Fenner's rock

named for the xeno-biologist Rivoc Fenner, this unusual creature resembled a collection of lichen- and moss-covered stones. They subsist on the lichens, moss, and algae which attach to their bodies, moving slowly over real rocks to find food. They lack true limbs, instead having a pair of appendages which they use to drag themselves along. The mouth of a Fenner's Rock is filled with huge teeth, but the teeth are formed from soft cartilage and were ineffective against most creatures. Most scientists believed them to be silent creartues, but many have observed groupings of Fenner's Rocks "singing" to each other. The exact purpose behind the sounds is unknown. These creatures could be found on a number of planets, and were considered a nuisance on some world because they multiply rapidly, damming up natural waterways and producing semi-toxic bacteria.