What happened: i have aquatic turtles together and have had quite awhile in a childs pond?

my water turtles i guess mated. but after few min. theywere connected as they swam around. the top one smaller just drug along. shortly then some of the others started chasing the smaller one as she disconneted and i picked it up it or she or he had a large red thingie hanging out of it. it looked like a liver. damm i have it in a seperated bucket. just looked and the red thing good sized, went back i. i have no clue as to what that is and what happened. please help if you have any knowledge for this scarey incident. thanks so much.