Crabber

Crabbers are a type of Crab found in beach galaxies of Super Mario Galaxy and Super Mario Galaxy 2. They are shown to have a big left pincer and a small left one. Mario has to defeat the creature by Spinning at it's rear. This is a little tricky, as Crabbers always face Mario. So, Mario first has to spin in it's face, or rather Jump on it. When doing one of these move, it defends it with it's big pincer, leaving the rear behind. When the Crabber defends its face, its sight doesn't follow Mario, so he can Spin at it's rear to defeat it.

Crabbers come in two colors: red and blue. Red Crabbers are less skittish than blue ones, so they are easier to defeat, and also leave Star Bits behind when defeated. Blue Crabbers are harder to defeat, and leave a 1-Up Mushroom behind when defeated.

Super Mario Galaxy
Crabbers are found in galaxies with a beach, such as Deep Dark Galaxy. They walk sideways like normal crabs, and try to defend their rear by facing Mario when close.

Super Mario Galaxy 2
Crabbers reappear once again, in some beach galaxies such as Starshine Beach Galaxy. Yoshi also appears in this galaxy, and can stuff Crabbers in his mouth. Yoshi cannot convert them into Star Bits, but can spit out their big pincer in the same way as a Spiny Egg or Bullet Bill. The pincer acts as a boomerang, as it flies in a direction and returns to the direction where it is spitted out.

Surprisingly, several Crabbers also appear in a Prankster Comet mission of Boulder Bowl Galaxy, named Rolling Crabber Romp. Rock Mario must defeat 30 Crabbers in a minute to get the Power Star.

Trivia

 * Coincidentally, another species of crab, the Sidestepper, could appear in red and blue as well.