19.4 Molluscs, Annelids, and Arthropods

Transcript 19.4 Molluscs, Annelids, and Arthropods

• • • • • • 19.1 Evolution of Animals

19.1.1 Explain how animals are distinguished from other groups of organisms. 19.1.2 Explain how the evolutionary tree of animals is constructed.

19.2 Introducing the Invertebrates

19.2.1 Describe the evolutionary trends among sponges, cnidarians, flatworms, and roundworms.

19.2.2 Give examples of flatworms and roundworms that adversely affect human health.

19.3 Protostomes and Deuterostomes Compared

19.3.1 Distinguish between protostomes and deuterostomes.

19.4 Molluscs, Annelids, and Arthropods

19.4.1 Recognize the common characteristics of molluscs, annelids, and arthropods.

19.4.2 Describe the defining characteristics of molluscs, annelids, and arthropods, and give examples of each.

19.4.3 Explain why arthropods are such a successful group.

19.5 Echinoderms and Chordates

19.5.1 Recognize the common characteristics of echinoderms and chordates.

19.5.2 Describe the defining characteristics of echinoderms.

19.5.3 Describe the defining characteristics of the invertebrate and vertebrate chordates.

19.5.4 Describe the defining characteristics of each group of vertebrates: fishes, amphibians, reptiles, and mammals.

19.6 Human Evolution

19.6.1 Explain how the evolutionary tree of primates is constructed.

19.6.2 Describe evolutionary trends among the hominins.

19.6.3 Summarize the two major hypotheses for the evolution of modern humans.

19.1 Evolution of animals

• • • • Animals are multicellular eukaryotes.

Like plants and fungi • • Animals are chemoheterotrophs.

Unlike autotrophic plants Like fungi but animals ingest food and digest internally while fungi digest food externally • • • Animals usually carry on sexual reproduction.

Begin life as a fertilized diploid egg Undergo developmental changes • Organism with specialized tissues Muscle and nerve tissue characterize animals.

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Ancestry of animals

 Colonial flagellate hypothesis • Animals descended from an ancestor that resembled a hollow spherical colony of flagellated cells.

• Implies radial symmetry preceded bilateral symmetry as the evolutionary tree of animals predicts

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Among protists, choanoflagellates most likely resemble the last unicellular ancestor of animals.

 Supported by molecular data

single cell Figure 19.3 Choanoflagellate

stalk

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Evolutionary tree of animals

 Based on molecular data and developmental stages  Trends • Multicellularity • • 2 or 3 true tissues associated with 2 germ layers in embryos Symmetry – radial vs. bilateral  Bilateral organisms with cephalization • • Protostome vs. deuterostome  Protostomes can be acoelomate, pseduocoelomates or coelomates.

 Deuterostomes are coelomates.

Segmentation – leads to specialization

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Symmetry

  Radial symmetry – animal is organized circularly Bilateral symmetry – animal has right and left halves • Accompanied by cephalization – localization of brain and specialized sensory organs at the anterior end of animal

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Coelom – body cavity

  Acoelomate – no body cavity • Packed solid with mesoderm Pseudocoelomates – body cavity incompletely lined with mesoderm

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Coelomate – body cavity completely lined with mesoderm

• • Mesentery supports internal organs.

Body movements are freer because outer wall can move independently of organs.

• Organs have more space to become complex.

• In animals without a skeleton, the coelom acts as a hydrostatic skeleton.

19.2 Introducing the invertebrates

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Sponges: Multicellularity    Saclike bodies with many pores Aquatic, largely marine Multicellular but lack organized tissues • Cellular level of organization   Interior of sponge lined with flagellated collar cells or choanocytes Filter feeder – filters food out of water using pores and collar cell microvilli  Reproduce sexually or asexually • Asexual fragmentation or budding

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Cnidarians: True Tissues

 Rich fossil record   Radially symmetrical Capture prey using ring of tentacles with cnidocytes • Cnidocyte contains nematocyst that may trap, penetrate or inject toxin   Aquatic, mostly marine 2 germ layers – ectoderm and endoderm • Tissue level of organization  2 basic body forms • Polyp – mouth directed upward from substrate • Medusa – mouth directed downward

Figure 19.9 More cnidarians

a. Portugese man-of-war is a colony of poly and medusa type individuals.

b. Coral have polyps as the dominant life stage.

c. Jellyfish have medusa as the dominant life stage.

float a. Portuguese man-of-war polyp tentacles fish b. Cup coral c. Jellyfish

a: © Runk/Schoenberger/Grant Heilman Photography; b: © Ron Taylor/Bruce Coleman; c: © Under Watercolours

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Flatworms: Bilateral Symmetry

 Have 3 germ layers   Acoelomate Planarians are free-living flatworms.

