Ceramic Aquarium Shrimp Shelter - Chimney Part # 11991-04
 
Size Approx - 3.5cm D x 3.5cm W x 6cm H  / 1.75" D x 1.75" W x  2.5" H 
Provides refuge and protection from predators
Can provide substrate for fine algae or bio-film
Seclusion for molting / female with eggs