The male and female of Rhizorhina serolis sp. n. are described and figured. This copepod is parasitic on the isopod Serolis bromleyana, from Chatham Rise, between Chatham Island and New Zealand.
Sphaeronella serolis Monod is recorded from the same host and locality. The hitherto unknown larva and male pupa of S. serolis are figured.
The male of Rhizorhina shows a great similarity to the larva of Sphaeronella, and is considered to be neotenic.