AIn an interview lead writer Mac Walters explains that Reapers take the form of the species used to build the Reaper. However, this is only the core. A complete Reaper looks like an insect, more precisely a reaper cuttlefish, this is because the Reapers were modeled after the Leviathans, an advanced race of aquatic "apex predators". Subtle differences can be observed, however. While Sovereign and most other Reapers have five tentacle like appendages on its front end, Harbinger has only four, with two sets of four glowing, yellow lights embedded symmetrically on the lower dorsal surface of the body.The interview: http://www.gameinformer.com/b/news/archive/2011/04/21/mass-effect-a-q-amp-a-for-hardcore-fans.aspx