Lampreys, Petromyzontoidea

Abstract

The lampreys represent the most primitive group of presently living vertebrates. They are water inhabitants with elongated, eel-like bodies which lack paired fins (Fig. 10.1). In contrast to amphioxus, the head of the lamprey bears a number of special sense organs (nose, eyes, ears). The information gathered by these organs is relayed over the cranial nerves to centres in the enlarged rostral part of the CNS. There is a single nasal orifice high on top of the head and slightly behind this opening; a patch of pigment-free skin marks the position of the well-developed third or pineal eye. The animals lack jaws, having instead a large disc-shaped sucking mouth with many horny teeth. Many, but not all adult lampreys are predacious. The predacious varieties attach themselves to fish using their sucking mouths; then they produce a wound by rasping movements of a tongue-like structure which bears numerous sharp denticles. Finally, the lamprey ingests the blood and tissue fragments of its prey.