• Several body systems including a nervous system • • Cephalization – brain, eyespots and chemosensitive organs on head Incomplete digestive system – only 1 opening  Muscular pharynx • Hermaphrodites   Both male and female sex organs Cross-fertilize

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Flatworms (cont.)

 Parasitic flatworms • Tapeworms   Endoparasites Vary in size up to 20 meters  Scolex used to attach to host • Flukes     Endoparasites Oral sucker and another sucker Named for organ they inhabit Nearly 800,000 people die from blood fluke (

Schistosoma

) infections.

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Roundworms: Pseudocoelomates

2 features not yet seen to this point • Body cavity – pseudocoelom Incompletely lined with mesoderm   2.

• Complete digestive tract Both mouth and anus   Nonsegmented Occur almost everywhere – sea, fresh water, soil Free-living or parasitic

Ascaris

(intestinal), Trichinosis (skeletal muscle), Elaphantiasis (lymphatic vessels), pinworms, hookworms

19.3 Protostomes and Deuterostomes Compared

• • • •

Protostomes  Flatworms, roundworms, molluscs, annelids, arthropods Deuterostomes  Echinoderms and chordates Distinguished based on embryological development  Cell division pattern is different First embryonic opening is called blastopore.

 In protostomes becomes mouth  In deuterostomes becomes anus

19.4 Molluscs, Annelids, and Arthropods

• •

All are protostomes with a coelom.

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Molluscs

All molluscs have a body with at least 3 parts.

Visceral mass – internal organs Foot – muscular portion used for locomotion Mantle – envelopes but does not enclose visceral mass  May secrete shell Radula – tongue like with many teeth

•

3 classes of molluscs: Gastropods, Cephalopods, Bivalves

• • • Gastropods Nudibranchs, conchs, and snails Herbivores or carnivores Terrestrial snails use mantle as lung.

Cephalopods • Octopuses, squids, and nautiluses • Foot evolved into tentacles around head • • Well-developed nervous system Complex sensory organs

• • • Bivalves Clams, oysters, scallops, and mussels 2 parts to the shell Filter feeders

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Annelids  Segmented – can be seen externally in rings encircling body  Septa divide fluid-filled coelom.

• Used as hydrostatic skeleton  Complete digestive tract with specialized parts • Pharynx, esophagus, crop, gizzard, intestine   Extensive closed circulatory system Nervous system has brain and ventral nerve cord.

• Ganglia in each segment  Nephridia in excretory system • Nephridium collects waste and excretes it through pore in body wall.

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Annelids  Polychaetes • Have many setae per segment • •

Nereis

is a predator.

Other are sedentary filter feeders.

setae Figure 19.17 Other annelids

a. Clam worm spiraled tentacles b. Christmas tree worm

 Oligochaeates • Few setae per segment • • Earthworms Scavengers in dirt a: © Heather Angel; b: © James Carmichael/Nature Photographics

Figure 19.17 continued

anterior sucker posterior sucker

 Leeches • • • • No setae

c. Medicinal leech

Most freshwater but some marine or terrestrial Some free-living but most are fluid feeders Hirudin is a powerful anticoagulant.

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Arthropods

• Extremely diverse – over 1 million species As many as 30 million may exist  Success due to 6 characteristics 1.

Jointed appendages – modifications Exoskeleton – made of chitin, must be molted Segmentation – repeating body units 4.

Well-developed nervous system 5.

Variety of respiratory organs Reduced competition through metamorphosis  Larvae and adult may have different lifestyle.

Figure 19.20 Crustacean diversity

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a: © Kim Taylor/Bruce Coleman; b: © James Carmichael/Nature Photographics; c: © Natural History Photographic Agency; d: © Kjell Sandved/Butterfly Alphabet Arthropods  Crustaceans – barnacles, shrimp, lobsters, crabs, crayfish, pillbugs • • • Head and thorax fused into cephalothorax Pair of compound eyes Gills above walking legs

• Figure 19.21 More arthropods

Arthropods

Arachnids • Spiders, scorpions, ticks, mites, and harvestmen (“daddy long legs”) • Spiders  Narrow waist separates cephalothorax from abdomen.

 Inject venom and digest food externally before sucking it up  Book lungs • Scorpions  Oldest terrestrial arthropods  Nocturnal

a: © C. Allan Morgan/Peter Arnold; b: © John Bell/Bruce Coleman

Figure 19.21 continued

c • d.

Arthropods •  c(ventral): © Daniel Lyons/Bruce Coleman; c(dorsal): © Ken Lucas/Ardea; d: © David M. Dennis/Animals Animals; e: © Geof de Feu/Imagestate Mites and ticks are parasites.

Chiggers are larvae of certain mites.

