Found this...
Gotta love a hobby you can enjoy for a decade and still pick up the odd bit of new info...
http://reefkeeping.com/issues/2004-09/rs/index.php
from the article
"One very small group of oddball amphipods is called the Ingolfiellidea. These animals normally live between and on sand grains, and to the best of my knowledge, they have never been seen in aquaria. The other two groups of amphipods are both ecologically important and diverse. They are the Hyperiidea and the Caprellidea. The hyperiids live in the plankton, and many are predatory or parasitic on gelatinous zooplankton..."