This document provides an outline and overview of the invertebrates chapter of a biology textbook. It discusses the key characteristics of animals and introduces the major animal classifications including Parazoa, Radiata, Lophotrochozoa, Ecdysozoa, and Deuterostomia. Examples of phyla from each group are described, focusing on their defining anatomical features and life cycles.

1. 1
Chapter 25
Lecture Outline
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2. 2
Chapter 25
The Invertebrates
Chapter Outline:
 Characteristics of Animals
 Animal Classification
 Parazoa: Sponges, the First Multicellular Animals
 Radiata: Jellyfish and Other Radially Symmetric Animals
 Lophotrochozoa: The Flatworms, Rotifers, Bryozoans,
Brachiopods, Mollusks, and Annelids
 Ecdysozoa: The Nematodes and Arthropods
 Deuterostomia: The Echinoderms and Chordates

3. Characteristics of Animals
 Multicellular heterotrophs
 Cells lack cell walls
 Cells exist in extensive extracellular matrix
 Unique cell junctions
 Most have nerves, muscles, and capacity to move
 Able to reproduce sexually
 Specialized sensory structures and nervous system
 Hox genes pattern the body axis 3

4.  Most biologists agree kingdom is monophyletic
 About 35 recognized animal phyla
 Most likely ancestor was a colonial flagellated
protist similar to choanoflagellates
 Some are colonial
 Some cells my have taken on specialized functions
4
Animal Classification

5. 5
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Metazoa
Parazoa Eumetazoa
Radiata Bilateria
Protostomia Deuterostomia
Lophotrochozoa Ecdysozoa
Chordata
Echinodermata
Arthropoda
Nematoda
Annelida
Mollusca
Brachiopoda
Rotifera
Platyhelminthes
Cnidaria and Ctenophora
Porifera
Parazoa
Radiata
Critical innovations
KEY
Most with lophophore
or trochophore larva
Tissues
Multicellularity
Protostome development
Ecdysis
Bilateral symmetry
Common ancestor of animals
and choanoflagellates
Deuterostome
development,
endoskeleton
Kingdom Animalia
Bryozoa

6. BIOLOGY PRINCIPLE
All species (past and present)
are related by an evolutionary history
All animals are believed to be derived
from a choanoflagellate-like ancestor
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7. Origin of animals
 The closest living relative of animals is
believed to be a flagellated protist known as
a choanoflagellate
 Tiny, single-celled or colonial organisms, with a
single flagellum surrounded by a collar of
cytoplasmic tentacles
 Colonial choanoflagellate cells are very
similar to choanocyte cells of sponges
7

8. 8
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Sponge cell
(choanocyte)
Choanoflagellate cell
(a) Colonial choanoflagellate (b) Sponge

9. Traditional classification based on
body plans
 Morphological and developmental features
traditionally used to classify animals:
1. Presence or absence of different tissue types
2. Type of body symmetry
3. Specific features of embryonic development
9

10. 1. Tissues
 Metazoa – all animals
 Metazoa divided based on whether there are
specialized tissues
 Parazoa (without specialized tissues or organs)
 Porifera – sponges
 Eumetazoa (more than one type of tissue and organ)
10

11. 2. Symmetry
 Eumetazoa are radially symmetrical or bilaterally
symmetrical
 Bilateria (bilateral animals)
 Have cephalization and dorsal and ventral sides
 3 germ layers
 Radiata (radial animals)
 Have oral and aboral sides
 2 germ layers
11

12. 12
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(c) Eumetazoa: three tissue types
Bilateria: bilateral symmetry
(b) Eumetazoa: two tissue types
Radiata: radial symmetry
(a) Parazoa: no tissue types
a: © E. Teister/agefotostock; b: © Gavin Parsons/ Getty Images; c: © Tui de Roy/Minden Pictures

13.  Number of cell layers
 Bilateria are triploblastic – 3 layers
 Radiata are diploblastic – 2 layers
 Cell layers develop during gastrulation
 Inner layer – endoderm
 Outer layer – ectoderm
 Mesoderm - 3rd layer in bilateral animals
 Forms muscles and most other organs
13

14. 14

15. 3. Embryonic development
 Protostome
 Spiral cleavage
 Cleavage is determinate
 Blastopore becomes mouth
 Deuterostome
 Radial cleavage
 Cleavage is indeterminate – pluripotent stem cells
 Blastopore becomes anus
15

