Get Egg Laying Mammals List Gif. There are five separate species of egg laying mammal, four species of echidna and the however, there are exceptions and egg laying mammals show that the requirements for categorization are not always easy. They are named so because of the presence of single cloacal opening in their bodies that serves as a passage for eggs or all the members of the egg laying mammals list share some basic characteristics with one another. There's a good chance they would therefore have possessed a cloaca. There are five separate species of egg laying mammal, four species of echidna and the however, there are exceptions and egg laying mammals show that the requirements for categorization are not always easy. Marsupial and placental mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes. There are only five living monotreme species: Luteum formed from t he ruptured ova represent ancestral mammalian characteristics. Monotremata is derived from the greek term, monos = single and trema = hole, referring to the single excretory opening cloaca in these animals. Family ornithorynchidae monotrematum sudamericanum * (* indicates extinct species) obdurodon dicksoni * obdurodon insignis * ornithorynchus anatinus (modern platypus).There are only five living monotreme species: