weird little bugs

Im my tank there are small little bugs that look like tiny mantis shrimp, one time i had a hermit realese tons of little things im asumeing they where more hermits, these little bugs had a feast on them i never noticed them untill i added a ton of shells on top of my sand ive also noticed bristle worms in the shells as well with other weird little bug like things there has allso been a wierd blue bug that would spaz on the glass and jump arround real fast.....any idea

 

sounds like an amphipod -

http://oceanexplorer.noaa.gov/explorations/02arctic/logs/aug26/media/amphipod_500.jpg

 

And, if you look between the rocks near the bottom, you will most likely see what appears to be miniature cleaner shrimp, and they are mysids.
Sometimes when flake food circulates around their environment, they hop on and feed while the flake is swirling around. Kind of neat to watch.

 

how bad are plate worms todau i noticed some big ones under neith my rock iv never moved b4 had to tare appart my tank to catch some killed damsels

 

+1 on amphipods a good thing for sure.