The Muschelkalk is famous for its well preserved lobsters. Like the glypheid genera Pseudopemphix, Aspidogaster, and Litogaster, and the nephropid Lissocardia, the spiny lobster Pemphix has a calcified carapace and is commonly preserved as exuviae. Other than these, actively swimming penaeid shrimps are extremely rare. This is also the case with marine sea slaters (Isopoda), horseshoe crabs (Limulida) and the extinct sea helmets (Cyclida). In contrast, the small shell-bearing conchostracans and ostracods occur abundantly on certain bedding planes. Conchostracans, which are distantly related to water fleas, have a bivalved carapace. The minute ostracods have two calcified valves, which enclose the entire body.