16. 16
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Deuterostomes Protostomes
Blastopore
becomes mouth.
Blastopore
becomes anus.
Radial cleavage
Cell
excised
4-cell
embryo
Development arrested
Cell
excised
4-cell
embryo
Normal embryo Normal embryo
(a) Fate of blastopore (b) Fate of embryonic cells (c) Cleavage pattern
Top view
Indeterminate cleavage
Top view
Spiral cleavage
Side view
Determinate cleavage
Side view

17. Coelom
 In the past, the presence or
absence of a coelom was
used to construct animal
phylogeny
 This feature is now thought
to be unreliable because
 Coeloms may have been
lost over evolutionary time
 And, the coelom may have
arisen more than once
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Muscle layer
(from mesoderm)
17
Body covering
(from ectoderm)
Coelom
(fluid-filled
space)
Earthworm
(a) Coelomate
Tissue layer
suspending organs
(from mesoderm)
Digestive tract
(from endoderm)
Muscle layer
(from mesoderm)
Body covering
(from ectoderm)
Pseudocoelom
(fluid-filled
space)
Nematode
Digestive tract (from endoderm)
Muscle layer
(from mesoderm)
Body covering
(from ectoderm)
(b) Pseudocoelomate
Flatworm
(c) Acoelomate
Digestive tract
(from endoderm)
Mesenchyme
(from mesoderm)

18. Other methods of classification
 Possession of exoskeleton
 Development of notochord
 Presence or absence of segmentation
18

19. 19

20.  Phylum Porifera – Sponges
 Loosely organized and lack tissues
 Multicellular with several types of cells
 8,000 species, mostly marine
 No apparent symmetry
 Adults sessile, larvae free-swimming
20
Parazoa: Sponges, the First
Multicellular Animals

21. 21
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Parazoa
Cnidaria and
Ctenophora
Lophotrochozoa
Radiata Bilateria
Porifera
Common ancestor of
animals and choanoflagellates
Deuterostomia
Ecdysozoa
Protostomia
Eumetazoa
Parazoa

22.  Water drawn through pores into central cavity
 Flows out through osculum (opening at top)
 Choanocytes line cavity
 Trap and eat small particles and plankton
 Amoebocytes absorb food from choanocytes,
digest it, and carry to other cells
 Sponges unique in using intracellular digestion
 Some have sharp spicules or tough spongin
22

23.  Sponges reproduce
 Sexually
 Most hermaphrodites producing eggs and sperm
 Gametes are derived from amoebocytes or choanocytes
 Asexually
 Small fragment or bud may detach and form a new sponge
23

24. 24

25.  Phylum Cnidaria
 Phylum Ctenophora
 Radial symmetry
 Mostly marine
 Only two embryonic germ layers
 Diploblastic
 Ectoderm and endoderm
 Mesoglea connects layers
25
Radiata

26. 26
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Lophotrochozoa
Radiata Bilateria
Porifera
Parazoa
Cnidaria and Ctenophora
Deuterostomia
Ecdysozoa
Protostomia
Eumetazoa
Radiata
a

27.  First clade with true tissues
 Gastrovascular cavity for extracellular digestion
 Allows ingestion of larger food particles
 Advance over sponge’s intracellular digestion
 True nerve cells arranged in nerve net
 No central control organ
27

28. Phylum Cnidaria
 Two different body forms
 Sessile polyp – tubular body with tentacles
surrounding opening (mouth and anus)
 Motile medusa – umbrella-shaped body with a
mouth on the underside surrounded by tentacles
 Cnidocytes contain nemotocysts
 Hairlike trigger – cnidocil
 Some are sticky, others sting
 Simple muscles and nerves
 Not true muscles (not of mesoderm origin)
28

29. 29

30. BIOLOGY PRINCIPLE
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Structure determines function
The inverted, umbrella-shaped
medusae are free-swimming.
30
Whereas the tubular,
polyp forms are sedentary.

