Chapter 33

Lack a backbone95% of known animal speciesOccupy almost every habitat on

Earth

No True tissuesNo symmetrySuspension feedersMost are hermaphroditic

Radial symmetryAll have cnidocytesDiploblasticGastrovascular cavity (no anus)CarnivorousBody plan:

PolypMedusa

Simple muscle systemSimple nerve net nervous system,

no brain

HydrozoaAlternate polyp and medusa in life cyc

le, with polyp as dominant stageExamples: colonial hydroids, hydra, P

ortuguese Man of WarScyphozoa:

Prominent medusaExamples jellyfish

Anthozoa:Polyps are dominantSea anemonies, and coral

Lack coelomBilateral symmetryWhat evolutionary novelty comes

with bilateral symmetry?Cephalization

What new novelties are seen in this phylum?

Triploblastic, so has muscular system

OrgansCephalization, more complex

nervous system

Turbellaria:CarnivorousMoves by ciliaEyespots on headRudimentary brainDiffusion for gas exchangeExcretion through flame cellsHermaphroditic

                                                                             

Often called flukesAll members are parasiticWhat makes a parasite in good

standing?Become an egg machine since it is

hard to find a hostUse intermediate hostsDevelop hooks and suckersHermaphroditism, so that limits need

to find others

TapewormsParasiticScolex in adult hooks onto the

host intestinesProglottids for reproductionEggs eaten by intermediate host

and larva developsFinal host infected by eating

intermediate host encysted with larva forms

Do not eat poorly cooked meats!

Not quite a true coelom, missing the inner lining of muscle

Mostly marine1st to get an anusOrgans lie in the pseudocoelomParthogenesis – unfertilized eggs develop into females

Many found in soil, useful for nutrient recycling

Complete digestive tractSome are parasitic, e.g. trichinella

and hookworm (dogs)

Mouth develops from the blastoporeCleavage is radial and determinateALL HAVE A TRUE COELOM!

Bilateral symmetryOpen circulatory systemSoft bodied, with hard shell protectionMost have exoskeletonsReduced or no segmentationRadula; rasping tongue to scrape foodTrue coelomMany internal organsThree body parts

FootVisceral massMantle

Polyplacophora ChitonsCling to rocksLive on rocky shoresUse muscular foot to grip

GastropodsSnails, slugs, nudibranchsLargest classShell protects bodyTorsion leads to twisted bodyUses radula to scrape algae and graze

on plants

Bivalves:Clams, oysters, mussels, scallopsPossess shell divided and hinged into two halve

sFilter feedersSedentary lifestyle

CephalopodsSquid and octopus and nautilusUse jaws to bite preyMouth as base of foot (foot drawn into several t

entacles)Complex brains and capable of learning and m

oving fastMantle reduced or absentCan get large, How?

SEGMENTATION!Closed circulatory systemAlimentary canalFive pairs of heartsGas exchange across skinMetanephridia for gas exchangeNitrogenous wastes exit from each segment

through poresNervous system with ganglia and ventral

nerve cords

OligocheatesEarthworms

Polycheates:FanwormsTube dwellers (marine)

Hirudinea:LeechesUsed to treat bruised tissues and to s

timulate circulation

Coelom Serves as hydrostatic skeletonDeveloped complex organ systemProtects internal structures

SegmentationSpecialization of body segments

Key characteristics:Jointed appendagesSegmentationHard exoskeletonsExtensive cephalizationOpen circulatory systemGas exchange gills in water,

book lungs or spiracles on land

Successes:Exoskeleton, lets them thrive on land,

but limitedJointed appendages allowed for

walking and then flying in someMore successful organization of

segmentsLimits:

Exoskeleton is shedLimited brain sizeLimited body size

TrilobitesExtinct groupShow pronounced segmentation, with

little variation in appendagesEarly, primitive arthropods

CheliceratesIncludes the arachnids1-2 body segments with 8 legs

UniramiaIncludes insects, millipedes and

centipedes

ArachnidsScorpions, spiders, mites

Insects 1 pair of antennae6 legs3 body segments

CrustaceansCrabs, crayfish, lobsters, isopods (pill bugs)2 or 3 body segments

Radial indeterminate cleavageBlastopore becomes the anus

Secondarily evolved radial symmetryUnique water vascular systemHas mouth and anusHas endoskeleton

AseroideaSea stars

OphiuroideaBrittle stars

EchinoideaSea urchins and sand dollars

HolothuroideaSea cucumbers

Phylum Annelida

Phylum Cnidaria

Phylum Mollusca

Phylum Echinodermata

Phylum Arthropoda

Phylum Nematoda

Phylum Platyhelminthes

Phylum Porifera

. . . the exoskeleton

. . . none

. . . segmentation

. . . it is one way; having both a mouth and an anus

. . . bilateral symmetry and cephalization

. . . radial symmetry

. . . the coelom

                                      

                                      

                                      

                   

                         

                                                                             

                                                                                                     

                                      

                                      

An open circulatory

system limits the size of these

animals

The closed circulatory system is

much more efficient!