Ebi nigiri is a traditional type of nigiri sushi. It consists of hand-pressed sushi rice that's topped with butterflied shrimp. Any large shrimp will do, but kuruma ebi (Penaeus japonica) is said to be the best. The shrimp is skewered, boiled, chilled in ice (just until the exterior is cold, while it remains warm inside), and it's sometimes marinated in ginger juice in order to become more firm and have a bit more flavor.