Boss

Boss (ボス Bosu) is a very large beetle, probably unique. Unlike other beetles, he continues to grow and to change shell even as an adult, this causing his unusual giant dimensions. He lives in Little East Blue with Yoko, an orphan girl who found him in the forest some time after her father's death and got attached to the beetle seeing in him her lost dad. Since then, Boss protects the island from the pirates. He becomes stronger every time he grows up (once a month), so he's a very powerful fighter, capable of emitting fire from his horn. He has an incredible stamina, which allowed him to resist to Franky's Coup de Vent and Luffy's Gomu Gomu no Bazooka without serious wounds. According to Amigo Pirates, he's been stolen from Shiki the Golden Lion, but the events are so far unknown.