15.+chordata+-+agnatha

Emmanuel Manolios

Pacific Hagfish chordata - agnatha: Picture of a hagfish on the seafloor in southern California (10) >> **Phylum **: Chordata >> **Class **: Myxini >> **Order **: Myxiniformes >> **Family **: Myxinidae >> **Genus **: Eptatretus >> **Species **: stoutii (Pacific hagfish) The Pacific Hagfish finds itself at the center of an eel-fishing industry that began in the 80s with Pacific Northwestern fishermen in Oregon starting to diversify the species they catch in order to stay competitive. Over a hundred thousand pounds of eel are caught each year, including the thick amounts of slime they secrete to deter predators that made the unfortunate choice of ingesting them. The eels are most popular in Korea, where millions of pounds of eel meat are consumed and the leather of which is used in such products as wallets and clothing items at regular department stores. Hunting in general has put the species at risk for extinction as of late. (12)
 * 1) Classification/Diagnostic characteristic
 * 2)  Chordataare one of the three major clades of living deuterostomes, along with Echinoderms and Hemichordates. ( Textbook page 483)
 * 3)  Chordataare broken up into three principal chordate clades: the cephalochordates, urochordates, and vertebrates ( Textbook page 485)
 * 4) They are able to survive for a long time without food. (2)
 * 5) The full classification for the pacific hagfish: (2)
 * 6) **Kingdom **: Animalia
 * 1) The hagfish's body is cylindrical and elongated (5)
 * 2) Hagfish lack scales, paired fins, a stomach, and jaws (5)
 * 3) Hagfish have eye spots that are sensitive to light (7)
 * 4) They are up to 25 inches long (64 cm).
 * 5) Relationship to humans

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 * 1) Habitat and niche
 * 2) Chordata live in both salt and fresh water (Textbook page 488)
 * 3) Hagfish that live in the ocean are bottom dwellers - they stay on the ocean floor. They can be found from 10 meters below sea level in high latitudes to 1300 meters below sea level near the equator (Britannica)
 * 4) They are found in both the Northern Hemisphere and the Southern Hemisphere and live in cold ocean waters (Wildlife Journal Junior)
 * 5) They are found in the Eastern North Pacific and it is known to be abundant across its distribution range. It is known to be most abundant off the coast of Northern California. Their population is decreasing.(Wildlife Journal Junior)
 * 6) Predator avoidance
 * 7) Hagfish, along with many other agnathas, hide in order to avoid predators (Textbook page 487)
 * 8) Hagfish can secrete a thick slime to clog the gills of would-be predators, choking them and killing them before they themselves are eaten (7)
 * 9) Hagfish themselves will die if they are left sitting in their own slime. this slime is secreted out of about 90-200 slime pores along the side of the body when the fish are stressed or scared (2)
 * 10) Hagfish also bite predators, protecting themselves from harm (2)
 * 11) Hagfish have been known to use slime to attack other predators, and allow them to escape to safety. (7)
 * 12) Nutrient acquisition
 * 13)  Some types of agnatha suck on their food in order to digest it, such as hagfish ( Textbook page 487).
 * 14) Other types, such as sea lampreys, attach themselves to a livingfish, and slowly suck blood and flesh (Textbook page 487).
 * 15) Interestingly enough, some types of lampreys do not eat as adults, and instead survive a few weeks with the sole goal of breeding (Textbook page 488)
 * 16) To find food, some use four pairs of thin sensory tentacles that surround their mouth. (2)
 * 17) They use their "rasping tongue" to carry food into their funnel-shaped mouth. (2)
 * 18) Hagfish locate their food by smell. ( [])
 * 19) Pacific Hagfish feed mainly on small marine invertibrates and carrion [|2]
 * 20) Reproduction and life cycle
 * 21) Hagfishes have direct development, and can actually change sex each year (Textbook page 488)
 * 22) Lampreys go through a complete metamorphosis from filter-feeding larvae known as ammocoetes (Textbook page 488)
 * 23) Although obtaining data about hagfish reproduction can be difficult due to embryo inaccessibility, new data finds that Atlantic hagfish may have seasonal reproductive cycles. (5)
 * 24) Growth and development
 * 25) All chordata develop a dorsal hollow nerve cord, a tail, and a dorsal supporting rod called the notochord (Textbook page 486)
 * 26) Chordata agathaare jawless fish that don't have paired fins or a stomach. All chordata have a notochord which is a flexible rod-like chord which supports the body. Most chordataagatha have skeletons made of cartlige, pineal eyes, and gill pockets. (11)
 * 27) Integument
 * 28) They are long and tubular in shape, resembling an eel. (1)
 * 29) They are cartilaginous fish that have a flexible skeleton. (1)
 * 30) Pacific hagfish have no true fins or true jaws. Their mouth is a ring of short tentacles.(1)
 * 31) Skin pores on both sides of their body is run the length of their degenerate lateral line. (1)
 * 32) Two teeth like structures that are made of keratin are present. (12)
 * 33) A skull made of cartilage is present but there is no vertebrae. (12)
 * 34) Movement
 * 35) Contain a tail (Textbook page 486)
 * 36) Some types of agnatha have a vertebrae, while others do not (Textbook page 487)
 * 37) swimming is called "snake-like"
 * 38) they pass a wave, bending their body down to propel themselves forward
 * 39) they can reverse this wave and movement to move backwards too
 * 40) it has fins that can be used to propel as well
 * 41) <span style="font-family: Helvetica,Arial,sans-serif; font-size: 13.6px;">anguilliform-mode swimmers
 * 1) Sensing the environment
 * 2) Hagfish have degenerated eyesight, and are often called blind eels as a result (Textbook page 487)
 * 3) Although blind, Hagfish have developed a strong sense of touch and smell. They primarily sense their environment by using their sensitive tentacles attached to their mouth that are used to find worms in the mud and sand. Hagfish have also have developed surprising olfactory senses in a muscle that projects from its mouth. (9)
 * 4) Gas exchange
 * 5) Have gills (Textbook page 488)
 * 6) They also have a single nostril at the anterior end overlying the mouth. Some species contain gills that open to the surface through separate pores.
 * 7) Bucchal funnel is located at the front of the head and are a key part of the respiratory system and ultimately gas exchange.
 * 8) Waste removal
 * 9) Contain an anus (Textbook page 486)
 * 10) Often times agnatha do not contain a stomach (Textbook page 487)
 * 11) The respiratory system and digestive system are interrelated systems; they depend on one another to eliminate waste.
 * 12) Environmental physiology (temperature, water and salt regulation)
 * 13) Are believed to have evolved in an estuarine environment (which is where fresh water meets salt water) (487)
 * 14) Internal circulation
 * 15) Have at least one heart (Textbook page 487)
 * 16) Hagfish are known to have four hearts, three of which are small accessory hearts (Textbook page 487)
 * 17) Chemical control (i.e. endocrine system)
 * 18) Can produce insulin and insulin like growth factors.
 * 19) Have a fairly extravagant endocrine system consisting of several organs including a liver, kidney(s), and gonads. (2)

