Segmented Crawbster

The Segmented Crawbster is a crab-like creature has one large arm and an exceedingly smaller left arm. It also has a rather thick shell protecting it. This creature rolls after the active leader, occasionally crushing Pikmin with its hard shell. If it crashes into a wall, it can cause boulders to fall. It will then struggle to get back up in an upright position, and while doing so will expose its weak spot: its flashing underbelly. Eventually, it will then get back up and swing its large arm around back and forth two or so times and continue its assault. Once defeated, the Segmented Crawbster will groan and squeal as it is underbelly explodes violently, spewing goo particles all over the immediate vicinity.

Olimar's notes

 * "This gigantic beast is wrapped in a hard shell. In an atypical evolution, the right front leg of this creature is hypertrophic, taking on the function of an arm, rather than a leg. Its asymmetric physical development is unique in the natural world. One unlucky explorer's incorrect conclusion that this creature adheres to a pattern of peaceful, quiet behavior led to an unfortunate incident. In fact, this beast exhibits intensely hostile, aggressive tendencies, aiming at prey and ramming them at full speed."

Louie's notes

 * "Dessert meats are all the rage on Hocotate. When the planet's finest chefs hear about the kind of sorbets, pies, and parfaits you can make with the claw meat on this sweet beast, they'll clamor for every morsel we bring home!"

Pikmin: Redemption
These are more common and sometimes when your on a sublevel above where you fight one you can hear this creature pounding the floor and walls.

Pikmin: Sinister Incinerator
Although Segmented Crawbsters can be fought as recurring minibosses in a few caves like a variety of other foes, the one that serves as the boss of the Dark Wetland Cave in the Ancient Wetland and is intentionally much harder to defeat, as it holds one of the Dark Spores. This Crawbster, in particular, is called the Reconstructed Crawbster.

Pikmin: The After Years
Although the Segmented Crawbster appears twice in the game, once in the Cave of Screams and another time in the Rememberance Ravine, it has a new member in its family called the Clambering Crawbster that appears on the final sublevel of Crawbster Cave.

Pikmin Galaxy Adventure
It doesn't appear simply as a boss. It appears multiple times, but it is much easier than in Pikmin 2. Various Subspecies exist such as the Jungle Crawbster.