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Chapter 19Evolution of
Animals
Key Innovations Distinguish Invertebrate Groups
19-2
19.1 Animals have distinctive characteristics
Animals are multicellular eukaryotes Chemoheterotrophs that acquire nutrients from an
external source and digest it internally Usually carry on sexual reproduction and begin life only
as a fertilized diploid egg Developmental stages to produce specialized tissues
within organs with specific functions Muscles and nerves characterize animals
Allow animals to perform flexible movements
19-3
Figure 19.1 Developmental stages of a frog
19-4
19.2 Animals most likely have a protistan ancestor
Two hypotheses on origin of animals Multinucleate Hypothesis Animals arose from a ciliated protist in stages
The ciliate would have acquired multiple nuclei, and then it would have become multicellular
Colonial Flagellate Hypothesis Animals descended from an ancestor that resembled a
spherical colony of flagellated cells
19-5
Figure 19.2 The colonial flagellate hypothesis
19-6
Radial and Bilateral Symmetry
19-7
19.3 The traditional evolutionary tree of animals is based on seven key innovations (figure 19.3A)
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Animal Body Cavities
Figure 19.3B Types of body cavity
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APPLYING THE CONCEPTS—HOW SCIENCE PROGRESSES
19.4 Molecular data suggest a new evolutionary tree for animals
In traditional tree, protostomes are restricted to three phyla, which have a coelom Arthropods, Annelids, and Molluscs
Evolutionary tree based on molecular data suggests many more animal phyla should be designated protostomes because their rRNA sequences are so similar Segmentation doesn’t play a defining role in the
evolutionary tree based on molecular data
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Figure 19.4A Proposed new evolutionary tree
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Figure 19.4B Roundworms and arthropods are molting animals
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19.5 Some animal groups are invertebrates and some are vertebrates
For convenience, the animal phyla have been divided into Invertebrates - those that do not have an
endoskeleton of cartilage and bone Vertebrates - those that do have an endoskeleton
Animals evolved in the sea and most animals still live in the water Among the invertebrates only the molluscs, annelids,
and arthropods have terrestrial representatives19-13
19-14
19.6 Sponges are multicellular invertebrates
Only animal without true tissue, organized at cellular level Body of Sponges - phylum Porifera because their bodies
are perforated by pores Filter feeder, also called a suspension feeder, because it filters
suspended particles from water Endoskeleton
Have fibers of spongin, a modified form of collagen Typically have an endoskeleton also with spicules, small, needle-
shaped structures with one to six rays Reproduction
Reproduce asexually by budding Reproduce sexually as egg and sperm are released into central
cavity Zygote develops into a flagellated larva that may swim to a new location
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Figure 19.6 Sponge anatomy
19-16
19.7 Cnidarians have true tissues
Cnidarians (phylum Cnidaria) - an ancient group of invertebrates Most in the sea, but a few freshwater species
Radially symmetrical and capture their prey with a ring of tentacles that have specialized stinging cells, cnidocytes Each cnidocyte has a capsule called a nematocyst,
containing a long, spirally coiled, hollow thread Two basic body forms
Polyp - mouth is directed upward from the substrate Medusa - mouth is directed downward
Cnidarians - a sac body plan with only one opening
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Figure 19.7A Cnidarian diversity
19-18
Figure 19.7B Anatomy of Hydra, a polyp
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19.8 Free-living flatworms have bilateral symmetry
Flatworms (phylum Platyhelminthes) First phylum with bilateral symmetry
Have three germ layers Ectoderm from which body wall develops Endoderm from which digestive cavity develops Mesoderm which contributes to organ formation
Have no coelum and are called acoelomates Planarians have several body systems
Digestive System - pharynx leads to gastrovascular cavity Excretory System - a series of interconnecting canals Reproductive System - Hermaphrodites (both male and female
sex organs) and perform cross-fertilization Nervous System - brain and two lateral nerve cords are joined
by cross-branches called transverse nerves 19-20
Figure 19.8 Planarian anatomy
19-21
19.9 Some flatworms are parasitic
Tapeworms Endoparasites (internal parasites) of various vertebrates,
