Together with "Little Crab 2", they collect decoration ornaments that they both refer to as treasures. Succeeding Little Crab 1's game of finishing their jokes, they agree to give you the ornaments to decorate Big Crab's new home, both voicing they hope you put their stuff to good use.
Little Crab 1 is the more playful and careless one of the Crab Couple. Even though having collected decorative ornaments with Little Crab 2, and hearing their displease when being requested to give away their treasure, they simply refer to Little Crab 2 as being "crabby" and offers Super Moshi the treasures if they correctly finish their joke with punchlines.
Although all their jokes being negative towards crab kind, they only show being uncomfortable with the final punchline that claims that crabs steal. This might have to do with the mission itself, where you accuse specifically the Big Crab of stealing the Googenheim.
Both the Little Crabs have a similar design to Herman Crab, only difference being the house on top of them. They both have a straw roof beach house as their shell/home or differing design. Little Crab 1 has a more hut-like design with no clear idea of an entrance.