Invertebrates

Invertebrates

Nearly all animals are invertebrates (95%)

Invertebrates are animals that lack backbones

Let’s take a survey of the major phyla of animals!

Major Animal Phyla

Chordates

Echinoderms

Arthropods

Annelids

Mollusks

Rotifers

Roundworms

Flatworms

Cnidarians

SpongesMulticelled Ancestry

Radial Ancestry

Bilateral Ancestry

Coelomate Ancestry

Single-celled, protistanlike ancestorsFigure 25.2Page 415

Symmetry

Radial Bilateral Figure 25.3Page 416

dorsal

posterior

ventral

anterior

The Gut

Region where food is digested and then absorbed

Saclike gut One opening for taking in food and

expelling waste Complete digestive system

Opening at both ends; mouth and anus

Body Cavities - Acoelomate

epidermisgut cavity

no body cavity; region between gut and body wall packed with organs

Figure 25.4aPage 417

Body Cavities - Pseudocoel

epidermis gut cavity

unlined body cavity (pseudocoel) around gut

Figure 25.4bPage 417

Body Cavities - Coelom

gut cavity

peritoneumlined body cavity (coelom) Figure 25.4c

Page 417

Segmentation

Repeating series of body units Units may or may not be similar to

one another Earthworms - segments appear

similar Insects - segments may be fused

and/or have specialized functions

Animal Origins

Originated during the Precambrian (1.2 billion - 670 million years ago)

From what? Two hypotheses: Multinucleated ciliate became

compartmentalized

Cells in a colonial flagellate became specialized

Phylum Porifera Representative organism: sponge Have no true tissues (Parazoa)

Their cells are relatively unspecialized Sponges are sessile (nonmotile)

Ancient Greeks believed them to be plants Filter-feeders:

Trap food from the water that flows through them

Most sponges are hermaphrodites

Each individual produces both sperm and eggs

Sponge Structure

central cavity

water out

water in

flagellum microvilli nucleus

glasslike structural elements

amoeboid cell

pore

semifluid matrix

flattened surface cells

Figure 25.7aPage 419

Phylum Cnidaria Have stinging

cells inside of nematocysts

On tentacles

Figure 25.8Page 420

barbed thread inside capsule

capsule’s lid at free surface of epidermal cell

trigger

nematocyst

Phylum Cnidaria Representative Organisms:

Jellyfish & Sea Anemones Have true tissues and radial

symmetry Body plan: sac with a central

digestive compartment known as the gastrovascular cavity (mouth & anus)

2 variations on the body plan: Polyp: sessile, mouth up, waits

for prey (sea anemone) Medusa: floats, mouth down

(jellyfish) Attack prey with tentacles

33-06b-JellySwimming-B.mov

Two Main Body Plans

Figure 25.9 Page 420

outer epithelium (epidermis)

mesoglea(matrix)

inner epithelium (gastrodermis)

Medusa

Polyp

Obelia Life Cycle (Hydrozoan)

reproductivepolyp

female medusa male medusa

sperm

zygote

ovum

planula

polyp forming

feeding polyp

Figure 25.10Page 421

Phylum Platyhelminthes

Representative Organisms: Tapeworms, flukes,

& planarians Bilateral symmetry Acoelomates –

no body cavity enclosed by mesoderm

Many are parasitic

Planarian Organ Systems

pharynx

protonephridia

flame cellnucleus

cilia

fluid filters through membrane foldsflame cell

opening of tubule at body surface

Fig. 25.11a,bPage 422

Planarian Organ Systems

brain nerve cord

genital poreoviducttestisovary

penis

Fig. 25.11cdPage 422

Flukes: Class Trematoda

Parasitic worms

Complicated life

cycle

Larval stage

infects a mollusk

Adult infects a

vertebrate

Ciliated larva

Worms mate in human host

Fertilized egg

Asexual reproduction in intermediate host

Larvae form, leave snail

Larvae bore into human skin

Southeast Asian blood fluke Figure 25.14Page 424

Tapeworms: Class Cestoda

Larvae encysted in muscle tissue

Intermediate host Mature proglottid with fertilized eggs

Scolex attaches to host intestinal wall

Definitive host

Figure 25.15Page 424

Phylum Nematoda

Representative organism: roundworms

Pseudocoelomate have a body cavity,

but not encased by mesoderm

Round worms with tapered ends

Can be parasitic (trichinosis)

Roundworms (Nematoda)

False coelom (pseudocoelomate) Complete digestive system

gonadpharynx intestine

false coelom

eggs in uterus anus

muscularized body wall

Figure 25.13Page 423

Two Coelomate Lineages

Protostomes

Mollusks

Annelids

Arthropods

Deuterostomes

Echinoderms

Chordates

Cleavage Patterns

Protostome embryo(spiral cleavage)

Blastopore becomes mouth

Deuterostome embryo(radial cleavage)

Blastopore becomes anus In-text figure

Page 426

Phylum Mollusca

Representative organisms: snails, slugs, oysters,

clams, octopuses, squids

Coelomates Have a true coelom

Protostomes: Blastopore becomes

mouth

Phylum Mollusca Body plan has 3 main

parts: Muscular foot used for

movement Visceral mass

covering the internal organs

Mantle covers the visceral mass (may produce a protective shell)

Cuttlefish Body Plan

Closed circulatory system with heart and accessory heart

stomachkidneyesophagus

digestive gland

brain

arm

jaw

tentacle radula

siphon

anusink sac

gillheart accessory

heart

reproductive organ

mantleinternal

shell

Figure 25.22Page 429

Phylum Annelida Representative Organism:

earthworm Annelids have segmented

bodies Metanephridia (similar to

kidneys) Remove wastes from the

blood Worms are hermaphrodites

Produce both sperm and eggs Setae provide traction for

burrowing in the soil Earthworms eat their way

through the soil

33-23-EarthwormLocomot-B.mov