most efficient reproductive system is present in the animals of coelenterata /nematoda /some annelida /platyhelmenthis???????

Most effective reproductive system is found in Phylum Platyhelminthes. Platyhelminths are segmented worms and each segment has complete reproductive system and is hermaphroditic i.e.contains both male and female reproductive system. In liver fluke, where segments are absent entire body in a mature fluke contains reproductive organs. They can produce a large quantities of egg every time.