Introduction - Origin of Chordates PDF

1. Which group of animals is NOT included under the phylum Chordata? (living) a. Cephalochordates b. Urochordates c. Hemichordates d. Vertebrates Answer: c. Hemichordates 2. Why do we need to study chordates? Answer: -humans belong to this phylum -many chordates are constructed o...

1. Which group of animals is NOT included under the phylum Chordata? (living) a. Cephalochordates b. Urochordates c. Hemichordates d. Vertebrates Answer: c. Hemichordates 2. Why do we need to study chordates? Answer: -humans belong to this phylum -many chordates are constructed of hard parts that survive to yield a respectable history in the fossil record, which has made them especially useful in defining ideas about evolutionary processes. 3. In terms of embryonic development, how do protostomes and deuterostomes differ in the fate of blastopore? a. In protostomes, the blastophore becomes the anus, while in deuterostomes, it becomes the mouth. b. In protostomes, the blastophore becomes the mouth, while in deuterostomes, it becomes the anus c. Both protostomes and deuterostomes develop the mouth from the blastophore, but the process occurs at different stages. d. In both groups, the blastophore becomes the anus, but protostomes develop a secondary opening for the mouth. Answer: b. 4. Which of the following best describes the pattern of embryonic cleavage in protostomes compared to deuterostomes? a. Protostomes exhibit radial cleavage, while deuterostomes exhibit spiral cleavage. b. Both protostomes and deuterostomes exhibit radial cleavage, but protostomes have determinate development c. Protostomes exhibit spiral, determinate cleavage, while deuterostomes exhibit radial, indeterminate cleavage. d. Both protostomes and deuterostomes exhibit radial cleavage, but deuterostomes have determinate development Answer: c. 4. Considering coelom formation, how does the process differ between protostomes and deuterostomes? a. Protostomes form a coelom by splitting the mesoderm (schizocoely), while deuterostomes form it from archenteron pouches (enterocoely). b. Protostomes form a coelom by archenteron outpocketing (enterocoely), while deuterostomes form it by splitting the mesoderm (schizocoely). c. In both protostomes and deuterostomes, the coelom forms by enterocoely, but deuterostomes also develop a secondary ectodermal coelom. d. Both protostomes and deuterostomes form coeloms via schizocoely, but deuterostomes develop a larger, more complex coelom. Answer: a. 5. Which of the following best contrasts the skeletal system of protostomes and deuterostomes? a. Protostomes generally have a mesodermal skeleton, whereas deuterostomes have an ectodermal skeleton. b. Protostomes develop an endoskeleton from mesoderm, while deuterostomes develop an exoskeleton from ectoderm. c. Protostomes have an ectodermal-derived exoskeleton, whereas deuterostomes have a mesodermal-derived endoskeleton. d. Both protostomes and deuterostomes have a mesodermal skeleton, but deuterostomes have a more complex skeletal structure Answer: c. 6. What are the general characteristics of chordates? Answer: Notochord pharyngeal slits endostyle/thyroid gland Dorsal and tubular nerve cord Postanal tail 1. Notochord - Slender/elastic rod (can be flexed laterally but not collapsible) - Core of cells and fluid encased in a tough sheath of fibrous tissue - Hydrostatic organs with elastic properties - Replaced by vertebral column in bony fishes and terrestrial vertebrates (but still appear as embryonic structure) - Nucleus pulposus (notochord remnant in adult mammals) 7. Are the gills of a fish and amphibians function the same as the pharyngeal slits? Why? Answer: No, gills are used for respiration in water, but pharyngeal slits are openings only, often with no significant role in respiration. The first evolution of slits supported feeding and respiratory activity in primitive vertebrates having gills In gill-less primitive chordates, they primarily serve in feeding together with sets of cilia (for suspension feeders) but in embryos they play no respiratory role May appear in embryonic development and persist into adult stage, serving as exit channel of water (fish and amphibians) Embryonic pharyngeal slits normally never open and do not give rise to any adult derivative (vertebrates on land) 2. pharyngeal slits 8. Give two similarities of endostyle and thyroid gland. Answer: -arises embryologically from the floor of the pharynx -involved in iodine metabolism 9. Do all chordates have an endostyle/thyroid gland? Answer: -Yes, lamprey (jawless fish) have true endostyle when they are young larvae, and becomes a true thyroid gland in adults - Endostyle (urochordates, cephalochordates, larval lamprey) or thyroids (adult lamprey, all other vertebrates) 3. endostyle/ thyroid gland -filter feeding 10. Where do the dorsal hollow nerve cord is derived?? Answer: -ectoderm - The central nervous system of all animals is ectodermal in embryonic origin, but only in chordates does the nerve tube typically form by a distinctive embryonic process, namely, by invagination. 