What a fun find on the beach! This is part of a stomach and the pyloric caeca of a fish.
Here is some quick information from Florida Fish and Wildlife Conservation Commission:
Pyloric Caeca:This organ with fingerlike projections is located near the junction of the stomach and the intestines. Its function is not entirely understood, but it is known to secrete enzymes that aid in digestion, may function to absorb digested food, or do both.