I have legs and a back. I am not alive.You can sit on me, but I am not a sofa. My name begins with’ch’. Who am I?

 I am an ocean animal. I have fins, but I do not have a shell. My name begins with‘sh’.Who am i?     

I am a game for two players. I am played on a board. My name begins with ‘ch’ I am not checkers. Who am I?       

I am a mammal. I have four legs. My body is covered with wool. My name begins with ‘sh’. Who am I ?