chodates..............................pptx
- 1. CHORDATES
- 2. Phylum Chordata • The chordates are a group of particular interest to us as we belong to it, being members of the subphylum Vertebrata. • The chordates include all of the vertebrates/craniata (fish, amphibians, reptiles, mammals and birds), but also two/3 non-vertebrate subphyla: the Urochordata and the Cephalochordata. • The chordates were in the 19th century considered to have been derived from protostome ancestors (the annelid, mollusc, arthropod group). • However, a better understanding of embryology shows that chordates are deuterostomes and the invertebrates they are most closely related to are the Echinodermata (sea stars, sand dollars, sea urchins) and the Hemichordata (acorn worms).
- 3. Protostomes and Deuterostomes • Within the eucoelomates there are two major evolutionary lineages that split early in the history of animals and follow quite different developmental pathways. These are the protostomes “mouth first” and deuterostomes “mouth second”.
- 4. Protostomes and deuterostomes • The differences in development that distinguish the protostomes and deuterostomes include: • Whether cleavage of cells in the early zygote is spiral or radial. • Whether or not, if the early blastomere is separated, each cell can develop into a normal larva or not. • Whether the blastopore ultimately forms the mouth or anus of the organism. • Whether or not the organism possesses a coelom and how that coelom is formed.
- 6. Characteristics of the Chordata • Chordates are: • bilaterally symmetrical • triploblastic • have a well developed coelom • have a complete digestive system
- 7. Germ layers of a triploblastic organism • Endoderm: innermost germ layer of an embryo. Forms the gut, liver, pancreas. • Ectoderm: Outer layer of cells in early embryo. Surrounds the blastocoel. Forms outer epithelium of body and nervous system. • Mesoderm: Third germ layer formed in gastrula between ectoderm and endoderm. The coelom forms in the mesoderm. Mesoderm gives rise to connective tissue, muscle, urogenital and vascular systems and peritoneum.
- 9. Coeloms • The coelom is a cavity entirely surrounded by mesoderm. • A coelom provides a tube-within-a-tube arrangement which has many advantages:
- 10. Advantages of a coelom • In mammals the pericardial, peritoneal, and pleural cavities are formed from the coelom. • Allows flexibility in arranging visceral organs • Permits greater size and complexity of internal organs as there is space for them to grow • Fluid-filled coelom can act as a hydrostatic skeleton • Cushions organs against impact • Allows organs to grow and move independently of your outer body wall.
- 11. Five distinctive characteristics of the chordates • Five distinctive characteristics separate the chordates from all other phyla: • Notochord • Single, dorsal, tubular nerve cord • Pharyngeal pouches or slits • Endostyle • Postanal tail • Not all of these characteristics are apparent in adult organisms and may appear only in the embryonic or larval stages.
- 12. Notochord • Notochord: the notochord is a flexible, rodlike structure. It extends the length of the body and is an anchor point for muscles. • The notochord bends without shortening so it permits the animal to undulate.
- 13. Figure 23.01
- 14. Notochord • In nonvertebrates and the jawless vertebrates the notochord is present throughout life. • However, in the jawed vertebrates it is replaced by the vertebral column; the remnants of the notochord being found in the intervertebral disks.
- 15. Single, dorsal, tubular nerve cord • In most invertebrates the nerve cord, if present, is ventral to the gut. • In chordates, in contrast, the nerve cord is dorsal to the gut and notochord. The nerve cord passes through the neural arches of the vertebrae, which protect it. • The nerve cord is enlarged in vertebrates into a brain, which is surrounded by a bony or cartilaginous cranium.
- 16. Pharyngeal pouches and slits • Pharyngeal slits occur in aquatic chordates and lead from the pharyngeal cavity to the outside. • The pharyngeal slits are used as a filter feeding device in protochordates (i.e., Urochordata (Tunicates)) and Cephalochordata (lancelets e.g. Amphioxus). • Water containing food is drawn in through the mouth by cilia and exits via the pharyngeal slits where the particles are trapped in mucus.
- 18. Pharyngeal pouches and slits • In vertebrates the pharyngeal arches have been modified into gills by the addition of a rich blood supply and thin gas permeable walls. • The contraction of muscles in the pharynx drive water through the gills.
