Sea levels were high, and there was a great variety of fish and other marine organisms. The Devonian fish included the Agnatha (jawless fish), the Acanthodii (spiny fish), the Placoderms (armoured fish), the Chondrichthyes (cartilaginous fish), and the early Osteichthyes (bony fish). The Devonian strata are divided into lower, middle and upper subdivisions.