Megadenus is a genus of sea snails, marine gastropod mollusks in the family Eulimidae.

[1] Species within this genus include the following:[1] [2] This parasite was discovered to reside in the cloacal chamber of the black sea cucumber Holothuria atra.

M. atrae differs from the other species by having moderately long and thick developed collar of the proboscis that contains a constricted apical pseudopallium.

M. atrae is found in black sea cucumbers of which are in India, Japan, Australia and New Caledonia.

Furthermore, this limits its ability to mate and confines it to specific water temperatures of which its host must be in alongside the opposite sex.