1. Lecture Topics What is an animal? Evolutionary trends in animals
Introduction to some representative animal phyla

2. What is an Animal?
Animals are very diverse but do share some general common characteristics
Multicellular heterotrophic eukaryotes
Ingest food
Diploid
Capable of locomotion
Reproduce sexually, but asexual reproduction is common
Lack cell walls
Appear to be a monophyletic group

4. Evolutionary trends Germ Layers – embryonic cell layers
Begin with single undifferentiated layer
E.g., Porifera
Diploblastic – two germ layers:
E.g., Cnidaria
Ectoderm (outer) Skin & nerves
Endoderm (inner) Gut
Triploblastic – adds a third germ layer
E.g., Arthropoda
Mesoderm (middle) Muscle, many organs

5. Evolutionary trends Digestive tract Begins with no digestive tract
E.g., Porifera
Blind sac with food in and waste back out
E.g., Cnidaria
One way gut – tube within a tube
E.g., Annelida

6. Triploblastic Body Plans
Acoelomates
Solid body construction
Pseudocoelomates
Lined on only outer side with mesoderm
No mesentery
Coelomates
Completely surrounded by mesoderm
Mesentery suspends gut from body wall

7. Evolutionary trends Body symmetry Asymmetry = None
Porifera
Radial symmetry = Symmetric (mirror image) about oral-aboral axis
Cnidaria (mostly?)
Bilateral symmetry = Symmetric only about one plane
Pretty much everything else

8. Sections, Directions, and Symmetry

9. Evolutionary trends Cephalization -- formation of a distinct head
Associated with Bilateral symmetry
Puts sensory organs and mouth in the lead
Generally considered an adaptation for an active lifestyle
Contrast Porifera, Cnidaria, Echinodermata with Annelida and Arthropoda

10. Segmentation, Metamerism, and Tagmatization or Tagmosis
Segmentation – division of body into distinct segments able to operate independently of one another
Metamerism – serial repetition of body parts
Contrast Nematoda vs Annelida or Arthropoda
Tagmatization – organization of segments into functional units (e.g., head, thorax, abdomen)
Contrast Annelida vs. Arthropoda

12. Sponges: Phylum Porifera
Germ Layers – None – Very loosely organized – can sift cells and will regenerate
Digestive tract – None – Choanocytes filter food from water, amebocytes transfer nutrients
Coelom – None
Symmetry – None
Segmentation – None

13. Unique Structures Spicules – Silica or calcium carbonate
Spongin – Flexible protein
Choanocytes – Collar cells – similar to choanoflagellates
Drive water flow in ostia and out osculum

14. Figure 28-6b Page 542 Osculum Epidermal cell Spongocoel Incurrent
pores
Porocyte
Water movement
Spicule
Collar cell
Amoeboid cell
in mesohyl
Microvillus
Flagellum
Nucleus
Figure 28-6b Page 542
Collar

24. Jellyfish, Anemones, Corals, Hydra : Phylum Cnidaria or Coelenterata
Germ Layers – Two, with gelatinous mesoglea between endoderm and ectoderm
Digestive tract – Blind sac – food enters and exits through mouth
Coelom – None
Symmetry – Radial
Segmentation – None

25. Unique Structures
Cnidocytes with Nematocycts – Stinging cells with venomous harpoons
Polyp – Sessile form e.g., Anemone, Hydra
Medusa – Swimming form, e.g., Jellyfish

36. Two major clades of animals: Protostomes vs. Deuterostomes
Embryonic origin of gut
Protostome = First Mouth – Mouth arises from blastopore – first invagination of blastula (hollow ball of embryonic cells)
Deuterostome = Second mouth – Anus arises from blastopore
Early development
Protostomes – Determinate, spiral cleavage, coelom originates from solid mass of cells
Deuterostomes– Indeterminate, radial cleavage, coelom originates as pouches off gut

37. Fig. 32.3

38. Phylogeny undergoing revision
Protostomes now divided into two clades
Spiralia
Ecdysozoa (animals that molt)
Flatworms previously considered separate clade -- Acoelomates
Nematodes and rotifers previously considered pseudocoelomates (not protostome coelomates) but molecular evidence suggests protostome ancestry (details change with new data)
Now flatworms, nematodes, and rotifers considered simplified coelomates
Flatworms in Platyzoa within Spiralia
Nematodes in Ecdysozoa

