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