Microcleidus melusinae was named by Vincent et al. (2019) [Small-bodied plesiosauroid with the following unique combination of characters: unconstricted snout (between the premaxilla and maxilla), weak participation of the prefrontal to the naris margin, frontal excluded from the orbital margin, posteriorly elongated jugal that terminates anteriorly around the posterior orbital margin and is excluded from the orbital margin, postorbital posterolateral process long, parietal foramen situated just posterior to the parietal frontal suture, absence of an anterior interpterygoid vacuity, pterygoids do not meet each other posterior to the posterior interpterygoid vacuity, a keeled parabasisphenoid, a smooth enamel on the labial surface of the tooth, 30 postaxial cervical vertebrae, short anterior cervical centra, absence of a longitudinal ridge on anterior cervical vertebrae, and an anteroposterior constriction at the base of the dorsal neural spines. Microcleidus melusinae differs from the other species of Microcleidus as it possesses a slightly longer anterior extension of the jugal than that reported for M. brachypterygius, a shorter participation of the prefrontal to the naris margin than that observed in M. brachypterygius, a pineal foramen contra that reported in M. tournemirensis, a rim of the pineal foramen that is raised dorsally from the surrounding surfaces contra that observed in M. brachypterygius, a frontal excluded from the orbital margin contra that reported for M. tournemirensis and M. homalospondylus, a smooth enamel on the labial surface of the tooth contra M. brachypterygius and M. tournemirensis, and 30 postaxial cervical vertebrae contra that observed in M. homalospondylus and M. tournemirensis.]. Its type specimen is MNHNL TV434, a partial skeleton (Skull with a partial postcranial skeleton), and it is a 3D body fossil. Its type locality is Sanem, which is in a Falciferum offshore limestone in Luxembourg.