11. What organ system does the dorsal and tubular nerve cord give rise to? Answer: -CNS Kardong, K. (2012) 12. Give two differences of nerve tubes formation in chordates and non-chordates. Answer: -future nerve tube cells of the early chordate embryo gather dorsally into a thickened neural plate (neurulated nerve cord) within the surface of ectoderm at the back -hollow, surrounds the neurocoele (fluid-filled central canal) -in nonchordate, cells individually move inward to form basic CNS, below the gut, and solid Kardong, K. (2012) 4. Dorsal and tubular nerve cord 5. Postanal tail 13. What is the primary function of postanal tail? Answer: -locomotor -represents a posterior elongation of the body extending beyond the anus. 14. Which set of animals composes protochordates? Answer: -informal assemblage of animals -some of the earliest or “first”; hence, “proto-,” chordates. - collection of convenience where members share some or all five features of the fundamental chordate body plan. -immediate ancestors/primitive Protochordates -little record about chordate ancestors, living protochordates being studied for chordate origins. -anatomy is simple, and their phylogenetic position ancient. -For many years, scientists thought the first chordates resembled either baglike urochordates or wormlike enteropneusts, which then gave rise to streamlined, fish-shaped cephalochordates and from there, to true fishes (vertebrates) -However, it was long suspected that echinoderms and hemichordates were more closely related to each other than to other deuterostomes. -cephalochordates are now seen to be basal chordates and urochordates occupy a more derived position close to vertebrates (good model for first chordates) (based on anatomical evidence and molecular data) 15. Define patterning. Answer: -specifying the general regions of an embryo -determining which part of the embryo becomes dorsal (back) and which ventral (belly). -the actions of these gene sets is the reverse of all other animals including hemichordates. Ventral gene action in non-chordates is dorsal in chordates. This means that between hemichordates and chordates the body plan became flipped over or inverted Protochordates -marine animals that feed by means of cilia and mucus. 16. Differentiate protochordate larvae and adult Answer: -As larvae, they may be pelagic, residing in open water between the surface and the bottom. -Planktonic (free-floating; drift in water currents and tides than on their own efforts of long-distance swimming) -As adults, they are usually benthic, living on or within a bottom marine substrate. -Burrow into the substrate or are sessile and attached to it. -solitary, others are colonial and live together in associated groups. -dioecious (literally, two houses), with male and female gonads in separate individuals; others are monoecious (one house), with both male and female gonads in one individual. 1. Hemichordata -marine “worms” with apparent links to chordates on the one hand and to echinoderms on the other. - hemi- or half-chordates. 17. What hemichordate characteristic is synapomorphic with chordates Answer: - pharyngeal slits - lack a dorsal, hollow nerve cord (hollow collar cord resembles the chordate dorsal, hollow nerve tube, however is inverted in chordates) - Lack true postanal tail (consist of postanal appendage used to hold them in a burrow or tunnel, not for locomotion) - lack a notochord 1. Hemichordata -as larvae, some of these worms pass through a small planktonic stage called the tornaria larva which resembles the auricularia larva of echinoderms - equipped with ciliated bands on its surface and a simple gut (simple digestive system) - Morphological and molecular confirmed close relationship between hemichordates and echinoderms 18. True or False. Hemichordates are protostomes. Answer: - False, Hemichordates, like both echinoderms and chordates, are deuterostomes 19. True or False. Hemichordates are closer to chordates than echinoderms. Answer: - False, hemichordates exhibit affinities to chordates, larval (tornaria) and modern molecular evidence places hemichordates closer to echinoderms, even though echinoderms have obviously undergone extensive modifications (evolution of calcium carbonate surface plates) and radical makeover of their adult body plan (five-rayed symmetry in living forms) 20. Give the two taxon under hemichordates. Answer: - enteropneusts, burrowing forms, and the pterobranchs, usually sessile forms 1. Hemichordata a. Enteropneusts (burrowing forms) -acorn worms living both in shallow or deep waters -most live in mucus lined burrows and have a body with three regions—proboscis, collar, trunk— each with its own coelom -solitary; other species are suspension feeders -excretion through