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Invertebrate Evolution
Chapter 18
Defining Animals
• Invertebrates
– majority
• Vertebrates
• Commonality
– Multicellular eukaryotes
– Chemoheterotrophs
• Obtain food through ingestion
– Diploid (2n) organisms reproduce sexually
– Nonliving substances produced
• Facilitate movement
• Provide support
Classifying Animals
• ‘Body plans’ used for
morphologically based
phylogenetic trees
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Tissue organization
Symmetry
Embryonic development
Body cavity
• Hypotheses only
– DNA discoveries maintain
constant restructuring
Kingdom Animalia
Tissue Organization
 2 or 3 layers of cells
 Diplo- or triploblastic
 Phylum Porifera excluded
 Gastrulation of blastula forms germ
layers
 Endoderm = digestive tube, liver, and
lungs
 Ectoderm = outer covering and some
nervous systems
 Mesoderm = muscles and bone
Symmetry
 Asymmetry
 Most sponges
 Radial symmetry
 Top and bottom, but no front, back,
or sides
 Sessile or drifts
 Bilateral symmetry
 Anterior and posterior, dorsal and
ventral
 Most demonstrate cephalization
 Motile with complex movements
Embryonic Development
• 3 germ layer animals
• Based on fate of gastrula
– Deuterostomes
• Chordates and echinoderms
– Protostomes
• All others
Body Cavities
 Only bilateral, 3 germ layer
animals
 Presence or absence of a fluid
filled space called a coelom
 Coelomates
 Pseudocoelomates
 Acoelomates
 Allows independent organ
movement and growth
 Hydrostatic skeleton
Phylum Porifera (Sponges)
 Asymmetrical, sessile, aquatic animals
 Suspension feeders
 Water
pores
osculum
 Cellular organization
 Choanocytes move water in
 Traps food in mucus
 Amoebocytes digest food and produce
skeletal support
 Spicules: mineralized material
 Spongin: flexible protein
 No muscles or nerves
 Hermaphrodites
 Reproduce by budding of fragmentation
 Produce toxins for protection
 Used for antibiotics
Phylum Cnidaria (Cnidarians)
 Radial symmetry
 Polyp, medusa, or both
 Diploblastic with inner mesoglea
 Creates hydrostatic skeleton
 Single opening to a
gastrovascular cavity = sac plan
 Simplistic muscles and nerve net
 Facilitates movement
 Cnidocytes in tentacles to
capture and immobilize prey
Phylum Platyhelminthes (Flatworms)
 Bilateral, triploblastic, acoelomate, sac plan
 Planarians (free-living)
 Simple brain, eyespots, auricles, and
branched gastrovascular cavity
 Live on underside of rocks in freshwater
 Flukes (animal parasites)
 Suckers and interior almost all reproductive
organs
 Larval intermediate stage
 Pinch in half to reproduce
 Tapeworms (animal parasites)
 Scolex, no mouth (absorption),
hemaphrodites, eggs released from end
(proglottids) in feces
 Larval intermediate in prey species develop
into adults in predators
Phylum Nematoda (Roundworms)
• Pseudocoelomate, tube within a tube plan, separate
hookworms
sexes, and lateral muscles
• Can shed cuticle, outer covering when grows
• Free-living decomposers in soil (C. elegans)
Trichinella
• Parasitic
– Dog heartworm
• Mosquito vector
– Trichinella spiralis
heartworms
• Uncooked pork
– Pinworms
– Hook worms
pinworms
Phylum Mollusca (Molluscs)
 Coelomates with 3 part body plan
 Foot: muscular organ for locomotion,
attachment, or feeding
 Visceral mass: contains internal organs
 Mantle: surrounds visceral mass and
may secrete shell; cavity for gills or lungs
 Feed via a radula
 Most separate sexes, except snails
 Open circulatory system, blood not
confined to vessels (except cephalopds)
 Neural ganglia connected by nerve cord
 Advanced sensory systems in cephalopods
Mollusc Classes
 Class Gastropoda (snails and slugs)
 Head w/ eyes
 Only terrestrial species; no gills
 Class Cephalopoda (squids and
octopuses)
 Mouth at end of foot, shell small or absent
 Most advanced invertebrate brain and
sense organs (eyes)
 Siphon for steering movements
 Class Bivalva (scallops, oysters, and
clams)
 Paired hinged shells
 Suspension feeders
 Mantle with gills
Phylum Annelida (Segmented Worms)
 Segmentation
 Longitudinal and circular muscles
 Closed circulatory system
 Class Oligochaeta (earthworms)
 Hermaphroditic, exchange sperm
 Solid ventral nerve cord, anterior brain, and a ganglia
in each segment
– Nephridia for excretion
– Unsegmented, compartmentalized digestive system
 Nutrients diffuse across body wall
Annelida Classes (Cont.)
 Class Polychaeta
 Largest class
 Marine organisms
 Segmented appendages for mov’t or gills
 Live in tubes of mucus and sand
 Class Hirudinea (leeches)
 Blood-sucking
 Release an anesthetic and anticoagulant
 Consume 10X’s weight
 Medicinal uses
Phylum Arthropoda (Arthropods)
 Most successful phylum (1,000,000+ species)
 Exoskeleton (hydrostatic earlier)
 Cuticle of protein and chitin for protection and joint attachment
 Molted with growth, eaten for nutrients
 Segmentation
 Head, thorax (fused is cephalothorax), and abdomen
 Sensory, protection and walking, and swimming respectively
 Jointed appendages
 Open circulatory system
 Gas exchange
 Aquatic  gills
 Terrestrial  spiracles
 Advanced sensory systems
Arthropd Linneages
• Chelicerates (arachnids)
– First terrestrial carnivores
– Hollow mouth appendages; may deliver venom or toxins
– E.g scorpions (night), spiders (day), and ticks/mites
• Millipedes and centipedes
– Herbivores with 2 leg sets per segment
– Carnivores (poisonous) with 1 leg set per segment
• Crustaceans
• Insects
– 70+ % all known animal species
– Unrivaled evolutionary success
• Flight
• Waterproof cuticle
• Life cycle complexity
Class Insecta
 Life cycles
 Complete and incomplete metamorphosis
 Larvae and adult with different roles
 Only adults can reproduce or have functional wings
 Food sources differ  enhances adaptability
 Body plan
 3 parts: head, thorax, and abdomen
 Embryonic segments develop independently
 3 pairs of legs, wings not at cost to legs
 Mouthparts for food sources  few limits
 Coloration
 Camouflage, mimicry, and coloration from independent
development
 Gene regulation role
Phylum Echinodermata
• External radial symmetry as an adult,
bilateral as larvae
• Ca2+ plates form endoskeleton
• Locomotion, feeding, and gas exchange via
tube feet
– Water vascular system
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Mouth and stomach adaptations
Capable of regeneration
Deuterosomes
Include sea stars, urchins, and same dollars