oecilia sphenops is a species of fish, known under the common name molly; it is sometimes called short-finned molly or common molly. They inhabit fresh-water streams, coastal brackish, and marine waters from Mexico to Colombia. The wild-type fishes are dull, silvery in color.

Mollies are similar in appearance to their livebearer cousins, the platy, swordtail and guppies; the molly tends to be slightly larger and more energetic. Many aquarists note the stronger individuality and aggression in keeping mollies versus platies, who appear much more docile.