• Horseshoe crabs  First pair of appendages pincerlike • •  Great interest to medical sciences Centipedes – 1 pair of appendages per segment  Carnivorous Millipedes – 2 pairs of appendages per segment  Herbivorous

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Arthropods

 • • • • Insects • • • Very numerous and diverse Entomology – study of insects Adapted to active life on land  Some have secondarily invaded aquatic habitats Body – head, thorax, abdomen Mouthparts adapted to particular way of life 3 pairs of legs 1 or 2 pairs of wings (or none)

• •

19.5 Echinoderms and Chordates

Both deuterostomes Echinoderms  Larva is free-swimming filter feeder with bilateral symmetry.

 Adults are radially symmetric without a head, brain or segmentation.

• Nerve ring around mouth extends outward  Locomotion depends on water vascular system.

• • Water enters through sieve plate Pumped into tube feet – like suction cups  No complex respiratory, excretory, or circulatory system • Fluids in coelomic cavity and water vascular system do this

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

Chordates

At some time in their life history, a chordate has 4 characteristics.

Dorsal supporting rod called notochord  Vertebrates have an endoskeleton of cartilage or bone.

Dorsal tubular nerve cord Pharyngeal pouches Postanal tail

• Figure 19.25 Invertebrate

Invertebrate chordates

chordates

 Notochord never replaced by vertebral column  Tunicates • “Sea squirts” can squirt water from siphon when disturbed.

• Larva is bilaterally symmetrical and has 4 chordate characteristics.

• Metamorphosis produces sessile adult which retains only gill slits of 4 characters.

Figure 19.25 continued • b.

Invertebrate chordates

 Lancelets • Marine chordates a few cm long • • • • Found in shallow water buried in sand Filter feeder Retain 4 chordate characteristics as adults Segmentation is present – muscle and nerve cord

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Evolutionary trends among the chordates

 Presence of vertebrae   Jaws Lungs   Jointed appendages Amniotic egg

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Fishes: First jaws and lungs

First vertebrates were jawless fishes.

3 living classes of fishes 1.

Jawless Cartilaginous Bony  • 2 latter groups have jaws Believed to have evolved from first pair of gill arches

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Jawless fishes

Figure 19.28 Diversity of fishes

 Cylindrical and up to a meter long  Smooth, scaleless skin   No jaws or paired fins Hagfish are scavengers.

toothed oral disk gill slits (seven pairs)

 Some lampreys are parasites.

a. Lamprey , a jawless fish

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 

Cartilaginous fish

Sharks, skates and rays Skeletons of cartilage not bone  3 well-developed senses enable sharks and rays to detect prey.

Sense electric currents in water Lateral line system Keen sense of smell

Figure 19.28 continued

dorsal fin gill slits (five pairs) pectoral fin jaw with b. Bull shark, a cartilaginous fish teeth

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Bony fish  Most numerous and diverse of all vertebrates  Ray-finned fishes supported by bony spikes – fins

Figure 19.28 continued

caudal fin anal fin second dorsal finfirst dorsal fin gill slit (one pair) operculum

• Perch, trout, salmon,

(covering for gills)

haddock, etc.

• Filter feeders, opportunists, or predators

pectoral fin pelvic fin

• Swim bladder serves as buoyancy organ.

 Can change density of gases to go up or down in water

c. Soldierfish, a bony fish

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Lobe-finned fishes

• Most had a lung for respiration • Evolved into amphibians • A shift in the position of the bones in the forelimbs and hind limbs lifts and supports the body.

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Amphibians: Jointed Vertebrate Limbs

  Frogs, toads, newts, and salamanders Features not seen in bony fish… • • • • • Jointed limbs Eyelids Ears Voice-producing larynx Larger brain

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Adults usually have small lungs.

• Air enters through mouth and is forced into lungs.

• Supplemental gas exchange through moist skin 

3 chambered heart

• • Mixed blood sent to all parts of body Blood sent to skin – further oxygenated 

Larval stage lives in water; adults live on land.

• Adult usually returns to water to reproduce.

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     Reptiles: Amniotic Egg  Diversified and were most abundant between 245 and 66 MYA • • Including ancestor to today’s mammals Bipedal stance of some reptiles preadaptive for evolution of wings in birds Turtles, crocodiles, snakes, and lizards Body covered in scales Use tongue as sense organ Well-developed lungs 4 chambered heart – division incomplete in some species

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Most outstanding adaptation is amniotic egg

  Eliminated need for swimming larval stage  Provides developing embryo with oxygen, food, water, removes nitrogenous waste, and protects embryo • Uses extraembryonic membranes Ectothermic – body temperature matches outside environment • Fishes, amphibians, and reptiles • Must move to warmer or cooler area to regulate temperature

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Birds   Share common ancestor with crocodiles Traits show they are reptiles • • Tail with vertebrae, clawed feet, scales Feathers are modified reptilian scales    Exact history still in dispute Endotherms – generate internal heat Nearly every anatomical feature related to flight • • • • • • • Forelimbs modified into wings Hollow, light bones laced with air cavities Horny beak instead of heavy jaws Slender neck and compact torso Efficient respiration using air sacs Completely separated 4-chambered heart Acute vision and well-developed brains

• Traditional classification based in beak and foot type

Figure 19.33 Bird’s beaks

A cardinal’s beak allows it to crack tough seeds.

