Transcript CHAPTE 1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 11 Annelids and Allied Taxa 17-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics Diversity • Annelids exhibit segmentation or metamerism • Evolution of metamerism allowed much greater complexity in structure and function – Increased burrowing efficiency by permitting independent movement of segments – Evolution of a more sophisticated nervous system – Provided a safety factor • If one segment failed, others could still function 17-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics • Cleavage is spiral mosaic • Share a trochophore as the ancestral larval form • Segmented worms living in marine, freshwater, and moist terrestrial habitats • Include marine bristle worms, leeches, and earthworms, pogonophorans, and vestimentiferan worms 17-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Annelida Characteristics • About 15,000 species • 2/3 are the more obscure marine worms. • Segmentation – Body segments marked by circular grooves called annuli – Metamerism • Repetition of organs in segments called metameres or somites – Septa separate segments 17-5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Annelida • Setae – Tiny chitinous bristles called setae – Absent in leeches – Short setae anchor segments in earthworms • Prevent it from slipping backward – Long setae help aquatic worms swim • Polychaetes – Primarily marine and usually benthic • Oligochaetes and leeches – Freshwater or terrestrial soils – Many leeches are parasites 17-6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Annelida Body Plan – Head – Terminal portion bearing the anus is the pygidium – Head and pygidium are not considered metameres – New metameres form in front of the pygidium • Coelom – Peritoneum (mesodermal epithelium) lines body wall and forms dorsal and ventral mesenteries • Hydrostatic Skeleton – Except in leeches, coelom is filled with fluid and serves as a hydrostatic skeleton – Contraction of longitudinal muscles • Causes body to shorten and expand – Contraction of circular muscles • Causes body to narrow and lengthen 17-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Annelida Phylogeny • Traditionally, annelids are divided among 3 classes – Class Polychaeta – Class Oligochaeta – Class Hirudinida 17-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Polychaeta Diversity • • • • Largest class of annelids More than 10,000 species, mostly marine Vary from 1 mm to 3 meters long More specialization of sensory organs than in clitellates • Tolerate a wide range of salinity • Warmer regions have more freshwater polychaetes • Some live in crevices, others inhabit tubes, or are pelagic 17-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Class Polychaeta • Important part of marine food chains • Well-differentiated head with sense organs • Paired appendages called parapodia on most segments • No clitellum • Many setae arranged in bundles on parapodia • Sedentary polychaetes mainly tube-living • Clamworm Nereis is an example of a predatory polychaete with jaws on an eversible, muscular pharynx 17-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Siboglinidae (Pogonophorans) • Formerly members of phylum Pogonophora (beardworms) • Discovered in 1900 Characteristics • 150 species described • Most are small, less than 1 mm in diameter • Giant beardworms that live in deepwater hydrothermal vents are 3 m long and 5 cm in diameter 17-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Siboglinidae (Pogonophorans) Internal body • No mouth or digestive tract • Mode of digestion puzzling • Nutrients such as glucose and amino acids absorbed from seawater from a mutualistic relationship with chemoautrophic bacteria that oxidizes hydrogen sulfide • Trophosome, derived embryonically from midgut, houses the bacteria 17-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Clitellata • Class Oligochaeta and Class Hirudinida • Form reproductive structure called a clitellum – Ring of secretory cells found in a band around the body – Permanent in oligochaetes but visible only during reproductive season in leeches • Members are derived annelids that lack parapodia • Hermaphroditic (monoecious) animals that exhibit direct development • Young develop inside a cocoon secreted by the clitellum, and emerge as small worms 17-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Clitellata Class Oligochaeta • Diversity – – – – Over 3000 species Occur in habitats from soil to freshwater Few are marine or parasitic Nearly all bear setae • Fewer in number than in polychaetes • Form and Function – Sometimes called “night crawlers” – Burrow in moist rich soil and usually live in branched interconnected tunnels 17-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Setae Clade Clitellata – Bristlelike rods set in a sac and moved by tiny muscles – Project outward through small pores in cuticle – Aid anchoring by digging into walls of burrow • Nutrition – Scavengers, feeding on decayed organic matter, leaves, refuse, etc. – Food moistened by mouth and drawn in by a sucking action of muscular pharynx – Calcium in soil leads to high blood Ca+2 • Calciferous glands along the esophagus reduce calcium ion concentration in the blood 17-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Clitellata – Mate at night during warm, moist weather – Sperm from each worm are transported to the seminal receptacles of the other along seminal grooves – After mutual copulation, each worm secretes a mucus tube and chitinous band to form a cocoon – Young worms emerge from cocoon 17-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Clitellata • Class Hirudinida: leeches – Most freshwater, few marine or live in moist terrestrial environments – More common in the tropics temperate zones – Vary in color: black, brown, red, and olive green – Most are flattened – Some carnivores feeding on small invertebrates – Others are temporary or permanent parasites – Hermaphroditic – Form a clitellum during breeding season • Secretes a cocoon for reception of eggs 17-24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Echiura Diversity • Approximately 140 species of marine worms that burrow into mud or sand • Live in empty snail shells or sand-dollar tests, or rocky crevices • Found in all oceans • Length varies from a few millimeters to 40 or 50 cm 17-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Sipuncula Diversity • Approximately 250 species of benthic marine worms • Sedentary, living in burrows of mud or sand, snail shells, coral crevices, or among vegetation • More than ½ restricted to tropical zones • Some are tiny, slender worms, but most range from 3 to 10 cm in length • Some are known as “peanut worms” because when disturbed, they contract to a peanut shape 17-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17-30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ecdysozoans CHAPTER 12 18-31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diversity • Many protostomes possess a cuticle – Non-living outer layer secreted by epidermis • Cuticle restricts growth and must be molted via ecdysis • Members of Ecdysozoa molt cuticle as