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Adam Richter

Chapter 34 - Introduction Deuterostomes: • largest-bodied • most morphologically complex of all animals • range from sea stars to fish to wildebeests • important in natural and human economies • key predators and herbivores in most marine and terrestrial habitats • always at the top of the food chain • humans rely on deuterostomes (vertebrates or animals with backbone) for food and power • humans are deuterostomes 34.1 An Overview of Deuterostome Evolution • 4 phyla of deuterostomes: 1) Echinodermata (sea stars and sea urchins) 2) Hemichordata or “acorn worms” (burrow in marine sands or muds and make their living by deposit feeding or suspension feeding) 3) Xenoturbellida (were once recognized as distinct phylum) 4) Chordata (vertebrates) Vertebrates • sharks, boney fishes, amphibians, reptiles (including birds), and mammals • animals that are not vertebrates are known as invertebrates (echinoderms, hemichordates, Xenoturbella) Deuterstomes • all undergo early embryonic development in a similar way • when a humpback whale, sea urchin, or human is just beginning to grow, cleavage is radial, the gut starts developing from posterior to anterior- anus first and mouth second- and a coelom (if present) develops from outpocketings of mesoderm • although they share features of embryonic development, their adult body plans and their feeding methods, modes of locomotion, and means of reproduction are highly diverse What is an echinoderm? • All deuterostomes are considered bilaterians because they evolved from a common ancestor that was bilaterally symmetric • adult echinoderms have bodies with five-sided radial symmetry (evolution of echinoderms), called pentaradial symmetry- even though both their larvae and their ancestors are bilaterally symmetric • radially symmetric animals do not have well developed heads and posterior regions • adult echinoderms are capable of movement- they can move in all directions equally instead of only headfirst • another echinoderm evolution was the origin of a unique morphological feature: a series of branching, fluid-filled tubes and chambers called the water vascular system -one of the tubes is open to the exterior where it meets the body wall, so seawater can flow into and out of the system -inside, fluid move via the beating of cilia that line the interior of the tubes and chambers -water vascular system forms a sophisticated hydrostatic skeleton -tube feet are elongated, fluid-filled structures -podia are sections of the tube feet that project outside of the body and make contact with the substrate -as podia extend and contract, they alternately grab and release substrate.As a result the individuals move -endoskeleton: hard, supportive structure inside a thin layer of epidermal tissue -as individual develops, cells secrete plates of calcium carbonate inside the skin -plates may remain independent and result in a flexible structure or fuse into a rigid case -along with radial symmetry and the water vascular system, this type of endoskeleton is a synapmorphy (monophyletic group) ◦ 2 other phyla form a monophyletic group with echinoderms : Xenoturbellida and Hemichordata -the Xenoturbellida (“strange flatworms”) have extremely simple, wormlike body plans -no gut, coleom, or brain -make living by absorbing nutrients in aquatic sediments -the hemichordata got their “half-chordates” name because of their unusual feature found in chordates – openings into the throat called pharyngeal gill slits -suspension feeders -live buried in muddy habitats on the ocean floor -pharyngeal gill slits function in feeding and gas exchange -water enters mouth, flows through structures where oxygen and food particles are extracted, and exits through pharyngeal gill slits. -not members of phylum chordata because they lack several defining features shared by chordates What is a Chordate? • Defined by the presence of four morphological features: 1) pharyngeal gill slits 2) stiff and supportive but flexible rod called notochord, which runs the length of the body 3) a bundle of nerve cells that runs the length of the body and forms a dorsal hallow nerve cord 4) a muscular, post-anal tail- meaning a tail that contains muscle and extends past the anus • 3 major lineages (subphyla) 1) urochordates (tunicates) -pharyngeal slits are present in both larvae and adults and function in both feeding and gas exchange just like hemichordates -the notochord, dorsal hallow nerve chord, and tail are only present in the larvae -results in swimming movements -as they float, they swim to new habitats where food is more abundant -urochordates underline the conclusion about chordate evolution • the 4 features that distinguished the group enabled new types of feeding and movement • pharyngeal gill slits function in suspense feeding in the adult • notochord functions as endoskeleton in the larva, while nerves in the dorsal cord move muscles in the tail that make swimming movements possible 2) cephalochordates (lancelets) -small, mobile suspension feeders that look like fish -adults live in ocean-bottoms in sand and suspension feed using pharyngeal gill slits -have notochord that stiffens their bodies, so that muscle contractions result in fishlike movement when they swim during dispersal or mating 3) vertebrates -sharks, several lineages of fish, amphibians, reptiles (birds), and mammals -dorsal hallow nerve cord is in spinal cord -pharyngeal pouches are present in all vertebrate embryos -in aquatic: creases between pouches open into gill slits and develop into gas exchange organ- the gills -in terrestrial: gill slits do not develop after the pharyngeal pouches form -a notochord appears in all vertebrate embryos -helps to organize body plan -although notochord disappears, cells in somite later differentiate into the vertebrae, ribs, and skeletal muscles of the back, body wall and limbs -notochord is instrumental in the development of the trait that gave vertebrates their name What is a Vertebrate? – monophyletic group distinguished by 2 traits: a column of cartilaginous or bony structures, called vertebrae, that form along the dorsal sides of most species, and a cranium, or skull- a bony, cartilaginous, or fibrous case that encloses the brain – vertebral column is important because it protects the spinal cord – cranium is important because it protects brain along with sensory organs such as eyes – vertebrates are active predators and herbivores that make rapid movements with aid of exoskeleton – coordinated movements are possible because vertebrates have large brains divided into 3 regions: 1) forebrain, housing the sense of smell -large structure called the cerebrum 2) midbrain, associated with vision 3) hindbrain, responsible for balance and hearing -enlarged regions called cerebellum and medulla oblongata 55.1 What is Biodiversity? Biodiversity can be measured and analyzed at three levels 1. GENETIC DIVERSITY- total genetic information contained within all individuals of a species and is measured as the number and relative frequency of all alleles present in a species -everywhere around you, from apples in store, to variation on colouration, singing ability of sparrows 2. SPECIES DIVERSITY- is based on variety of species on earth -taxonomic diversity and document by estimating phylogenies 3. ECOSYSTEM DIVERSITY- is the variety of biotic communities in a region along with abiotic components, such as soil, water, and nutrients -more difficult to define and measure than genetic diversity or species diversity, because ecosystems do not have sharp boundaries -areas around estuaries have high ecosystem diversity due to the combination of stream, wetland, intertidal, neritic, and upland habitats -when an estuary is dredged or filled, biodiversity is affected at all 3 levels: genetic and species diversity change due to the different numbers and types of individuals present, and ecosystem diversity is altered due to the change in abiotic conditions -biodiversity is dynamic -mutations that create new alleles increase genetic diversity; natural selection, genetic drift, and gene flow may eliminate certain alleles or change their frequency, leading to increase/decrease in overall genetic diversity -speciation increases genetic diversity; extinction decreases it -changes in climate or other physical conditions can result in formation of new ecosystems -disturbances such as volcanic er
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