31. 31

32. 32

33. Phylum Ctenophora
 Comb jellies
 Less than 100 species – all marine and look like jellyfish
 First complete gut – mouth and anus
 Eight rows of cilia on surface beat for propulsion
 Largest animals to use cilia for locomotion
 Two long tentacles without stinging cells
 Colloblasts secrete sticky substance
 Hermaphroditic
 Bioluminescent 33

34. 34

35.  Members have either a lophophore (a crown of
ciliated tentacles)
 Bryozoans
 Brachiopods
 Rotifers
 Or have a trochophore larval stage
 Mollusks
 Annelids
 Platyhelminthes (flatworms)
35
Lophotrochozoa: The Flatworms,
Rotifers, Bryozoans, Brachiopods,
Mollusks, and Annelids

36. Phylum Platyhelminthes
 Flatworms
 Lack a specialized respiratory
or circulatory system
 Respire by diffusion
 Among first animals with active
predatory lifestyle
 Bilaterally symmetrical with a head
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36
Lophotrochozoa
Platyhelminthes
Rotifera
Bryozoa
Brachiopoda
Lophotrochozoa
Annelida
Protostomia
Bilateria
Cnidaria and Ctenophora
Radiata
Porifea
Parazoa Eumetazoa
Ecdysozoa
Deuterostomia
Mollusca

37. Ocelli (eyespots)
Auricles
Cerebral ganglia
Lateral nerve
cords
Protonephridia
 First triploblast – three embryonic germ layers
 Mesoderm key innovation – allowed sophisticated organs
 Acoelomate – lacking fluid-filled cavity
37
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Gastrovascular
cavity
Transverse
nerve
Mouth Pharynx
Pharyngeal
chamber

38.  An incomplete digestive system
 Distinct excretory system with protonephridia
and flame cells
 Light sensitive eyespots or ocelli
 Cerebral ganglia receive input
 Retain nerve net with beginning of more
centralized nervous system
 Sexual or asexual reproduction
 Most hermaphroditic but do not self fertilize
38

39.  Turbellaria – Free-living, Planaria
 Monogenea – Fish flukes
 Trematoda – Flukes, parasitic
 More complex life cycle with multiple hosts
 Chinese liver fluke, Clonorchis sinensis
 Blood flukes, Schistosoma spp., most common
parasitic trematode infecting humans
 Cestoda – Tapeworms, parasitic
 Two separate host species in life cycle
39
Four classes of Platyhelminthes

40. 40

41. 41
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(a)
(b)
Scolex
Proglottids
a: © Wolfgang Poelzer/Wa./agefotostock; b: © Biophoto Associates/Photo Researchers, Inc.

42. BIOLOGY PRINCIPLE
Biology affects our society
About 1% of U.S. cattle are infected by beef
tapeworms. Consuming beef that is not sufficiently
well cooked can lead to infection by these
parasites.
42

43. 43

44. Phylum Rotifera
 Named for ciliated crown
or corona that looks like a
rotating wheel
 2000 species – mostly
freshwater
 Digestive tract with mouth
and anus so they can feed
continuously
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44
Lophotrochozoa
Platyhelminthes
Rotifera
Bryozoa
Brachiopoda
Lophotrochozoa
Protostomia
Bilateria
Porifea
Cnidaria and Ctenophora
Radiata
Parazoa Eumetazoa
Annelida
Ecdysozoa
Deuterostomia
Mollusca

45. 45

46.  Phylum Bryozoa
 Small colonial animals
 Look like plants
 About 4,000 species
 Animal secretes and
lives inside zoecium
 Phylum Brachiopoda
 Marine with 2 shells
 Dorsal and ventral valve
 About 300 living species
 Both have lophophore –
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Platyhelminthes
Bryozoa
Rotifera
Bryozoa
Brachiopoda
Lophotrochozoa
Mollusca
Protostomia
Annelida
Ecdysozoa
Bilateria
Porifea
Cnidaria and Ctenophora
Radiata
Parazoa Eumetazoa
Deuterostomia
ciliary feeding and respiration device 46

47. 47

48. Phylum Mollusca
 Large phylum with
over 100,000 species
 Soft body often with a shell
 Foot, visceral mass and
mantle
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 Coelom confined to small area
around heart
 Open circulatory system
 Metanephridia
 Radula – unique tongue-like
organ
48
Platyhelminthes
Lophatrochozoa
Rotifera
Bryozoa
Brachiopoda
Lophotrochozoa
Annelida
Ecdysozoa
Protostomia
Bilateria
Porifea
Cnidaria and Ctenophora
Radiata
Parazoa Eumetazoa
Deuterostomia
Mollusca

49. 49
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Visceral mass
Mantle
Anus
Foot
Nerve Intestine
Gill
cords
Gonads
Radula
Digestive gland
Shell
Mouth
Stomach
Heart Metanephridium
Mantle cavity
Coelom

