Sepiola rondeletii Leach, 1817

Sepiola rondeletii is a species of dwarf bobtail in the family Sepiolidae (bobtail squids). Males have a compact body which can reach a maximum length of 2.5 cm (excluding arms), while females of this species are elongated and therefore reach up to 6 cm in length. Dwarf bobtails have eight arms and two tentacles. While the arms are lined with two rows of suckers along their entire length, the tentacles only possess suckers on their club-shaped tips and those are arranged in eight rows. In the rear end of the mantle (which covers the internal organs such as gills), Sepiola rondeletii possesses a pair of symmetrically arranged, lobe-shaped fins that are used for steering while swimming and make the impression that dwarf bobtails are "flying" through the water.

Like many other cephalopods, dwarf bobtails have the ability to change the color of their skin dramatically. They accomplish this feat with the help of specialized cells known as chromatophores and iridocytes. The chromatophores of this species are particularly large among cephalopods, they are visible to the naked eye. Chromatophores contain a dark pigment, which appears differently depending on whether the cells are contracted or relaxed. In the latter case, they are colored in different hues of brown. By relaxing all chromophores, dwarf bobtails can adopt a dark color. On the other hand, if the chromophores are contracted, the overall color of the skin is much lighter.

This species occurs in the whole Mediterranean Sea as well as the East North Atlantic Ocean. It was recorded at a maximum depth of 450 m but usually occurs in less than 50 m. They are a nocturnal species and burrow in sandy ground during the day in order to evade predation. During the night they swim freely in search of food, which comprises small crustaceans such as shrimp, as well as small fish. Since they stay close to the ground, dwarf bobtails are generally classified as a benthic species.

Like many other cephalopods, bobtail squids possess a highly evolved nervous system and are therefore considered very intelligent animals. They have two large lens eyes which are anatomically similar to those of vertebrates, although they have evolved independently. Sepiola rondeletii harbors bioluminescent bacteria which live in internal pockets close to the ink sac known as the light organs, which emit light continuosly. When attacked, dwarf bobtails can release ink from their body, which produces a dark cloud in the water to startle predators.