Osteology of hyobranchial arches in eurypterygian fishes

The osteology of the hyoid and branchial arches in several representatives of eurypterygian fishes were examined. The hyoid arches consist of a single basihyal and urohyal, and the arch on each side consists of a dorsal and a ventral hypohyal, an anterior and posterior ceratohyal, an interhyal, and branchiostegal rays that are borne on the ceratohyals. The branchial arches consist of three single, separate, and ossified basibranchials, and in most taxa the arches on each side consist of three hypobranchials, five ceratobranchials, four epibranchials, four pharyngobranchials, and associated teeth and tooth plates. The fourth pharyngobranchial is absent or reduced in all the studied taxa, but the fourth pharyngeal tooth plate is usually present. Gill rakers and small toothplates are present on the branchial arches of most taxa.