Bizarre but true fact re: cories. Go to planetcatfish.com and look at the genus thumbnails for Corydoras, and look at C. arctuatus and C. narcissus. C narcissus is the 'long nosed' version of arctuatus. They are separate species , and do not/can not hybridise, but form shoals together in the wild. I believe the long nosed version is the less numerous of the two.
This long nosed/short nosed twin species deal shoaling together happens a lot apparently, and noone is sure why. I have anarticle by David Sands on it somewhere