skin - contains glomerulus within the proboscis that filters the entering vascular fluid, yielding urine that is released into the proboscis coelom and eventually eliminated through the proboscis pore. - dorsal and ventral blood vessel (CS) - nervous system consists of diffuse network of nerve fibbers at the base of epidermis - gonads in trunks; dioecious; fertilization is external 1. Hemichordata b. Pterobranchs (sessile forms) -evolved from acorn worms -two genera -live in secreted tubes in oceanic waters -small and colonial, individual identity is often lost, each contributing individual to the colony is called zooid -Proboscis, collar, and trunk are present in each zooid (modified) -excretory organ include a glomerulus in the proboscis and perhaps a ciliated pair of collar ducts -simpler nervous system than acorn worms; tubular nerve cord is absent; collar ganglion (gives rise to several nerve branches) 21. Give the two taxon under hemichordates. Answer: - enteropneusts, burrowing forms, and the pterobranchs, usually sessile forms 2. Cephalochordata -lancelets/amphioxus resemble the earliest chordates (phylogenetic position) -body plan is dorsoventrally inverted compared to that of earlier deuterostomes including hemichordates. -living cephalochordates occur worldwide (warm tem perate and tropical seas) -chordate pattern that includes pharyngeal slits, tubular nerve cord, notochord, and postanal tail 22. What is the oldest likely cephalochordate from the Burgess Shales of Canada about the middle of the Cambrian? Answer: -Pikaia - has pair of sensory tentacles unlike the living form - Anatomically similar with living Branchiostoma (amphioxus) having noto- chord, presumptive pharyngeal slits, and chevron-shaped blocks of segmental body musculature. 2. Cephalochordata -simple anatomy -suspension feeders based on a pharyngeal filtering apparatus surrounded by an atrium -microorganisms and phytoplankton (diet) 22. What is the role of Hatschek’s pit or groove. Answer: -ciliated invagination that secretes mucus to help collect food particles -occurs in the roof of the buccal cavity, a similarity shared with the vertebrate pituitary gland, part of which also forms by invagination from the roof of the buccal cavity 23. What is the role of Buccal cirri?. Answer: -filament-like projections, act like a sieve that filters large particles from entering the buccal cavity 24. True or False. The blood of amphioxus is color blue. Answer: -The blood of amphioxus is a colorless plasma lacking blood cells and lacking oxygen- carrying pigments. 25. True or False. Amphioxus has five hearts. Answer: -False, no heart 2. Cephalochordata -endostyle of amphioxus collects iodine as does the thyroid gland, the pharyngeal endocrine gland of vertebrates -midgut cecum, a forward extension of the gut, is thought by some to be a forerunner of the liver (because of its position and blood supply) and of the pancreas (because cells in its walls secrete digestive enzymes). - closed-type of circulatory system - no specialized heart, blood is propelled by pulsation of several blood vessels (hepatic vein, ventral aorta (endostylar artery), bulbilli, and others) - Simple excretory system composed of paired nephridia consisting clusters of podocytes which eliminates metabolic wastes removed from the blood and flushed away by the stream of water passing through the atrium - Larval stage is planktonic (75 to over 200 days); adults are good swimmer - Larva is asymmetrical in head and pharynx - No true brain 3. Urochordates -tunicates or sea squirts (due to flexible outer covering called tunic/test which is a key feature) -tail backstring referring to the notochord -generally show all five shared derived chordate characteristics (at some point in life history) -proper chordates -specialist at feeding on suspended matter, especially very tiny particulate plankton (filter-feeders) -marine a. Ascidiacea – sessile as adults, swimming larvae b. Larvacea – permanently pelagic and drift in the plankton, unattached to any fixed substrate. c. Thalicea – same with Larvacea 26. True or False. Ascidiacea/ascidians/sea squirts are marine animals that are sessile throughout their life. Answer: -False, Adults are sessile, but larvae are planktonic. 