- 19. Pharyngeal pouches and slits • In amniotes an opening may not form and rather than slits only grooves called pharyngeal pouches develop. • In tetrapods these pouches give rise during development to a variety of structures including the middle ear cavity, eustachian tube, and tonsils.
- 20. Endostyle or thyroid gland • The endostyle is found in protochordates and in lamprey larvae. It is located on the floor of the pharynx and secretes mucus, which is used to trap particles. • The endostyle works with the pharyngeal slits in filter feeding.
- 21. Endostyle or thyroid gland • Some cells in the endostyle secrete iodinated proteins and are homologous with the iodinated-hormone secreting thyroid gland, which is found in adult lampreys and vertebrates.
- 22. Postanal tail • The postanal tail, some musculataure and the notochord enable larval tunicates and amphioxus to swim. • The postanal tail evolved to allow organisms to swim and its efficiency has been enhanced by the addition of fins. The postanal tail is present only in vestigial form in humans (the coccyx) although tails as a whole are widespread among vertebrates.
- 24. Classification of the Chordata • There are three subphyla in the Chordata: • Subphylum Urochordata: tunicates • Subphylum Cephalochordata: lancelets • Subphylum Vertebrata: fish, amphibians, reptiles, birds, mammals, etc.
- 25. ORIGIN OF CHORDATES • It is believed that chordates originated from invertebrates. • However, it is difficult to determine from which invertebrate group of the chordate developed. It is almost constant that chordate ancestors weresoft bodied animals. Hence, they were not preserved as fossil. • Many theories have been put forward to explain the evolution of chordates, few of them are as follows
- 26. • COELENTERATE THEORY: According to this theory chordates developed from coelenterates. It is believed that radial symmetry coelenteron, cnidoblasts etc, disappeared and advanced characters developed to give rise the chordates. • This theory infers that chordates might have acquired higher characters independently. This theory is not acceptable. • Supporting Evidence • Both chordates and certain coelomates, like annelids, exhibit a segmented body plan. • The dorsal nerve cord in chordates is comparable to the ventral nerve cord in annelids. • Early developmental patterns, such as coelom formation, are similar. • Challenges: • The differences in the position of the nerve cord (dorsal in chordates, ventral in annelids) and the direction of the blood ORIGIN OF CHORDATES
- 27. • The Enteropneust (Hemichordate) Theory • This theory suggests that chordates evolved from hemichordates, a group of marine invertebrates that include the acorn worms. Hemichordates share some morphological features with chordates, such as a pharyngeal gill slits and a dorsal nerve cord in the collar region. • Supporting Evidence: • Hemichordates possess pharyngeal slits, which are also present in chordates. • The nerve cord in the collar region of hemichordates is dorsal, similar to the chordate nerve cord. • Molecular studies indicate a closer relationship between hemichordates and chordates. • Challenges: • Hemichordates lack a notochord and a post-anal tail, both of which are defining characteristics of chordates. • The overall body plan and development of hemichordates differ significantly from those of chordates. ORIGIN OF CHORDATES
- 28. • The Auricularian Hypothesis (Garstang’s Hypothesis) • Proposed by Walter Garstang in 1928, this theory suggests that chordates evolved through a process of paedomorphosis (retention of juvenile features in the adult stage) from an echinoderm-like ancestor. Garstang hypothesized that the chordate ancestor was a larval form of an echinoderm that became sexually mature without undergoing the usual adult transformation. • Supporting Evidence: • Echinoderm larvae (e.g., bipinnaria larvae) share some morphological similarities with the larvae of primitive chordates like tunicates. • Both echinoderms and chordates are deuterostomes, meaning they share a similar pattern of early embryonic development. • Challenges: • Echinoderms exhibit a radial symmetry as adults, whereas chordates exhibit bilateral symmetry throughout life. • The transition from a larval echinoderm to a chordate is complex and lacks direct fossil evidence. ORIGIN OF CHORDATES
