class AGNATHA
Class Agnatha consists of a group similar to fish, but have very big differences. Most Agnathan species are extinct, but the two living groups of Agnatha are the Lampreys, which reside in both fresh and marine water, and Hagfish, that reside in marine environments.
ECOLOGICAL ROLE
The Agnathan serve as food for seabirds, lobsters, crabs, seals and walruses.
The Agnathan serve as food for seabirds, lobsters, crabs, seals and walruses.
MOVEMENT STRUCTURES/TYPE
Agnathans have a tail and a caudal fin that help with movement in the water. They lack paired appendages. Lampreys swim in a rippling manner using their well-developed dorsal and caudal fins. They use their posterior muscles to twist its tail back and forth, allowing it to move within the water.
Agnathans have a tail and a caudal fin that help with movement in the water. They lack paired appendages. Lampreys swim in a rippling manner using their well-developed dorsal and caudal fins. They use their posterior muscles to twist its tail back and forth, allowing it to move within the water.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
Agnathans are bilaterally symmetrical, elongated, and have cylindrical eel-like bodies. Agnathans lack scales and plates, but instead have slimy skin. Almost all agnathans have no paired appendages, but most have a dorsal or caudal fin. They do not have a distinct stomach, but they have a long gut. They have teeth, but lack jaws that can chew the food. Instead of jaws, they have a cyclotomic (circular) toothed mouth, with which they bore into the side of a fish and suck the blood of their victim. Hag fish slime is used as a defence mechanism. When threatened, they ooze out great amounts of foul slime that keep predators away. They also release the mucus to assist them in escaping from predators.
Agnathans are bilaterally symmetrical, elongated, and have cylindrical eel-like bodies. Agnathans lack scales and plates, but instead have slimy skin. Almost all agnathans have no paired appendages, but most have a dorsal or caudal fin. They do not have a distinct stomach, but they have a long gut. They have teeth, but lack jaws that can chew the food. Instead of jaws, they have a cyclotomic (circular) toothed mouth, with which they bore into the side of a fish and suck the blood of their victim. Hag fish slime is used as a defence mechanism. When threatened, they ooze out great amounts of foul slime that keep predators away. They also release the mucus to assist them in escaping from predators.
SUPPORT
Agnathans do not have internal skeleton made of bone, but instead have one made of cartilage (a cartilaginous skeleton is made up of dense connective tissue). Agnathans have a notochord that remains present throughout their whole life. This notochord is the first primitive vertebral column (spine). The notochord provides support to the hagfishes body. Unlike true vertebrates, hagfishes do not replace the notochord with a vertebral column during development. Lampreys notochord is surrounded by a cartilaginous structure called an arculia.
Agnathans do not have internal skeleton made of bone, but instead have one made of cartilage (a cartilaginous skeleton is made up of dense connective tissue). Agnathans have a notochord that remains present throughout their whole life. This notochord is the first primitive vertebral column (spine). The notochord provides support to the hagfishes body. Unlike true vertebrates, hagfishes do not replace the notochord with a vertebral column during development. Lampreys notochord is surrounded by a cartilaginous structure called an arculia.
OBTAINING NUTRIENTS
Agnathans lack hinged upper and lower jaws and instead have unhinged circular mouths. Lampreys are parasitic and attach their sucker-like mouth to a fish and use their sharp teeth to rub at the prey's flesh. Hag fish are scavengers that feed off dead and wounded organisms in the ocean. They have a ring of tentacles surrounding their mouth that aid in obtaining food. Hagfish can twist their bodies into a knot to gain mechanical advantage while feeding on prey, and can even eat carcasses from the inside out. All agnathans digest the blood they take from other fish directly in the intestines, because they do not have stomachs. Digestion and absorption of nutrients occurs in the intestines. Agnathans excrete enzymes near the mouth cavity in order to break down the prey’s blood, preventing it from clotting.
Agnathans lack hinged upper and lower jaws and instead have unhinged circular mouths. Lampreys are parasitic and attach their sucker-like mouth to a fish and use their sharp teeth to rub at the prey's flesh. Hag fish are scavengers that feed off dead and wounded organisms in the ocean. They have a ring of tentacles surrounding their mouth that aid in obtaining food. Hagfish can twist their bodies into a knot to gain mechanical advantage while feeding on prey, and can even eat carcasses from the inside out. All agnathans digest the blood they take from other fish directly in the intestines, because they do not have stomachs. Digestion and absorption of nutrients occurs in the intestines. Agnathans excrete enzymes near the mouth cavity in order to break down the prey’s blood, preventing it from clotting.
