Thelodus is an extinct genus of primitive jawless fish that lived in the Silurian period. Fossils have been found worldwide.
Thelodus belonged to the Thelodonti, a group of jawless fish lacking the armored plating characteristic of the related Heterostraci. The position of Thelodus`s mouth suggests that it fed on the ocean floor. Despite this lifestyle it was also a good swimmer, as indicated by its elongated lower caudal lobe and stabilizing dorsal fin, anal fin and paired pectoral fins.