40. Segmented Worms: Phylum Annelida
Germ Layers – Three
Digestive tract – One way gut
Coelom – True coelom
Symmetry – Bilateral
Segmentation – Yes, with metamerism

47. Snails, Bivalves, Cephalopods: Phylum Mollusca
Germ Layers – Three
Digestive tract – One way gut
Coelom – True coelom with mesentery – lined with mesoderm on both inner (gut) and outer (body wall) surfaces
Symmetry – Bilateral
Segmentation -- ? Chitons have serial plates

48. Unique Structures Radula – Rasping structure on “tongue”
Calcium carbonate shell (absent in slugs, internal in most cephalopods) secreted by mantle

56. Giant squid Architeuthis dux
World’s largest invertebrate (18m, 900kg)

63. Ecdysozoa Protostomes that molt
Arthropods – Rulers of the planet! (insects, spiders, crustaceans, etc.)

64. Insects, Arachnids, Crustaceans, Myriapods, etc.: Phylum Arthropoda
Germ Layers – Three
Digestive tract – One way
Coelom – True coelom
Symmetry – Bilateral
Segmentation – Yes, with tagmatization (head, thorax and abdomen or cephalothorax and abdomen or
head and trunk)

66. Unique Structures Jointed Appendages
Chitinous exoskeleton (remember chitin?…)
Wings (insects)
Chelae (crabs)

76. Photographer: Alan Gornick Jr.
©Aris Multimedia Entertainment, Inc. 1994

85. Deuterostomes
Echinoderms
Chordates

87. Phylum Echinodermata Germ Layers: Three Digestive tract: One way
Coelom
Symmetry: Bilateral (“pentaradial”)
Segmentation: In arms?

88. Unique Structures Water vascular system with tube feet
Pedicellaria -- tiny pincers on flexible stalks
Dermal skeleton of calcium carbonate

89. Figure 30-2 Page 577 Digestive gland Stomach Gonad Digestive gland
Tube feet
Tube feet
Anus
Ampulla
Gonad
Spine
Dermal gill
Pedicellariae
5 mm
Tube feet
Figure 30-2 Page 577

93. Phylum Chordata Very successful Includes 3 subphyla, some invertebrate
Urochordata – tunicates
Cephalochordata – lancelets
Vertebrata

94. 2 out of 3 chordate subphyla are invertebrates
Chordata
2 out of 3 chordate subphyla are invertebrates
Echinodermata
sea urchins)
(sea stars,
Cephalochordata
(lancelets)
Hemichordata
(acorn worms)
Urochordata
(tunicates)
Vertebrata
Cranium,
vertebral
column
Notochord,
dorsal tubular nerve cord,
pharyngeal slits,
postanal tail
Deuterostome
ancestor

95. Tadpole Larva

99. Figure 30-6 Page 581 Chordata Cephalochordata Echinodermata
sea urchins)
(sea stars,
Cephalochordata
(lancelets)
Hemichordata
(acorn worms)
Urochordata
(tunicates)
Vertebrata
Figure 30-6 Page 581
Deuterostome
ancestor

100. Subphylum Cephalochordata: The Lancelet or Amphioxus Branchiostoma sp.
Tentacles
Nerve
cord
Notochord
Gill slits
Intestine
Caudal fin
Tentacles
Endostyle
Atrium
Gonads
Atriopore
Anus

101. Craniates
V e r t e b r a t e s
Jawless fishes
Amniotes
Cephalaspidomorphi
(lampreys)
(cartilaginous fishes)
Chondrichthyes
(ray-finned fishes)
Actinopterygii
Cephalochordata
(lancelets)
Urochordata
(tunicates)
(hagfishes)
Myxini
(coelacanths)
Actinistia
(lungfishes)
Dipnoi
Mammalia
Amphibia
Reptilia
(birds)
Aves
Amniotic egg
Limbs
Lungs (for swim
bladder)
Jaws
Vertebrae
Chordate
ancestor