including humans Vary in length from a few millimeters to 20 meters
Tough body covering resistant to the host’s digestive juices Scolex bears hooks and suckers for attachment to the intestinal
wall of the host Flukes
Endoparasites of various vertebrates Anterior end of the animal has an oral sucker and at least one
other sucker used for attachment to the host Nearly 800,000 persons die each year from an infection called
schistosomiasis
19-22
Figure 19.9A Tapeworm (Taenia solium) anatomy and life cycle
19-23
Figure 19.9B Sexual portion of blood fluke (Schistosoma spp.) life cycle
19-24
19.10 Roundworms have a pseudocoelom and a
complete digestive tract Roundworms (phylum Nematoda) possess two anatomic
features not previously seen body cavity - pseudocoelom and is incompletely lined with
mesoderm complete digestive tract - it has both a mouth and an anus
Nonsegmented, meaning that they have a smooth outside body wall
Ascaris Humans are infected with a roundworm called Ascaris when eggs
enter the body via uncooked vegetables Other Roundworm Parasites
Trichinosis - serious human infection acquired when humans eat meat that contains encysted larvae
Elephantiasis is caused by a roundworm called a filarial worm, which utilizes mosquitoes as a secondary host
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Figure 19.10A Ascaris Figure 19.10b Encysted Trichinella larva
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Figure 19.10C Elephantiasis
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19.11 A coelom gives complex animal groups certain advantages
Coelom - body cavity completely lined by mesoderm Two groups
Protostomes - Molluscs, annelids, and arthropods Deuterostomes - echinoderms and chordates
Two major events can be used to distinguish protostomes from deuterostomes Blastopore - protostomes: mouth appears near blastopore;
deuterostomes: anus appears near blastopore Coelom formation - protostomes: splitting produces the coelom;
deuterostomes: the coelom arises as a pair of mesodermal pouches from the gut wall
Advantages of a Coelom Body movements are freer because outer wall can move
independently of the enclosed organs Ample space of a coelom allows complex organs and organ systems
to develop19-28
Figure 19.11 Protostomes compared to deuterostomes
19-29
19.12 Molluscs have a three-part body plan
All molluscs (phylum Mollusca) have a body composed of at least three distinct parts The foot - strong, muscular portion used for locomotion Visceral Mass - soft-bodied portion that contains internal organs The mantle - covering that envelops the visceral mass
The mantle may secrete an exoskeleton called a shell Gastropods (meaning stomach-footed) including snails and
nudibranchs Animal moves by muscle contractions that pass along its ventrally
flattened foot Cephalopods (meaning head-footed) including octopuses, squids,
and nautiluses The foot has evolved into tentacles about the head
Bivalves (shells have two part) including clams, oysters, scallops, and mussels The clam is a filter feeder and food particles and water enter the mantle
cavity by way of a siphon19-30
Figure 19.12A Body plan of a typical mollusc
19-31
Figure 19.12B Three groups of molluscs
19-32
19.13 Annelids are the segmented worms
Annelids (phylum Annelida) are segmented, as can be seen externally by the rings that encircle the body Partitions called septa divide the well-developed, fluid-filled
coelom, which is used as a hydrostatic skeleton Excretory system consists of nephridia, tubules that collect
waste material and excrete it through an opening in the body wall Oligochaetes
Earthworm is an oligochaete because it has few setae, bristles that anchor the worm
Polychaetes Most annelids are polychaetes (having many setae per segment)
that live in marine environments Leeches
Have no setae, but have the same body plan as other annelids Blood suckers that are able to keep blood flowing and prevent
clotting19-33
Figure 19.13A Earthworm anatomy
19-34
Figure 19.13B Other annelids
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19.14 Arthropods have jointed appendages
Arthropods (phylum Arthropoda) are extremely diverse More than one million species have been discovered
Six characteristics Jointed appendages Exoskeleton Segmentation Well-developed nervous system Variety of respiratory organs Reduced competition through metamorphosis
19-36
Figure 19.14A Exoskeleton and jointed appendages of a crayfish, an arthropod
19-37
Figure 19.14B Monarch butterfly metamorphosis
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19.15 Well-known arthropods other than insects
Crustaceans - name derived from their hard, crusty exoskeleton Largely marine arthropods that include crabs, barnacles,
