Distinguishing Features
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Support/SkeletonAgnatha are vertebrates with unhitched circular mouth. They lack appendages and have an internal skeleton that is cartilaginous. The adults and larva have a notochord that provides the main support for the bod.
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Gas Exchange/ RespirationThey have seven gill slits where oxygen diffuse. Agnatha breathe by sucking in water through the mouth and into the pharynx, then release water from the gill slits. Before leaving through the gill slits, water must pass through the feather-like gills. When gas exchange occurs, the feather-like structure of the gills increase it surface area, helping the effectiveness of the exchange.
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Transport/CirculationAgnatha have gills and and a single loop circulatory system that pumps into the two chambered heart. Deoxygenated blood goes through the gill capillaries to become oxygenated. The deoxygenated blood then travels through the heart into the body capillaries, where it spreads oxygenated blood around the body.
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Habitat/LifestyleLampreys are found in warm rivers and coastal seas. They are born as larva in freshwater. During the larval stage, lamprey are usually found in muddy rivers or lake bottoms, and feed on microorganisms. This stage can last up to seven years. At the end of the stage, the lamprey changes into an eel-like creature that swims and usually attaches itself to fish to feed
Hagfish are mostly found in cold oceans on the muddy sea floors. They feed on marine worms and other invertebrates. |
Sensory/Nervous SystemThey have a complex nervous system with a brain that connects to a spinal chord. Agnatha also have a peripheral nervous system which includes cranial nerves and spinal nerves. At the head, they have 2 eyes that sense light and do eye stuff.
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Feeding/DigestionThey digest the blood taken from other fish (host) directly in the intestines. This is because they don't really have a stomach. Digestion and absorption all happen in the intestines. Agnatha excrete enzyme and secretions near the buccal cavity (mouth) that break down the hosts blood to prevent it from clotting. The end portion of the intestine digests bacteria, reabsorbs water, and form feces. The last section of the intestine narrows to form a small exit. The result is solid wastes leaving the body.
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Life HistoryLamprey
Lamprey exhibit a larval and adult stage. The larval stage lasts several years during which the lamprey filter-deeds. As adults they feed by parasitism. Adults live in sea waters but return to freshwater to spawn. Fertilization takes place externally. Up to 10,000 eggs can be lain in one spawn. The lamprey will die shortly after spawning. Hagfish Hagfish live on muddy bottoms of the ocean floors. Not much is know about their reproductive habits. No observation of hagfish reproduction has been observed, through studies suggest a seasonal breeding cycles. |
Excretion/OsmoregulationThey have an excretory system that mainly relies on the work of the kidneys. In time of drought, Agnatha burrow in the mud and switch to urea production. They kidney not only sends waste out of then body through the anus, but they play a key role in keeping the amount of salt in the body regulated. These creatures live in both salt and freshwater. The kidneys must work to maintain a balance of salt when in freshwater. When the fish is in salt water, the fish's gills work to keep excess salt out.
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Movement/LocomotionLampreys and Hagfish swim in a rippling motion by moving the tail (caudal fin) back and forth. Parasitic adult lampreys attach to mobile fish so they don't need to swim often.
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