There is a branch of the Leon Guerrero clan called the familian Alimåsak.
But it could be that this branch of the Leon Guerreros were so-called because of their Borja ancestor. As seen in this court document from 1902, a Manuela de Borja was better-known-as Alimasag.
Then, someone we know for sure was better-known-as Alimåsak, Juan José de León Guerrero, had Borja as a middle name; meaning, his mother was a Borja. It's possible Juan José's mother was sister to Manuela de Borja, known as Alimåsak. It does happen that a family takes on the mother's family nickname over the father's.
The alimasåk is a species of crab. The story I heard says that one of the family ancestors had a little too much of the good stuff to drink, and was with others socializing on the beach. When he got up to walk, he didn't have much of a balance and started to sway to and fro as he walked. This reminded the others of the way the alimåsak walks sideways, and they laughed and started calling him alimåsak.
But, according to pre-war author Laura Thompson, the nickname came from a member of the family waving his arms while dancing in a way that reminded an onlooker of an alimåsak crab.