Which one of the following animal phyla is the latest by chronological order of discovery?

Let's look at the discovery timelines of these animal phyla:
* Kinorhyncha was discovered and described in $1841$ by Édouard Dujardin.
* Pogonophora was identified in $1914$.
* Loricifera is one of the most recently established phyla, discovered in $1983$ by Reinhardt Kristensen.
* Ctenophora is an ancient group known classically since the early $19^{\text{th}}$ century.

Thus, Loricifera is the latest phylum by discovery.