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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]
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 ...
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.
Adult river lampreys measure from 25 to 40 cm (10 to 16 in) for the sea-going forms and up to 28 cm (11 in) for the lake forms. The very elongate body is a uniform dark grey above, lightening to yellowish off-white on the sides and pure white below. Like all lampreys, these fish lack paired fins and possess a circular sucking disc instead of jaws.
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.
The jawless fish (hagfish and lamprey) do not have appendage-like fins. They may not have lost them, but rather, simply retained the form that vertebrates had before the evolution of limbs. [1] There are also a number of fish with elongated bodies that have no fins or reduced appendage-like fins, for example eels and swamp eels. [2]
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.
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.