A flamingo’s beak strains food from the water with bristles that fringe the mandibles.

A bald eagle’s beak a: © Kirtley Perkins/Visuals Unlimited; b: © Thomas Kitchin/Tom Stack & Associates; c: © Brian Parker/Tom Stack & Associates allows it to tear prey apart.

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Mammals: Hair and Mammary Glands

 2 chief characteristics of mammals • • Hair – provides insulation against heat loss Mammary glands – enable female to feed young without leaving them to find food

Figure 19.34 continued

• b.

Mammals

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b: © Leonard Lee Rue/Photo Researchers; c: © Fritz Prenzel/Animals Animals Marsupials • • Born in immature condition Newborns complete development inside female’s pouch.

• • Virginia opossum only marsupial north of Mexico Most Australian – koalas, kangaroos, Tasmanian wolf

 Placental mammals • • Vast majority of living mammals Extraembryonic membranes of amniote egg modified for internal development within uterus of female • Adapted to active life on land  Well developed brain – expansion of cerebral hemispheres  4 chambered heart

19.6 Human Evolution

• • • • • •

All primates share a common ancestor.

Prosimians – lemurs, tarsiers, and lorises Anthropoids – monkeys, apes, and humans Primates adapted to arboreal life  Mobile limbs  Opposable thumbs and big toes Trend toward larger and more complex brain Evolutionary tree indicates humans most closely related to African apes.

 Humans did not evolve from apes.

 Believed to share a common ancestor about 7 MYA

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Evolution of Hominins

 To be a hominin must have anatomy suitable for standing erect and walking on 2 feet – bipedal • Hominid is a family designation for humans and African apes.

 Early hominins • •

Sahelanthropus tchadensis

 – dated to 7 MYA Braincase apelike, suggestions of bipedalism

Ardipithecus ramidus

   Only skull fragments Possibly bipedal – 4.5 MYA Teeth intermediate between earlier apes and later hominids

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Australopithecines

 Possibly direct ancestor of humans  In Africa about 4 MYA 

Australopithecus afarensis

– “Lucy” • Brain small (apelike) but she stood upright and walked bipedally (humanlike) • Trail of footprints • Mosaic evolution – not all body parts change at the same rate

Figure 19.38 Australopithecus

afarensis

•

Homo habilis

 Dated between 2.0 and 1.9 MYA     May be ancestral to modern humans 45% larger brain than

A. afarensis

Cheek teeth smaller – likely omnivorous Stone tools   Enlarged portion of brain dealing with speech Beginnings of culture – encompasses human behavior and products and is dependent upon capacity to speak and transmit knowledge

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Homo erectus

      Found in Africa, Asia, and Europe Dated between 1.9 and 0.3 MYA Similar in appearance but may be several species Larger brain and flatter face compared to

H. habilis

Much taller Robust and muscled skeleton still like australopithecines  Believed to have appeared in Africa and migrated into Asia and Europe   First to use fire Fashioned more advanced tools

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Evolution of modern humans

 Most researchers believe

Homo sapiens

evolved from

Homo erectus

but details differ  Multiregional continuity hypothesis • • Evolved separately in Asia, Africa, and Europe from

Homo erectus

Homo sapiens

Opponents argue this is highly unlikely to evolve so similarly in 3 widespread areas.

 Replacement model or out-of-Africa hypothesis •

Homo erectus

evolved to

Homo sapiens

only in Africa and then migrated outward.

• Suggests we are more genetically similar • Supported by research on human mitochondrial DNA

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       Neanderthals

Homo neandertalensis

  Take name from German valley Possibly already present when Cro-Magnons showed up Competition may have made Neanderthals go extinct Neanderthals had massive brow ridges.

Nose, jaws, and teeth protruded far forward.

Forehead low and sloping No chin Heavily muscled Sturdy build may have helped conserve body heat in last Ice Age  Culturally advanced • • • Most lived in caves but may have built homes Variety of stone tools Buried dead with flowers and tools – religion?

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Cro-Magnons

Homo sapiens

 Thoroughly modern appearance   Advanced tools May have been first to make knifelike blades and throw spears • May be responsible for extinction of many larger mammals like giant sloth, mammoth, saber toothed tiger and giant ox  Hunted cooperatively   Perhaps first to have language Culture included art