they grow • Regulation of molting achieved by the hormone ecdysone • This biological event used by scientists to group ecdysozoans in the same taxa 18-33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Diversity • About 25,000 species are described – As many as half a million may exist • Found in virtually all habitats in all biomes – Topsoil may contain billions per acre • Nematode parasites exist in nearly all animal and plant species 18-35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms • Free-living nematodes feed on bacteria, yeasts, fungal hyphae, and algae • Predatory nematodes eat rotifers, tardigrades, small annelids, and other nematodes • Important as food for mites, insects, larvae, and fungi • Caenorhabditis elegans is an important model for studies of genomics and cell development and differentiation 18-36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Form and Function • Distinguishing Characteristics – Cylindrical shape – Nonliving cuticle – Cuticle shed during juvenile growth stages • One of the characteristics used for placing the nematodes in the superphylum Ecdysozoa 18-37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms Representative Nematode Parasites • Some are parasites of humans – Most are tropical • Ascaris lumbricoides – Occurs in up to 25% of people in some areas of the southeastern U.S. – More than 1.27 billion affected worldwide – A female Ascaris may lay 200,000 eggs a day, which pass out in host’s feces – Embryos develop into juveniles in 2 weeks 18-39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms – Survive for long periods in soil – Host swallows embryonated eggs, juveniles hatch, and burrow through intestinal wall – Carried through the heart to the lungs, they break into alveoli and are carried up to tracheae – Coughed up and swallowed, they mature in the intestine after two months – They feed on intestinal contents and may block or perforate the intestines – Infection rates tend to be higher in children and males 18-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms • Hookworms – Anterior end of these small (9–11 mm) worms has a hooklike curve – Necator americanus, most common hookworm. – Sexes are separate – Large plates in mouth cut into intestinal mucosa and suck host’s blood – Pump through more blood than they digest • Heavy infections cause anemia – Eggs pass out in feces and juveniles hatch in soil – If human skin comes in contact with soil, infective juveniles burrow through skin to blood – Travel in blood to the lungs, are coughed up to be swallowed, and mature in the intestine 18-42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms • Trichina Worm – Trichinella spiralis causes a potentially lethal trichinosis – Adult worms burrow into intestinal mucosa and females directly produce juvenile worms – Juveniles penetrate blood vessels and circulate throughout the body to all tissues and spaces – Penetrate skeletal muscle cells, redirecting gene expression of the musculature • Cells lose striations and becomes a nurse cells to the parasite – When poorly cooked meat containing encysted juveniles is eaten, worms are liberated and mature in the intestine 18-44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms – Infect humans, hogs, rats, cats and dogs • Hogs can become infected eating uncooked scraps of infected meat or rats – Four other sibling species with variable distribution, freezing resistance, etc. – Heavy infections cause death 18-46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms • Pinworms – Most common parasite in the U.S. but causes little disease – Adults live in large intestine and cecum – Females, about 12 mm long, migrate to anal region at night and lay eggs, causing itching – Scratching the anal region contaminates hands and bedclothes 18-47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-48 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematoda: Roundworms • Filarial Worms – Eight species of filarial nematodes infect humans • Some cause serious diseases – Wucheria bancrofti and Brugia malayi live in lymphatic system • Cause inflammation and blockage of the lymphatics vessels • Carried by mosquitos • Elephantiasis is caused by repeated exposure – Swelling and growth of connective tissue causes enormous swelling of body parts – River blindness or onchocerciasis is carried by black flies and infects 37 million people in tropics – Dog heartworm, Dirofilaria immitis, is carried by mosquitoes and is the most common U.S. filarial worm 18-49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-50 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Nematomorpha Diversity • “Horsehair worms” resemble coarse hairs • Adult structures resemble those seen in nematodes: cuticle, epidermal cords, only longitudinal muscles, and a nervous system • Adults are free-living in moist habitats • Juveniles are parasites of arthropods 18-51 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-52 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Kinorhyncha Diversity • Kinorhynchs are usually under 1 mm long • About 179 species are known • Found worldwide, from intertidal areas to 6000 m deep • Most live in mud • Some have been found in algae, sponges, and other invertebrates 18-53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-54 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Priapulida Diversity • 16 species of marine worms occur in colder waters • Found from intertidal zones to deep ocean floors, several thousand meters deep • Some are tube dwellers and feed on detritus 18-55 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-56 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phylum Loricifera Diversity • Recently discovered (1983) in spaces between grains of marine gravel • 11 currently described species and 80 undescribed species • Widely distributed • Most species have been found in coarse sediments at depths of 300–450 m • One species was collected at 8000 m 18-57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Panarthropoda • Contains Arthropoda and two allied phyla, Onychophora and Tardigrada 18-59 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Panarthropoda Phylum Onychophora History and Diversity • About 70 living species of “velvet worms” • Range from 1.4 to 15 cm in length • Limited to moist, leafy rain forest habitat in tropical and subtropical regions • Changed little over 500 million years • Most are predaceous, some live in termite nests 18-60 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-61 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Clade Panarthropoda Phylum Tardigrada Diversity • Very small, less than 1 mm long • Most of the 300–400 known species known live in a water film around mosses and lichens – Few are marine • Cryptobiosis – Terrestrial tardigrades can suspend metabolism to survive harsh conditions – Tardigrades can dehydrate from 85% water to only 3% water • In this state they can resist extreme temperatures, ionizing radiation, oxygen deficiency, etc. for years – When water is available, they become metabolically active again 18-62 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18-63