Ostenocaris

Ostenocaris is a Jurassic species of giant Thylacocephalan crustacean, sufficiently distinct from its relatives to be placed in its own family, Ostenocarididae. It is believed to be a bethonic animal and one of the most important necrophagous animals of its environment. Originally Interpreted as a bizarre barnacle. Ostenocaris is the most common fossil of the formation, and the main identified thylacocephalan from the formation. In the first interpretations, the genus was shown as a filter-feeding organism, which used the cephalic sac as a burrowing organ to ensure adhesion to the substrate. Based on the presence of Coprolites associated to the genus, with abundant masses of alimentary residues (hooks of cephalopods, vertebrates, remains of Crustacea) in the stomach of these organisms, Ostenocaris cypriformis was probably a necrophagous organism, and the cephalic sac can be tentatively interpreted as being a burrowing organ employed during the search for food, or as an organ of locomotion with intrinsic motility. Later studies agree that cephalic sac is actually extremely large compound eyes.

Distribution
Ostenocaris lived during the Sinemurian age of the Lower Jurassic, and has been found in rocks at two sites in the Italian Lombardische Kieselkalk Formation. This formation is known for its good preservation, with fossils of annelids, fishes, and plants, representing a relatively depth shelf deposit, where Thylacocephalans are the most abundant organisms. A second species found in the Middle Jurassic (Callovian) La Voulte-sur-Rhône Lagerstätte of France, formerly known as Clausocaris ribeti was reclassified as second Ostenocaris species. This species lived in a bathyal zone environment, in a depth most  probably  exceeding  200 m.