That is a skimmer. The dead giveaway is the collection cup and drain. This looks like a good old fashioned Beckett Skimmer. http://myreefcreations.com/knowledge-base/MR-R-Skimmer.html">http://myreefcreations.com/knowledge-base/MR-R-Skimmer.html</a>
Beckett skimmers used high pressure pumps to push water through a Beckett pond fountain nozzle through the hole in the top of the black box. They were noisy, costly to operate and were replaced by needle wheel style skimmers. If you are a DIY type person, you could purchase a needle wheel pump and feed the output into the black box and end up with a good skimmer.