50.  Most shells have three layers, laid down from
mantle secretions
 Separate sexes (some hermaphroditic)
 Mostly external fertilization
 Some internal (key to snails colonizing land)
 Trocophore larva develops into veliger with
rudimentary foot, shell and mantle
 8 classes
 Most common: polyplacophorans, gastropods,
bivalves and cephalopods
50

51. 51

52. 52

53. Phylum Annelida
 Rings are distinct
segments separated
by a septum
 Advantages of
segmentation
1. Repetition
provides backup
2. Coelom acts as
hydrostatic skeleton
3. Permits specialization
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53
Lophotrochozoa
Rotifera
Bryozoa
Brachiopoda
Annelida
Ecdysozoa
Protostomia
Bilateria
Porifea
Cnidaria and Ctenophora
Platyhelminthes
Radiata
Parazoa Eumetazoa
Deuterostomia
Mollusca
Lophotrochozoa

54.  Double transport
system
 Circulatory system
and coelomic fluid
both carry nutrients,
wastes and
respiratory gases
54

55.  Digestive system complete and unsegmented
 Sexual reproduction involves two individuals
(sometimes separate sexes, others
hermaphroditic) with internal fertilization
 Asexual reproduction by fission
 15,000 species
 All annelids except leeches have setae on each
segment
55

56. Two major groups:
 Errantia
 free-ranging predators with eyes and jaws
 long setae bristle out of body
 supported on parapodia “feet”
 often brightly colored
 Sedentaria
 tube worms, earthworms, and leeches
 setae close to body for anchoring in burrows
 reduced head appendages
56

57. 57
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(b)
a: © WaterFrame/Alamy; b: © J. W. Alker/agefotostock; c: © Colin Varndell/Getty
Images; d: © St. Bartholomew’s Hospital/Photo Researchers, Inc.;
(d)
(c)
(a)

58.  Separation from
Lophotrochozoa supported
by both molecular data and
morphology
 Ecdysis – molting
 All ecdysozoans possess
a cuticle for support and
protection
 Some have metamorphosis
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58
Ecdysozoa: The Nematodes
and Arthropods
Nematoda
Ecdysozoa
Protostomia
Bilateria
Cnidaria and Ctenophora
Radiata
Porifea
Parazoa Eumetazoa
Deuterostomia
Arthropoda
Lophotrochozoa
Ecdysozoa

59. Phylum Nematoda
 Roundworms
 In nearly all habitats from poles to tropics
 Over 20,000 species (more undiscovered)
 Tough collagen cuticle covers body
 Longitudinal but not circular muscles
 Pseudocoelom acts as hydrostatic skeleton
and circulatory system
 Complete digestive tract, mouth with stylets
59

60.  Reproduction usually sexual with separate
males and females
 Internal fertilization
 Caenorhabditis elegans – model organism
 Large number of species parasitic in humans
and other vertebrates
 Ascaris lumbricoides – over 1 billion people infected
 Necator americanus – hookworm
 Enterobius vermicularis – pinworm
 Wuchereria bancrofti – causes elaphantiasis
60

61. 61

62. Phylum Arthropoda
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62
 Perhaps most successful phylum
 ¾ of all described living species
 Success related to body plan
that permits them to live in
all major biomes
 Exoskeleton made of chitin and
protein
 Can be extremely tough or
soft and flexible
 Relatively impermeable to water
Nematoda
Ecdysozoa
Protostomia
Bilateria
Cnidaria and Ctenophora
Radiata
Porifea
Parazoa Eumetazoa
Deuterostomia
Arthropoda
Lophotrochozoa
Ecdysozoa

63.  Segmented with appendages for locomotion,
food handling, or reproduction
 Tagmata – fused body segments
 Extensive cephalization
 Well developed sensory organs for sight, touch,
smell, hearing and balance
 Compound eyes – ommatidia
 Sophisticated brain consists of cerebral ganglia
connected to several smaller ventral ganglia
63

64.  Open circulatory system
 Gas exchange – gills, tracheal system with
spiracles or book lungs
 Complex digestive system
 Excretion – metanephridia or Malpighian
tubules
64

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Head Thorax Abdomen
Antennae
Compound
eye
Spiracles
Wings

66. 66
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Ancestral
arthropod
Chelicerates
Myriapods
Hexapods
Crustaceans
Pancrustacea

67.  Subphylum Trilobita
 Extinct early arthropods, bottom feeders,
little specialization of body segments
 Subphylum Chelicerata
 Spiders, scorpions, ticks and mites
 Two tagmata – cephalothorax and abdomen
 Four pairs walking legs plus pedipalps and
chelicerae
67