shrimps, and crayfish Head usually bears a pair of compound eyes and five
pairs of appendages
Arachnids include spiders, scorpions, ticks, mites, and harvestmen Spiders have a narrow waist that separates the
cephalothorax, with four pairs of legs, from the abdomen19-39
Figure 19.15A Crustacean diversity
19-40
Figure 19.15B Centipede and millipede
19-41
Figure 19.15C Spider and relatives
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19.16 Insects, the largest group of arthropods, are adapted
to living on land
Insects - so numerous (>one million species) and diverse that the study of this one group is a major specialty in biology called entomology
Adapted to a life on land Body is divided into head, thorax, and abdomen Mouthparts adapted to each species’ way of life Wings enhance an insect’s ability to survive
way of escaping enemies, finding food, facilitating mating, and dispersing offspring
19-43
Figure 19.16 Insect diversity
19-44
19.17 Echinoderms are radially symmetrical as adults
Echinoderms (phylum Echinodermata) lack chordate features, but are related to because they are deuterostomes Radially, not bilaterally, symmetrical as adults
Their larva is a bilaterally symmetrical filter feeder Adult echinoderms do not have a head, brain, or segmentation
Their nervous system consists of nerves in a ring around the mouth extending outward radially
Locomotion by a water vascular system that pumps water into many tube feet, expanding them
No complex respiratory, excretory, or circulatory system Fluids within the coelomic cavity and the water vascular system
carry out many of these functions In ecosystems, most feed on organic matter in the sea or
substratum Sea stars prey upon crustaceans, molluscs, and other invertebrates
19-45
Figure 19.17 Echinoderm structure and diversity
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Further Innovations Allowed Vertebrates to Invadethe Land Environment
19-47
19.18 Four features characterize chordates
Dorsal supporting rod (notochord) extends the length of the body
Dorsal tubular nerve cord contains a canal filled with fluid
Pharyngeal pouches only during embryonic development in most vertebrates
A postanal tail extends beyond the anus
19-48
Figure 19.18 The four chordate characteristics
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19.19 Invertebrate chordates have a notochord as adults
A few of the invertebrate chordates never replace the notochord with the vertebrae Tunicates (subphylum Urochordata) live on the
ocean floor as filter feeders Larva is bilaterally symmetrical and has the four chordate
characteristics Metamorphosis produces the sessile adult
Lancelets (subphylum Cephalochordata) marine chordates only a few centimeters long Lancelets retain the four chordate characteristics as adults
19-50
Figure 19.19 The invertebrate chordates
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19.20 The evolutionary tree of vertebrates is based on
five key features
Vertebrates Fishes, amphibians, reptiles, birds, and mammals Vertebrae are most obvious feature Vertebral column is flexible because vertebrae are
separated by disks, which cushion the vertebrae The soft center of a disk presses on the spinal cord
Derived Characters Among Vertebrates Jaws, Lungs, Jointed Limbs, and Amniotic Eggs
19-52
Figure 19.20 Evolutionary tree of the chordates
19-53
19.21 Jaws and lungs evolved among the fishes
Jawless Fishes (Class Agnatha) Cylindrical and up to a meter long Smooth, scaleless skin, no jaws or paired fins
Cartilaginous Fishes (Class Chondrichthyes) includes sharks, the rays, and the skates Skeletons of cartilage, instead of bone Shark senses
Able to sense electric currents in water Lateral line system senses pressure waves caused by fish Keen sense of smell
Bony Fishes (Class Osteichthyes) most numerous and diverse of all vertebrates Ray-finned fishes - use their fins to balance and propel body
Have a swim bladder, which usually serves as a buoyancy organ Bony scales that protect body but do not prevent water loss
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Figure 19.21A Evolution of jaws
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Figure 19.21B Diversity of fishes
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Figure 19.21C This transitional form links the lobes of the lobe-finned fishes to the limbs of ancestral amphibians
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19.22 Amphibians are tetrapods that can move on land
Amphibians (class Amphibia) means living on both land and in the water, represented by frogs, toads, newts, and salamanders
Characteristics Adults have small lungs - air enters the mouth by way
of nostrils Respiration is supplemented by gas exchange
through the smooth, moist, skin
