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

Kingdom Animalia

• ‘Body plans’ used for morphologically based phylogenetic trees– Tissue organization– Symmetry– Embryonic development– Body cavity

• Hypotheses only– DNA discoveries maintain

constant restructuring

Tissue Organization

2 or 3 layers of cellsDiplo- or triploblasticPhylum Porifera excluded

Gastrulation of blastula forms germ layersEndoderm = digestive tube, liver, and

lungsEctoderm = outer covering and some

nervous systemsMesoderm = muscles and bone

Symmetry

AsymmetryMost sponges

Radial symmetryTop and bottom, but no front,

back, or sidesSessile or drifts

Bilateral symmetryAnterior and posterior, dorsal and

ventralMost demonstrate cephalizationMotile with complex movements

Embryonic Development

• 3 germ layer animals• Based on fate of gastrula– Deuterostomes

• Chordates and echinoderms

– Protostomes• All others

Body CavitiesOnly bilateral, 3 germ layer

animalsPresence or absence of a fluid

filled space called a coelomCoelomatesPseudocoelomates Acoelomates

Allows independent organ movement and growthHydrostatic skeleton

Phylum Porifera (Sponges)

Asymmetrical, sessile, aquatic animalsSuspension feeders

Water pores osculumCellular 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 nervesHermaphrodites

Reproduce by budding of fragmentationProduce toxins for protection

Used for antibiotics

Phylum Cnidaria (Cnidarians)Radial symmetry

Polyp, medusa, or bothDiploblastic with inner mesoglea

Creates hydrostatic skeletonSingle opening to a

gastrovascular cavity = sac planSimplistic muscles and nerve net

Facilitates movement

Cnidocytes in tentacles to capture and immobilize prey

Phylum Platyhelminthes (Flatworms)Bilateral, triploblastic, acoelomate, sac planPlanarians (free-living)

Simple brain, eyespots, auricles, and branched gastrovascular cavity

Live on underside of rocks in freshwaterFlukes (animal parasites)

Suckers and interior almost all reproductive organs

Larval intermediate stagePinch 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

sexes, and lateral muscles• Can shed cuticle, outer covering when grows• Free-living decomposers in soil (C. elegans)• Parasitic – Dog heartworm

• Mosquito vector– Trichinella spiralis

• Uncooked pork– Pinworms– Hook worms

hookworms

heartworms

pinworms

Trichinella

Phylum Mollusca (Molluscs)Coelomates with 3 part body plan

Foot: muscular organ for locomotion, attachment, or feeding

Visceral mass: contains internal organsMantle: surrounds visceral mass and

may secrete shell; cavity for gills or lungsFeed via a radulaMost separate sexes, except snailsOpen 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/ eyesOnly terrestrial species; no gills

Class Cephalopoda (squids and octopuses)Mouth at end of foot, shell small or

absentMost advanced invertebrate brain and

sense organs (eyes)Siphon for steering movements

Class Bivalva (scallops, oysters, and clams)Paired hinged shellsSuspension feedersMantle with gills

Phylum Annelida (Segmented Worms)

SegmentationLongitudinal and circular musclesClosed circulatory systemClass Oligochaeta (earthworms)

Hermaphroditic, exchange spermSolid 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 classMarine organismsSegmented appendages for mov’t or gillsLive in tubes of mucus and sand

Class Hirudinea (leeches)Blood-sucking

Release an anesthetic and anticoagulantConsume 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 attachmentMolted with growth, eaten for nutrients

SegmentationHead, thorax (fused is cephalothorax), and abdomen

Sensory, protection and walking, and swimming respectivelyJointed appendagesOpen circulatory systemGas exchange

Aquatic gillsTerrestrial 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 InsectaLife cycles

Complete and incomplete metamorphosisLarvae and adult with different roles

Only adults can reproduce or have functional wingsFood sources differ enhances adaptability

Body plan3 parts: head, thorax, and abdomenEmbryonic segments develop independently

3 pairs of legs, wings not at cost to legsMouthparts for food sources few limits

ColorationCamouflage, mimicry, and coloration from independent

developmentGene 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

• Mouth and stomach adaptations• Capable of regeneration• Deuterosomes• Include sea stars, urchins, and same dollars