- 29. • The Dipleurula Hypothesis • This theory proposes that chordates evolved from a dipleurula-like ancestor. Dipleurula is a hypothetical larval form that is believed to be a common ancestor of all deuterostomes, including echinoderms and chordates. This larva would have had a bilateral body plan with cilia for movement and feeding. • Supporting Evidence: • The bilateral symmetry of dipleurula-like larvae aligns with the symmetry seen in chordates. • The presence of similar larval forms in both echinoderms and hemichordates suggests a possible evolutionary link. • Challenges: • The dipleurula is a hypothetical organism with no direct fossil evidence. • The transition from a ciliated larva to a chordate with a notochord and a dorsal nerve cord is not fully explained. ORIGIN OF CHORDATES
- 30. • The Urochordate (Tunicate) Hypothesis • This theory suggests that chordates evolved from urochordates (tunicates), a group of marine invertebrates that possess a notochord, a dorsal nerve cord, and a tail in their larval stage, resembling the basic chordate body plan. • Supporting Evidence: • The larval stage of tunicates (ascidian tadpole) exhibits all the key chordate features: a notochord, dorsal nerve cord, and post-anal tail. • Molecular and genetic studies suggest a close relationship between tunicates and vertebrates, with tunicates being the closest living relatives of vertebrates. • Challenges: • Tunicates undergo a dramatic metamorphosis, during which most of their chordate features are lost, which complicates the understanding of how a chordate-like organism could evolve from a tunicate ancestor. • The adult body plan of tunicates is highly derived and does not resemble other chordates. ORIGIN OF CHORDATES
- 31. • The Cephalochordate (Lancelet) Hypothesis • This theory posits that chordates evolved from an ancestor similar to modern cephalochordates (lancelets). Cephalochordates exhibit all the key characteristics of chordates throughout their life, including a notochord, dorsal nerve cord, pharyngeal slits, and post-anal tail. • Supporting Evidence: • Cephalochordates possess a body plan that is remarkably similar to that of the hypothetical ancestral chordate. • Genetic and molecular evidence suggests that cephalochordates are closely related to vertebrates and other chordates. • Challenges: • Cephalochordates are specialized organisms, and there is debate about whether their body plan represents the primitive condition of chordates or is the result of secondary simplification. • Fossil evidence directly linking cephalochordates to early chordates is limited. ORIGIN OF CHORDATES
- 32. • The Echinoderm-Cephalochordate Hypothesis • This theory combines aspects of the Auricularian Hypothesis and the Cephalochordate Hypothesis. It suggests that chordates evolved from an ancestor that was intermediate between echinoderms and cephalochordates. The theory proposes that the common ancestor of chordates and echinoderms had a simple, bilateral larva that evolved into the complex chordate body plan. • Supporting Evidence: • Both echinoderms and chordates are deuterostomes, sharing similarities in embryonic development. • Some fossil evidence, such as early chordate-like fossils (e.g., Pikaia), shows a mix of features that could bridge the gap between echinoderms and chordates. • Challenges: • The fossil record is sparse and does not provide a clear lineage connecting echinoderms, cephalochordates, and other chordates. • The exact nature of the transition from a simple bilateral organism to a fully developed chordate remains speculative. ORIGIN OF CHORDATES
- 33. 12/03/2024 @ssemuyigacharles 33 Economic Importance of Chordates • A. Food Source: 1. Many chordates, such as fish and mammals, are harvested for human consumption, providing a significant source of protein and nutrients. 2. Aquaculture, or the farming of fish and other aquatic organisms, has become an increasingly important industry to meet the growing demand for seafood. • B. Biomedical Research: 1. Chordates, particularly mammals, are used extensively in biomedical research to study human health and disease. 2. Mice and rats, in particular, are commonly used as model organisms for studying genetics, physiology, and the development of new medical treatments. • C. Ecological Services: 1. Chordates play important roles in ecosystem functioning, including nutrient cycling, predator-prey dynamics, and maintaining biodiversity. 2. Birds, for example, are important pollinators and seed dispersers, while marine mammals such as whales contribute to nutrient cycling through their feces. • D. Recreation and Tourism: 1. Many chordates, such as birds and marine mammals, are popular attractions for ecotourism and recreational activities such as birdwatching, whale watching, and wildlife photography. 2. Ecotourism provides economic benefits to local communities and supports conservation efforts to protect natural habitats and endangered species.