68. 68

69.  Subphylum Myriapoda
 Class Diplopoda – millipedes
 2 pairs of legs per segment, herbivorous
 Class Chilopoda – centipedes
 1 pair of legs per segment, carnivorous
69
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(a) Two millipedes (b) A centipede
a: © David Aubrey/Corbis; b: © Larry Miller/Photo Researchers, Inc

70.  Subphylum Hexapoda
 More species of insects than all other animal species
combined
 Wings crucial to success – outgrowths of body wall
 35 orders – differences in wings and mouthparts
 Separate sexes with internal fertilization
 Metamorphosis
 Complete – 4 stages, adult and larval stages very different
 Incomplete – 3 stages, young resemble miniature adults
70

71. 71

72. 72

73. 73

74. 74
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Adult grasshopper
Nymph stages
(b) Incomplete metamorphosis
Fertilized
egg

75.  Subphylum Crustacea
 Crabs, lobsters, barnacles and shrimp
 Marine, fresh water and terrestrial
 Unique in having two pairs of antennae
 Mouthparts: mandibles, maxillae and maxillipeds
 Walking legs and swimmerets
 Cuticle covering head extends over cephalothorax
 Nauplius larva very different from adult
75

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Cephalothorax (13 segments) Abdomen (6 segments)
76
Eye
Carapace
Swimmerets
Walking legs
Antennule
Antenna
Mandible
Maxillae
Maxillipeds
Cheliped (first leg)
Claw

77. 77

78.  Phylum Echinodermata
 Modified radial symmetry – 5 parts
 Secondary – larvae are bilateral
 Cephalization absent
 Phylum Chordata
78
Deuterostomia:
The Echinoderms and Chordates

79. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parazoa
Echinodermata
Radiata Bilateria
Porifera
Cnidaria and Ctenophora
Ecdysozoa
Protostomia
Eumetazoa
Lophotrochozoa
Deuterostomia
Chordata
Deutrostomia

80.  No brain – simple nervous system
 Endoskeleton covered with spines and pedicellariae
 Water vascular system with tube feet functions in
movement, gas exchange and feeding
 No excretory organs – respiration and excretion by
diffusion
 Autotomy – Can intentionally detach body part that will
later regenerate
 Reproduce sexually with separate sexes and external
fertilization
80

81. 81

82. Phylum Chordata
 Key distinguishing
innovations
1. Notochord
2. Dorsal hollow nerve cord
3. Pharyngeal slits
4. Postanal tail
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82
Echinodermata
Radiata Bilateria
Porifera
Parazoa
Cnidaria and Ctenophora
Ecdysozoa
Protostomia
Eumetazoa
Lophotrochozoa
Deuterostomia
Chordata
Deutrostomia

83. Intestine
Muscular
segments
 All chordates exhibit all four characteristics at
some time during development
83
Postanal
tail
Notochord Dorsal hollow
Nerve cord
Pharyngeal
(gill) slits
Brain
Heart
Stomach
Anus
Mouth
Pharynx
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84. Subphylum Cephalochordata
 Lancelets
 26 species
 All marine filter feeders
 Have 4 hallmarks
 Gas exchange across body surface
 Usually sessile but can leave burrow and swim
84

85. 85
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Notochord
Dorsal hollow nerve cord
Tentacles
Mouth
(a) Lancelet in the sand
Pharyngeal slits
Intestine
Atriopore
Muscles
Anus
Postanal tail
(b) Body plan of the lancelet
a: © Natural Visions/Alamy

86. Subphylum Urochordata
 Tunicates – animal encased in tunic
 3,000 marine species
 Adult is sessile with only pharyngeal slits
 Larvae tadpole-like exhibiting all 4 chordate
hallmarks
 Closest living relatives of vertebrates
 Cephalochordates more closely related to
echninoderms
 Filter feeders with two siphons 86

87. Ciliated pharynx
Excurrent siphon
Anus
Intestine
Postanal tail Notochord
 Rudimentary circulatory system
 Simple nervous system
 Mostly hermaphroditic
87
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Water
Incurrent siphon
Tunic
Pharyngeal slits
Heart
Stomach
(c) Typical tunicate
Stolons
(a) Adult tunicate
Dorsal hollow
nerve cord
Excurrent
siphon
Incurrent
siphon
Pharyngeal
slits
Stomach Heart
(b) The larval form of the tunicate
c: © Reinhard Dirscherl/Visuals Unlimited.