Cephalaspides

(also Osteostraci), a subclass of extinct lower vertebrates of the superclass (or branch) Agnatha. The subclass existed from the late Silurian to late Devonian. The animals measured as much as 60 cm in length. The head was flattened and enclosed in a bony shield, which sometimes also enclosed part of the torso. In cross section the torso was flattened or triangular. The eyes were located close to the axis of the animal’s body. There were up to ten pairs of gill openings. Pectoral fins were frequently present, but ventral fins were absent. The caudal fin was heterocercal.

The animals lived in bodies of fresh water and in brackish lagoons. They burrowed in the silt and fed on organic substances and small organisms. Several orders, with a total of approximately ten families, were included in Cephalaspides. The Cephalaspides and several other groups were previously assigned to the group Ostracodermi. The Lower Devonian deposits of the Svalbard Archipelago and Great Britain are richest in the fossil remains of Cephalaspides. Fossils have also been found in mainland Norway, Germany, and Canada. In the USSR fossils have been found in Silurian deposits on Saaremaa Island, where there are abundant remains, and in Lower Devonian deposits near the Dnestr River. Deposits have also been found in the northern Timan Ridge and in Tuva.