed rice and fish. Then this mixture is again partially sealed with otosibuta and a pickling stone. As days pass, water seeps out, which is removed. Six months later, this “funazushi” can be eaten, and it remains edible for another six months or more.
References: Barber, Kimiko;Takemura, Hiroki (2002). Sushi: Taste and Technique, DK Publishing. ISBN 0-7894-8916-3.
Kawasumi, Ken (2001). The Encyclopedia of Sushi Rolls, Graph-Sha. ISBN 4-88996-076-7.