Ceramic Aquarium Shrimp Shelter - Semicircle Part # 11497-01
 
Size Approx - 5.5cm D x 5.5cm W x 2.75cm H  /   2" D x 2" W x 1" H
Provides refuge and protection from predators
Can provide substrate for fine algae or bio-film
Seclusion for molting / female with eggs