RESPIRATION
Agnathans have seven pairs of gills and pouches located on the sides of their anterior end. They respire by pumping water in and out of the gill pouches. In some species, the gills open to the surface through separate pores. However, in others, the gills open to a common duct which in turn opens to the surface through a single pore. Agnathans have a single nostril at the anterior end. Water enters through the nostril and passes by a nasopharyngeal duct to the pharynx and gills. (Hag fish) Agnathans use their internal gills for gas exchange. It pulls water through its pharynx, gills, and into the gill pouches. Once the gases are exchanged, the water exits the pouches through the external gill slits. While feeding, gas exchange occurs through the external gill slits, forcing water to exit and enter through the gill slits so the agnathan can breathe.
Agnathans have seven pairs of gills and pouches located on the sides of their anterior end. They respire by pumping water in and out of the gill pouches. In some species, the gills open to the surface through separate pores. However, in others, the gills open to a common duct which in turn opens to the surface through a single pore. Agnathans have a single nostril at the anterior end. Water enters through the nostril and passes by a nasopharyngeal duct to the pharynx and gills. (Hag fish) Agnathans use their internal gills for gas exchange. It pulls water through its pharynx, gills, and into the gill pouches. Once the gases are exchanged, the water exits the pouches through the external gill slits. While feeding, gas exchange occurs through the external gill slits, forcing water to exit and enter through the gill slits so the agnathan can breathe.
CIRCULATION
Agnathans have a closed circulatory system with a two chambered heart, a single loop and blood vessels. The oxygen enters through the gills and travels through the heart to be pumped into the body capillaries, where the oxygenated blood spreads around the body. The de-oxygenated blood travels back up to the gills where oxygen travels back into. Blood is pumped through the ventral aorta all the way to the capillaries which are in the gills, where the blood becomes oxygenated.
Agnathans have a closed circulatory system with a two chambered heart, a single loop and blood vessels. The oxygen enters through the gills and travels through the heart to be pumped into the body capillaries, where the oxygenated blood spreads around the body. The de-oxygenated blood travels back up to the gills where oxygen travels back into. Blood is pumped through the ventral aorta all the way to the capillaries which are in the gills, where the blood becomes oxygenated.
EXCRETION
Agnatha excrete using a propulsion system called the anal ejector. Their kidneys not only send the waste out of their body through the anus, but also play a big role in keeping the amount of salt regulated in lampreys. Lampreys excrete waste through its cloaca near the caudal fin. Urine is excreted after passing through the kidney and out the cloaca.
Agnatha excrete using a propulsion system called the anal ejector. Their kidneys not only send the waste out of their body through the anus, but also play a big role in keeping the amount of salt regulated in lampreys. Lampreys excrete waste through its cloaca near the caudal fin. Urine is excreted after passing through the kidney and out the cloaca.
RESPONSE
Agnathans lack nervous systems and have poorly-developed brains. However, lamprey have large well-developed eyes, and hagfish have light-detecting sensors scattered around their bodies.
Agnathans lack nervous systems and have poorly-developed brains. However, lamprey have large well-developed eyes, and hagfish have light-detecting sensors scattered around their bodies.
REPRODUCTION
Agnathans reproduce sexually through external fertilization. There is no parental care. Hagfish species are hermaphrodites, but lampreys have separate sexes. Lamprey reproduce in freshwater riverbeds, working in pairs to build a nest and bury the eggs an inch beneath the sediment. Hatchlings go through four years of larval development before becoming adults. Lampreys only breed once in their lifetime and die shortly after.
Agnathans reproduce sexually through external fertilization. There is no parental care. Hagfish species are hermaphrodites, but lampreys have separate sexes. Lamprey reproduce in freshwater riverbeds, working in pairs to build a nest and bury the eggs an inch beneath the sediment. Hatchlings go through four years of larval development before becoming adults. Lampreys only breed once in their lifetime and die shortly after.