27. True or False. Ascidiacea/ascidians/sea squirts’ larval stage exhibits all five chordate characteristics. Answer: -True, adults are simpler -small pharynx bears slits in the tadpole of colonial species -tubular nerve cord extends into a tail supported internally by a turgid notochord. -Vacuolated cells are absent from the ascidian notochord (no coelom), only rigid and tubular (composed of a single layer of epithelial cells covered externally by a circumferential sheath of collagen fibers) -postanal tail is present (twisted or rotated about 90° to the body) 3. Urochordates a. Ascidiacea Larva/ascidian tadpole - Does not feed during its short sojourn (short stay) of a few days as a free- living member of the plankton, but it disperses to and selects the site at which it will take up permanent residence as an adult - adhesive papillae (behind the tunic, epidermis at the anterior end) attaches the larva to substrate at the end of its planktonic stage - CNS subdivided into: (1) sensory vesicle (for orientation) and (2) visceral ganglion (send nerves to various parts of the body), both of which form a rudimentary brain, and (3) the dorsal, hollow nerve cord extending into the tail. 27. True or False. Ascidiacea/ascidians/sea squirts’ larval stage exhibits all five chordate characteristics. Answer: -True, adults are simpler -small pharynx bears slits in the tadpole of colonial species -tubular nerve cord extends into a tail supported internally by a turgid notochord. -Vacuolated cells are absent from the ascidian notochord (no coelom), only rigid and tubular (composed of a single layer of epithelial cells covered externally by a circumferential sheath of collagen fibers) -postanal tail is present (twisted or rotated about 90° to the body) 3. Urochordates Metamorphosis - planktonic stage, the ascidian larva attaches to a surface, usually in a dark area, and begins metamorphosis into a young adult. - Within minutes of attachment, the tail, including the notochord and associated structures, is drawn into the body - notochord becomes limp, and over the next few days, the notochord, dorsal nerve cord, and tail muscles are absorbed and repurposed for the growing juvenile - outer tunic layer, sensory vesicle, and visceral ganglion are also lost. - pharynx, enlarges and becomes highly modified, with its slits multiplying and forming smaller openings called stigmata. - development of the branchial basket, a key feature of the adult sea squirt. 3. Urochordates Adult - tunic, composed of a unique protein, tunicin, and a polysaccharide similar to plant cellulose, forms the body wall of an ascidian adult - The tunic attaches the base of the animal to a secure substrate - heart pumps blood through the body, reversing direction every few minutes. Unlike vertebrates, blood vessels lack an endothelium and are actually connective tissue spaces (hemocoels). - nervous system consists of a cerebral ganglion (like a brain) between the siphons, with nerves extending to various organs. - Contractions of smooth muscle bands allow the sea squirt to change shape and size, expelling water through the siphons when disturbed (derived its name “sea squirts”) - Hermaphrodites with both sexes in one individual, but self-fertilization is rare. 28. True or False. Ascidiacea/ascidians/sea squirts only reproduces asexually -False, Solitary ascidians reproduce sexually, while colonial ones can reproduce both sexually and asexually, often through budding, allowing rapid propagation and survival in adverse conditions. 3. Urochordates b. Larvacea (Appendicularia) - Tiny marine animals, few millimeters in length - Planktonic - retain larval characteristics into adulthood hence called larvacea - Unlike ascidians, larvaceans construct an external feeding apparatus, or "house," made of gelatinous material. This house contains screens and filters that trap food particles from the water as the larvacean's tail creates a current. If the filters clog, the larvacean abandons the house and quickly builds a new one. 29. True or False. Larvacea builds a house for its body protection -False, not part of its pharynx as in other urochordates. - holds the feeding screens and filters, and forms the channels through which streams of water carry suspended food particles - If the filters clog, the larvacean abandons the house and quickly builds a new one. - Their ability to filter ultraplankton, tiny organisms too small for other suspension feeders, gives them a competitive advantage. 30. True or False. All Larvacea species are dioecious -False, most of these are protandrous; that is, sperm and eggs are produced by the same gonad (of the same individual) but at different times during its life. -Maturation is so rapid that within 24 to 48 hours of fertilization, miniature larvaceans secrete a house and are set up for feeding 3. Urochordates b. Larvacea (Appendicularia) - Its trunk holds its major organs, though these vary across the three families of Larvacea. - digestive system typically includes a U-shaped tube and a mucus-producing endostyle. - blood circulates through simple sinuses, driven by a single heart and tail movement. 