Review Questions:

1. Based on the information above, how exactly are these organisms similar to humans? - Similarly to humans, these organisms have several organs that have the same function as those of humans including gonads, kidneys, and livers. Also, they produce similar hormones including insulin.

2. Given that they have degenerated eyesight, what might this tell you about the environment that these organisms live in? - Based on the fact that they no longer use their eyes, it is likely that they have allocated their energy use to other processes including homeostasis and reproduction.

3. Given the fact that hagfish have degenerated eyesight, what could this tell us about their evolution? This might suggest that they live in a dark environment where eyesight is not an advantageous trait, and mutations have clearly developed in favor of the lack of eyesight.

4. What are major sources of danger for hagfish? The eel fishing industry is a major source of danger for the hagfish, and has the potential to make the Pacific Hagfish go extinct.

5. What does the Pacific Hagfish generally eat, and how does it find its food? The Pacific Hagfish will usually eat any decaying animal or invertebrate on the sea floor. As a result of the Pacific Hagfish's lack of sight, it primarily uses its sense of smell to locate its food.

Citations: http://www.aquariumofpacific.org/onlinelearningcenter/species/pacific_hagfish (1) https://www.britannica.com/animal/agnathan (2) http://www.nhptv.org/wild/agnatha.asp (3) https://link.springer.com/chapter/10.1007/978-94-011-5834-3_26 (4) http://bio.rutgers.edu/~gb102/lab_3/403am-agnatha.html (5) [|https://www.nature.com/articles/srep00131 (6)] https://academic.oup.com/icb/article/45/1/158/604629 (7) https://www.smithsonianmag.com/science-nature/14-fun-facts-about-hagfish-77165589/ (8) https://www.wildlife.ca.gov/Conservation/Marine/NCCFRMP/Hagfish-ID (9) http://www.divebums.com/week/2007/Mar19-2007/hagfish_terry-strait.jpg (10) http://www.iucnredlist.org/details/196044/0 (11) http://theworldlink.com/fishermen-hook-overseas-hagfish-market/article_b5539028-c5dd-5951-9198-5066eb0ce04c.html (12) http://www.iucnredlist.org/details/196044/0 (13)