Most members lead an amphibious life Larval stage lives in water, and adult stage is on land
19-58
Figure 19.22 Frogs and salamanders are well-known amphibians
19-59
19.23 Reptiles have an amniotic egg and can reproduce on land
Reptiles (class Reptilia) diversified and most abundant between 245 and 66 MYA
The reptiles living today are mainly alligators, crocodiles, turtles, snakes, lizards, and tuataras
Body is covered with hard, keratinized scales, which protect animal from desiccation and from predators
Fertilization is internal, and the female lays leathery, flexible, shelled eggs Amniotic egg made development on land possible and
eliminated the need for a swimming larval stage Fishes, amphibians, and reptiles are ectotherms
Body temperature matches the temperature of their environment
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Amniotic Egg
19-61
Figure 19.23 Reptilian diversity
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19.24 Birds have feathers and are endotherms
Birds (class Aves) are characterized by the presence of feathers Lay a hard-shelled amniotic egg
Data suggests birds are related to bipedal dinosaurs and should be classified as such
Birds are adapted to fly Forelimbs are modified as wings Hollow, light bones Horny beak has replaced jaws with teeth
Birds are endotherms and generate internal heat May be associated with efficient nervous, respiratory, and
circulatory systems Seasonal migration of many species over very long distances
Navigate by day and night, whether it’s sunny or cloudy, by using the sun and stars and even the Earth’s magnetic field to guide them
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Figure 19.24A Bird flight
19-64
Figure 19.24B Types of bird beaks
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19.25 Mammals have hair and mammary glands
Mammals (class Mammalia) evolved during Mesozoic from reptiles called therapsids
Two chief characteristics Hair: Mammals are endotherms, and hair aids
temperature control Milk-producing mammary glands: enable females to
feed (nurse) their young without leaving them to find food
19-66
Monotremes and Marsupials
Monotremes - mammals that have a cloaca, a terminal region of the digestive tract serving as a common chamber for feces, excretory wastes, and sex cells Also lay hard-shelled amniotic eggs
Marsupials - begin their development inside the female’s body, but they are born in a very immature condition Newborns crawl up into a pouch on their mother’s
abdomen
19-67
Figure 19.25A Monotremes and marsupials
19-68
Placental Mammals
Placental mammals - extraembryonic membranes of the reptilian egg are modified for internal development within the uterus of the female Chorion contributes to the fetal portion of the placenta, while
a part of the uterine wall contributes to the maternal portion Nutrients, oxygen, and waste exchanged between fetal and
maternal blood Distinguished by their mode of locomotion
Bats have membranous wings supported by digits Horses have long, hoofed legs; and whales have paddlelike
forelimbs Distinguished by the way of obtaining food
Mice have continuously growing incisors Horses have large, grinding molars Dogs have long canine teeth
19-69
Figure 19.25B Placental mammals
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
19.26 Many vertebrates provide medical treatments for humans
Hundreds of pharmaceutical products come from vertebrates Animals that produce poisons and toxins give us
medicines that benefit us Some produce proteins similar to human proteins to
be used in medical treatment Powerful applications of genetic engineering
found in development of drugs and therapies for human diseases Xenotransplantation, transplantation of vertebrate
tissues and organs into human beings Use of transgenic vertebrates for medical purposes
does raise health and ethical concerns 19-71
Figure 19.26 Vertebrates used for medical purposes
19-72
Connecting the Concepts:Chapter 19
As terrestrial mammals, humans might assume that terrestrial species are more successful than aquatic ones If not for the myriad types of terrestrial insects, there would be
more aquatic species than terrestrial ones on Earth Adaptative radiation of mammals has taken place on
land, and this might seem impressive to some Actually, the number of mammalian species (4,800) is small
compared to the molluscs (110,000 species) Size and complexity of the brain is also sometimes cited
as a criterion by which vertebrates are more successful than other living things This characteristic has been linked to others that make an
animal prone to extinction Long life span, slow to mature, have few offspring, expend much
energy caring for their offspring, and tend to become extinct if their normal way of life is destroyed
19-73