Larval nematode parasites (Spiruroidea: Cystidicolidae) are recorded for the first time in Octopus vulgaris Cuvier, 1797 in the northeastern Atlantic Ocean. Prevalence was 16% and mean intensity was 1.46 worms/host. Body length of larval nematodes ranges from 8.3 to 9.3 mm, with a distance from the anterior end to nerve ring from 187.5 to 200 microm, and to excretory pore 194.6-350 microm. Anatomical characteristics, such as deirid, nerve ring, cephalic alae, excretory pore, pseudolabia amphids, sclerotized protuberance, and anus, examined using light microscopy (LM) or scanning electron microscopy (SEM), are illustrated. The nematode was designed as a cystidicolid "Type A" larva. The hemocytic infiltration present in the host tissue around the nematode capsule and the mechanical compression in the infected organs denote the pathogenicity of this nematode. In the study area, O. vulgaris may play the role of an intermediate or paratenic host in the nematode life cycle.