3. Urochordates c. Thaliacea -like larvaceans, are free-living, pelagic urochordates. -However, unlike larvaceans, they are thought to be derived from adult ascidians rather than from the tadpole stage. - have a few pharyngeal slits and use cilia, mucus, and a branchial basket for feeding, though the details are unclear. -Some species resemble colonial ascidians, with incurrent and excurrent siphons at opposite ends of the body. -They possess muscle bands that contract to expel water, creating a jet propulsion system for movement. Protochordates -encompassing hemichordates, cephalochordates, and urochordates - exhibit some or all of the five defining characteristics of the phylum Chordata: notochord, pharyngeal slits, endostyle or thyroid gland, dorsal hollow nerve cord, and postanal tail. - features may manifest at different stages of their life cycle. - benthic adult form and a planktonic larval stage - feed on suspended particles (captured by cilia-driven water currents and collected on mucous sheets before being directed to the gut) - Has long evolutionary history, preceding vertebrates, hence, evolutionary relationships have been studied extensively Chordate Origins The origins of chordates have been a subject of considerable debate due to the scarcity of fossils and the highly derived nature of modern invertebrates. 1. Chordates from Annelids and Arthropods -Geoffroy Saint-Hillaire first suggested in 1822 that the chordate body plan could be derived from an inverted arthropod -body segmentation, brain regionalization, and the positioning of the nerve cord (similarities) -solid nerve cord in annelids and arthropods compared to the hollow nerve cord in chordates, and the different embryological developments (differences) - have led to the rejection of this hypothesis Chordate Origins 2. Chordates from Echinoderms -more widely accepted hypothesis involves the origin of chordates from echinoderms. - William Garstang proposed the auricularian hypothesis, which suggests that chordate features first appeared in a larval form similar to the dipleurula larva of echinoderms. - characterized by bilateral symmetry, a simple gut, and cilia for locomotion, is thought to have evolved into the chordate body plan through elongation, the development of a notochord, and muscular locomotion. - Pharyngeal slits may have evolved to support suspension feeding. - lack of direct evidence for such a transformation and the difficulties in reconciling it with modern molecular phylogenetic data. - the reversal of dorsoventral patterning in chordates compared to other bilaterians, including echinoderms, complicates this scenario Vertebrate -proper chordates, possess the five general characteristics -live in freshwater, marine, and terrestrial, aerial, vast array of lifestyles -diversity might be attributed from opportunity - a time when few large predators existed 30. What are the two innovations present only in vertebrates Answer: Vertebral column and the cranium Innovations 1. Vertebral Column - composed of vertebrae, a series of separate bones or cartilage blocks firmly joined as a backbone that defines the major body axis. - intervertebral disks or bodies (thin compression pads squeezed between successive vertebrae) - A typical vertebra consists of a solid cylindrical body, or centrum, that often encloses the notochord, a dorsal neural arch enclosing the spinal cord, and a ventral hemal arch enclosing blood vessels - earliest vertebrates (Haikouella, Haikouichthys) relied upon a strengthened notochord to meet mechanical demands of body support and locomotion and rudimentary vertebrae - In these and other early fishes, the vertebral elements rode upon or surrounded a notochord that continued to serve as the major structural component of the animal’s body. -In later fishes and terrestrial vertebrates, successive vertebrae take over the functions of body support and movement. As the role of the vertebral column enlarged, that of the notochord in the adult declined. -In adults of most advanced vertebrates, the embryonic notochord disappears, although in mammals, it persists only as a small, springy, gel-like core within each intervertebral disk called the nucleus pulposus. Innovations 1. Vertebral Column Innovations 2. Head - cranium/skull (craniates) - cranium is a composite structure of bone and/or cartilage that supports sensory organs in the head and encases or partially encases the brain 30. What does cephalization mean? Answer: -Cephalization refers to the anterior clustering of specialized sensory organs such as paired eyes, ears, nose, and other sensory receptors. -The anterior part of the neural tube, which services these sense organs, enlarges to form a distinct brain that bulges, suggestive of forebrain, midbrain, and hindbrain. Innovations 2. Head - Vertebrate evolution has been characterized by a fresh and vast array of cranial structures that collectively form the head. - currently no better diagnostic vertebrate features than the presence of neural crest cells and epidermal placodes, both embryonic features found only in vertebrates. - While these cannot be directly observed in fossils, their adult derivatives can be identified. Origin of Vertebrates - origin and early evolution of vertebrates took place in marine waters; however, at one time, fossil and physiological evidence seemed to point to a freshwater origin