Shellcreeper

...aka: Kame-San (Japanese Famicom version)
...aka: Turtle (US NES version)

Overview

A low-slung, green-shelled turtle that roams the sewers.

Mario Bros.

Shellcreeper is the first enemy to appear in the game. It comes out of the pipes. Hit it from below to flip it over and then run into it to defeat it. If you fail to run into it, the Shellcreeper jumps out of its shell (wearing shorts), flips its shell over and then continues moving, this time faster than before.

Notes

The Shellcreeper is clearly a conceptual ancestor of the Koopa Troopa. Aside from both being turtles, Shellcreeper also wears shorts when outside of his shell - something the Koopa Troopas started doing in Super Mario World 2: Yoshi's Island (in Super Mario World they wore vests).

In later remakes of Mario Bros., Shellcreeper was replaced by Spiny.