1. Biology, 9th ed, Sylvia Mader
Chapter 29
Chapter 29
Introduction to Invertebrates
Introduction to Invertebrates

2. Animals
What makes an animal? How can you tell if something is an animal or not? What are some examples of animals?

3. Evolution of Animals (intro)
All animals are multicellular heterotrophic organisms that must take in preformed food.
mulitcellular: made of more than one cell
heterotrophic: take in preformed food from other organisms
food: complex organic molecules; often glucose related compounds

4. Criteria for the Evolution of Animals 1. Multicellularity
Outline
Criteria for the Evolution of Animals
1. Multicellularity
2. True Tissues
3. Bilateral Symmetry
4. Body Cavities
5. The Coelom
6. Segmentation
7. Development

5. Evolution of Animals (intro)
All animals are multicellular heterotrophic organisms that must take in preformed food
Classification Criteria
Level of organization
Cellular, tissue, organ
Body Plan
Sac, tube-within-a-tube
Segmentation
Segmentation leads to specialization

6. Evolution of Animals (intro)
Classification Criteria, cont
Symmetry
Radial - Two identical halves
Bilateral - Definite right and left halves
Type of Coelom
Acoelomate
Pseudocoelom
Coelom
Early Developmental Pattern
Protostome - First embryonic opening becomes the mouth
Dueterostome - Second embryonic opening becomes the mouth

7. Animals: How does this picture demonstrate that an animal is involved?

8. Traditional Phylogenetic Tree of Animals

9. Animal?
In order to be considered an animal, what must be true about this organism?

10. Multicellularity Sponges
Only level of animal to have cellular organization
Saclike bodies perforated by many pores
Beating of flagella produces water currents that flow through pores into central cavity and out osculum
Sessile filter feeders
Asexual reproduction by fragmentation or budding

11. Simple Sponge Anatomy

12. Porifera in the Animal Cladogram
Sponges sitting at the bottom of the animal phylogeny simplest of the existing animals and possibly one of the simplest of all time

13. True Tissue Layers – Ctenophora & Cnidarians
Many animals have a total of three possible germ layers
Ectoderm – outside layer; skin or outer covering , brain and peripheral nerves
Endoderm – inside layer; gut track and some digestive tissues
Mesoderm – inner layer; muscles
phlya Ctenophora and Cnidaria develop only ectoderm and endoderm
Diploblasts – animals derived from only 2 embryonic layers
Radially symmetrical

14. True Tissue Layers
phlya Ctenophora and Cnidaria develop only ectoderm and endoderm
So what is in the middle if these organisms (the first with true tissue layers) ?
What are Ctenophora called again?

15. Types of Symmetry

16. Comb Jellies - Ctenophora
Characteristics:
Small, transparent, and often luminescent
Most of body composed of mesoglea
Largest animals propelled by beating of cilia
Capture prey with tentacles

17. Comb Jelly Compared to Cnidarian

18. Tubular animals that most often reside in shallow marine waters
Cnidarians
Tubular animals that most often reside in shallow marine waters
Polyp and medusa body forms
Specialized stinging cells (cnidocytes)
Fluid-filled capsule, nematocyst
Two-layered body sac
Outer layer - Protective epidermis
Inner layer - Gastrovascular cavity
Nerve net found throughout body

19. Cnidarian Diversity

20. Hydra Freshwater cnidarian
Small tubular poly body about one-quarter inch in length
Gastrovascular cavity is central cavity
Tentacles can respond to stimuli
Can reproduce sexually and asexually

21. Anatomy of Hydra

22. A colony of polyps enclosed by a hard, chitinous covering. Chitin?
Obelia
A colony of polyps enclosed by a hard, chitinous covering. Chitin?
Feeding polyps
Extend beyond covering
Have nematocyst-bearing tentacles
Reproductive polyps
Budding of new polyps
Also has sexual reproduction (medusae) stage

23. Obelia Life Cycle

24. Ctenophora and Cnidarians
Where are we now? How are cnidarians and ctenophora different from sponges? What new “feature” do they posses that sponges did not have?

26. Bilateral Symmetry
New Characteristics
Bilateral Symmetry
animals have a “left and right”
one plane of symmetry
Cephalization
identifiable or obvious “head” end of the animal
having mouth and/or sensory organs at one end

27. Bilateral Symmetry
Pseudocoelomates
Both phyla today will be considered pseudocoelomates
What is the difference between acoelomates, pseudocoelomates and coelomates (or eucoelomates?)

28. Bilateral Symmetry
Coelomates (also known as eucoelomates — "true coelom") have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers).
Pseudocoelomate  have a pseudocoel (literally “false cavity”), which is a fully functional body cavity. Tissue derived from mesoderm only partly lines the fluid filled body cavity of these animals. Thus, although organs are held in place loosely, they are not as well organized as in a coelomate.
Acoelomate animals, like flatworms, have no body cavity at all. Organs have direct contact with the epithelium. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.

