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Lacking paired fins, [20] adult lampreys have one nostril atop the head [21] and seven gill pores on each side of the head. [12] The brain of the lamprey is divided into the telencephalon, diencephalon, midbrain, cerebellum, and medulla. [22]
In addition to the absence of jaws, modern agnathans are characterised by absence of paired fins; the presence of a notochord both in larvae and adults; and seven or more paired gill pouches. Lampreys have a light sensitive pineal eye (homologous to the pineal gland in mammals).
Because of shared features such as paired fins, the origins of the jawed vertebrates may lie close to Cephalaspidomorphi. Many biologists no longer use the name Cephalaspidomorphi because relations among Osteostraci and Anaspida are unclear, and the affinities of the lampreys are also contested.
The sea lamprey has an eel-like body without paired fins. Its mouth is jawless, round and sucker-like, and as wide or wider than the head; sharp teeth are arranged in many concentric circular rows around a sharp, rasp-like tongue. There are seven branchial or gill-like openings behind the eye. Sea lampreys are olive or brown-yellow on the ...
Like all lampreys, these fish lack paired fins and possess a circular sucking disc instead of jaws. They have a single nostril and seven small gill slits on either side behind the eye. The teeth are sharp and these fish can be told from the rather smaller brook lamprey (Lampetra planeri) by the fact that the two dorsal fins are more widely ...
The Caspian lamprey is a slim-bodied, eel-like fish that grows to a length of about 40 cm (16 in). The longest recorded specimen was 55 cm (22 in) long and weighed 206 g (7.3 oz). Like other lampreys, it has no jaws, but it has a round oral disc surrounding the mouth. Inside this it has several radiating rows of tiny, backward-facing teeth.
Though common and diverse during the Silurian and Devonian, jawless fish are today represented only by lampreys and hagfish, both groups being quite specialized.Lampreys have seven gill pouches (whereas jawed fish have only five), no paired fins, and a rudimentary skeleton of cartilage.
Pacific Lamprey are a part of the Family Petromyzontidae and are one of six species within the genus Entosphenus. [4] Pacific lampreys grow to about 80 cm (31 in) as adults. They are anadromous and semelparous. They have slender, elongated bodies with two dorsal fins arising far back on the body.