Dicyemids are common parasites found in the kidneys of many cephalopods. Species identification previously relied on old species descriptions containing considerable confusions, casting doubt on taxonomy and identification. Detailed morphological description and genotyping of all developmental stages are required for an exact taxonomy. To this end, we undertook the redescription of the dicyemid Dicyemennea eledones (Wagener, 1857), infecting the cephalopod Eledone cirrhosa (Lamarck). Samples were collected off Concarneau in the Bay of Biscay, France, and off La Goulette in the Gulf of Tunis, Tunisia. Dicyemennea eledones is a large species, with adults reaching c.7,000 μm in length. The vermiform stages are characterised by having 23 peripheral cells, a conical calotte and an axial cell that extends to the base of the propolar cells. An anterior abortive axial cell is present in vermiform embryos. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell and the refringent bodies, which were not always seen, are possibly liquid. For the first time, an 18S rDNA sequence is generated for D. eledones, illustrating genetic differences with the other dicyemid 18S rDNA sequences available in databases. This sequence can now be used for D. eledones barcoding, making the identification of the species easier and more reliable.