29. Bilateral Symmetry Flatworms (phylum Platyhelminthes)
Majority are parasitic
Organ-level organization
No specialized circulatory or respiratory structures
Have undergone cephalization
Ladder-type nervous system
Ribbon worms (phylum Nemertea)
Have distinctive proboscis
Have a complete gut track

30. Belong to the phylum platyhelminthes. (Plat = flat)
Flatworms
Belong to the phylum platyhelminthes. (Plat = flat)
There are three classes:
Turbellaria
Trematoda
Cestoda

31. Characteristics of Flatworms
They are acoelomates (they don’t have body cavities)
They have bilateral symmetry
Show cephalization
Respiration through skin
Single opening to digestive tract (pharynx)

32. Free-living Flatworms
Planarians (genus Dugesia)
Live in freshwater habitats
Head is bluntly arrow shaped
Auricles function as sense organs
Two light-sensitive eye spots
Three kinds of muscle layers:
Outer circular layer
Inner longitudinal layer
Diagonal layer

33. Planarian Anatomy

36. Planarians Planarians, cont.
Excretory organ functions in osmotic regulation and water excretion
Can reproduce asexually
Hermaphroditic
Practice cross-fertilization

37. Parasitic flatworms are flukes (trematodes) and tapeworms (cestodes)
Well-developed nerves and gastrovascular cavity are unnecessary
Flukes
Reproductive system well developed
Usually hermaphroditic

38. Life Cycle of Schistosomiasis

39. Parasitic Flatworms Tapeworms
Have anterior region with modifications for attachment to intestinal wall of host
Behind head region, scolex, a long series of proglottids are found
Segments each containing a full set of both male and female sex organs
Complicated life cycles

40. Life Cycle of a Tapeworm, Taenia

41. Class Trematoda Are parasitic flukes
Have suckers on both ends of the body
Can live inside or outside of host
Not much cephalization

42. Class Trematoda Nervous and excretory systems like turbellarians
Hermaphrodites
Have complex life cycles

43. Class Cestoda Parasitic Tapeworms Long, ribbon-like bodies
Absorbs nutrients from host
Hermaphrodites

44. Tapeworm Anatomy

48. Ribbon Worm, Lineus

49. Phylum Nemertea (Rhynchocoela) Ribbonworms
The nemerteans (ribbon worms) are long, marine predatory worms and there are about 1000 species known.
Unlike members of the Platyhelminthes nemerteans have a complete gut with a mouth and anus and a true circulatory system

50. Phylum Nemertea (Rhynchocoela) Ribbonworms
Prey is captured using a long muscular proboscis armed with a barb called a stylet..
The proboscis lies in an interior cavity called the rhynchocoel and muscular pressure on fluid in the rhynchocoel causes the proboscis to be quickly everted.
The prey is wrapped in the sticky, slime-covered, proboscis and stabbed repeatedly with the stylet. Neurotoxins in the slime incapacitate the prey.

51. 8.18 Internal structure of female ribbon worm (left).
Nemertean with proboscis extended (below)
8.18

52. Baseodiscus mexicanus a nemertean from
8.19
Baseodiscus mexicanus a nemertean from
the Galapagos Islands

53. Pseudocoelom
What is different about the animals we discussed today?
How are flatworms (Platyhelminthes) different from cnidarians?
How are nemertea (ribbon worms) different from flatworms?

54. Pseudocoelom Pseudocoelom:
A “false” body cavity that is incompletely lined by mesoderm
Provides a space for internal organs and can serve as hydrostatic skeleton
Both phyla today are animals with a complete body gut track and pseudo coelom
phylum Nematoda and Rotifera

55. Types of Body Cavities
3 types of body cavities

56. Types of Body Cavities
acoelomate

57. Types of Body Cavities
pseudocoelomate

58. Types of Body Cavities
Coelomates – not
there yet

59. Roundworms (phylum Nematoda)
Pseudocoelom 59
Roundworms (phylum Nematoda)
Non-segmented, generally colorless worms
Several parasitic roundworms infect humans

60. Roundworm Anatomy

61. Parasitic Roundworms
Ascaris – Intestinal roundworm
Trachinella - Trichinosis
Dirofilaria - Heartworms
Wuchereria - Elephantiasis

62. Filarial Worm

63. Rotifers (phylum Rotifera)
Named for crown of cilia resembling a rotating wheel
Serves as both as an organ of locomotion and aids direction of food to mouth
Important base of many ecosystems
Planktonic
Transparent organisms
Can survive dessication

64. Rotifer

65. Rotifers on youtube.com
25X Magnification

66. Pseudocoelomates
How are nematoda and rotifera different from platyhelminthes and nemertea (flatworms and ribbon worms?)