Echinocephalus caniculus n. sp. (Nematoda: Gnathostomatidae Railliet, 1895) from the lesser spotted dogfish Scyliorhinus canicula (L.) (Elasmobranchii: Scyliorhinidae Gill, 1862) off Tunisia, with a key to species of the genus Echinocephalus.

Echinocephalus caniculus n. sp. (Nematoda, Gnathostomatidae Railliet, 1895) was isolated from the spiral valve of the lesser spotted dogfish Scyliorhinus canicula (L.) from the waters off Kalaat El Andalous, North East Tunisia. This new species is mainly characterized by a cephalic bulb armed with 31-39 transverse rows of uncinated hooks, a comparatively long oesophagus, short spicules and the presence of a gubernaculum. The new species differs from its congeners by having four cervical sacs of almost equal length, a higher oesophagus/body length ratio, the arrangement of the caudal papillae, the absence of a medioventral preanal organ and numerous scattered `pores´ limited to the lateral side of the posterior part of the body. This is the first report of a member of the genus Echinocephalus Molin, 1858 from the Tunisian coast, and a new host and locality record for the Gnathostomatidae. A key to the species of Echinocephalus is provided.