- 34. SELF-ASSESSMENT QUESTIONS 1. Which of the following is the Class of the Jawless Fish? A. Chondrichthyes B. Chordata C. Osteichthyes D. Agnatha 2 Which of the following is not a feature of the Class Agnatha? A. External Fertilliation B. Ectothermic C.No Paired Limbs D.Has scales 3. Notochord is confined to proboscis in: A. Urochordata B. Hemichordata C. Cephalochordata D. Chordata 4. Chondrichthyes have a..... A. Closed circulatory system B. 3 chambered heart C. Clitellum D. Radial symentry E. All of the above 8. Which class would a frog belong to? A. Frogania B. Amphibian C. Agnatha D. Animmalia 9 Dry scaly skin, ectothermic, 2 Paris of legs, lungs, internal fertilization, leathery eggs with amniotic shell, and a 3.5 chambered heart are all properties of the class? A. Osteichthyes B. Agnatha C. Amphibian D. Reptiles 5. An example of an animal from the Class Agnatha is a... A. Red Trailed Fox B. Humanoid C. Rock Bass D. Lamprey 6. Which of the following is not an example of an animal from the Class Chondrichthyes? A. Ray B. Skate C. Sea Urchin D. Shark 7. What would a rainbow trout be an example of? A. Osteichthyes B. Agnatha C. Fishinidia D. Troutlopod E. None of The Above
- 35. • All chordates possess a notochord at some point in their life cycle. • Chordates are exclusively marine animals. • The notochord in chordates is a flexible, rod-like structure that supports the body. • All chordates are vertebrates. • The pharyngeal slits in chordates are involved in respiration or feeding. • In chordates, the dorsal nerve cord develops into the central nervous system. • Adult tunicates have all the characteristic features of chordates. • Chordates can be distinguished from other animals by the presence of a post-anal tail. • Lancelets are a type of chordate that have a vertebral column. • The endostyle, found in chordates, is involved in hormone production.
- 36. • 1.(D) 2.(E) 3.(B) 4.(A) 5 (D) 6. (C) 7.(A) 8.(B) 9.(D) . 1. Give the classification of Chordata. 2. Give the gearenal characters of the phylum chordate. 3. Describe the diagnostic characters of the phylum chordate and point out the main differences from that of nonchordate?
- 37. • 1. Which of the following is NOT a characteristic of chordates? - a) Notochord - b) Pharyngeal slits - c) Exoskeleton - d) Dorsal nerve cord 2. Which of the following animals is a chordate? - a) Jellyfish - b) Earthworm - c) Shark - d) Starfish 3. In which subphylum do vertebrates belong? - a) Cephalochordata - b) Urochordata - c) Vertebrata - d) Hemichordata 4. The pharyngeal slits of chordates are primarily used for what function in aquatic animals? - a) Feeding - b) Respiration - c) Reproduction - d) Excretion 5. Which chordate feature develops into the brain and spinal cord in vertebrates?* - a) Notochord - b) Pharyngeal slits - c) Dorsal nerve cord - d) Post-anal tail 6. What type of symmetry do chordates exhibit? - a) Radial symmetry - b) Bilateral symmetry - c) Asymmetry - d) Pentaradial symmetry 7. Which of the following is a feature shared by all chordates during at least some stage of their life? - a) Vertebral column - b) Notochord - c) Endoskeleton - d) Gills - 8. What does the term "Cephalochordata" refer to in the context of chordates? - a) Jawed vertebrates - b) Cartilaginous fish - c) Lancelets - d) Tunicates 9. In which of the following does the notochord persist throughout life? - a) Fish - b) Amphibians - c) Mammals - d) Lancelets 10. The endostyle in chordates is homologous to which gland in vertebrates? - a) Thyroid gland - b) Adrenal gland - c) Pituitary gland
- 38. • 1. Explain how the notochord differs from the vertebral column, and why both are essential in understanding chordate evolution. • 2. Why are some chordates classified as invertebrates, even though they possess a notochord? • 3. Discuss the significance of pharyngeal slits in the evolutionary history of chordates. • 4. How does the development of the dorsal nerve cord in chordates demonstrate the evolutionary advancement over non-chordates? • 5. What evolutionary advantage might a post-anal tail confer to chordates? • 6. Why do some chordates lose their notochord as they mature, while others retain it? • 7. How does the study of embryology support the classification of chordates? • 8. In what way is the classification of tunicates as chordates both obvious and misleading? • 9. Discuss the significance of the endostyle in the evolutionary link between chordates and other deuterostomes. • 10. Why might the presence of a notochord be considered more foundational to chordate identity than the presence of a vertebral column