Resurrection of Alebion difficile (van Beneden, 1892) (Copepoda: Siphonostomatoida: Caligidae) with notes on other species of Alebion Krøyer, 1863 collected from elasmobranchs off South Africa and an updated key of the adult females.

Alebion Krøyer, 1863 is one of the genera of the Caligidae Burmeister, 1835 and can easily be distinguished from other genera by the presence of modified exopodal spines on legs 1-3. Currently there are eight recognised species infecting a variety of elasmobranch hosts. Alebion difficile (van Beneden, 1892) is resurrected based on the difference in the structure of the spermatophores on the genital complex of the female but also the difference in the relative lengths of the posterior processes of the genital complex, the lateral processes on the first abdominal somite and the caudal rami. Additionally, the adult male of A. difficile is described and illustrated and notes provided about the morphology of the sub-adult females and males. Other Alebion species and their hosts collected off South Africa are reported and an updated key to the adult females of the species of Alebion is provided.