Invertebrates

Animal Characteristics• Animals are the most physically

diverse kingdom of organisms.• They range in size from twice the

length of a school bus to microscopic

4 Major Characteristics of Animals• 1. They are multi-cellular heterotrophs• 2. Animal cells are supported by collagen

– three-strandedprotein

– found in bone,skin, ligaments,fingernails,and hair

• 3. Animals are diploid and reproduce sexually

Diploid cells have two copies of each chromosome: one copy from the mother and one from the father

• 4. Animals have Hox genes– Homeotic genes control early development.– Hox genes determine the position of cells

differentiation.– A Hox gene mutation leads to the development of

a body structure in the wrong position and/or animal diversity

Animal Diversity• Animals are grouped into vertebrates (animal

with backbones) or invertebrates (animals without backbones)

• More than 95% of all animal species are invertebrates- an animal without a backbone

Animals are grouped according to these 3 criteria

• 1. Body Plan• 2. Tissue Layers• 3. Developmental Patterns

blood vessels

brain

hearts

muscle

segmentnerve cord

mouth

digestive track

gastrovascular cavity

mouth

mesoglea

oral arms

tentacles

There are two types of Body Plans

Bilateral Symmetry Body divides equally along one

plane

Radial Symmetry• Body arranged in a circle

around a central axis

Tissue LayersBilateral

• Have 3 distinct layers: ectoderm, endoderm, and mesoderm– Ecto- develops into skin,

the brain, and nervous system

– Endo- lines the “gut”– Meso- develops into

internal organs

Radial

• Have two distinct layers: ectoderm and endoderm

Animals are separated into two major groups

• Protostome- mouth develops before anus

• Deuterostome- anus develops before mouth

Invertebrate Diversity

Sponges

• Sponges are the most primitive animals on Earth.

• Sponges share common characteristics.– Sessile- attached to floor

of ocean (do not move)– reproduce both sexually

and asexually – filter feeders- strain food

particles from water

Sponges have three types of cells1. Pinacocytes- form

the sponges outer layer

2. Choanocytes- pull water into sponge and help trap food

3. Ameobocytes- absorb and digest food particles

osculum

choanocyte

amoebocyte

pinacocyte

pore

spicule

Sponge Video

Cnidarians (Jellyfish)• Cnidarians come in two body forms

– Polyp- cylindrical tubes with mouth and tentacles facing upward

– Medusa- umbrella-shaped, with mouth and tentacles on the underside

Cnidarian Video

Cnidarian Anatomy• Cnidarians are made up of two tissue layers

separated by mesoglea• The outer tissue layer has three cell types.

– contracting cells – covers the surface of the cnidarian

– nerve cells- sends information around animal to coordinate movement

– cnidocytes (which contain nematocysts)- “stinging cells” used for defense and capturing of prey

barbscoiled nematocyst

dischargednematocyst

Flatworms• Flatworms have a solid body and incomplete

or absent gut. • They have no circulatory system

head

pharynx

mouth

sucker

eyespotreproductivesystem

gut cavity

3 classes of Flatworms

• Planarians- free-living non parasites• Flukes – parasites which can infect humans and cause

serious disease (schistosomiasis) – Infects 200 million people in Africa and Southeast Asia– Contracted by wading in or drinking contaminated

water• Tapeworms- are parasites that live in vertebrates gut

– Use suckers or hooks to attach to host– Absorb nutrients from the food the host eats

Tapeworm Video

Mollusks

• Mollusks have a complete digestive tract with two openings – a mouth and an anus

• Coelom ( fluid filled body cavity)is present– Except in flatworms

• Mollusks have all three tissue layers• Have a brain and spinal cord (cephalization)• Have a circulatory system

– Primitive species (open) such as bivalves– Advanced species (closed) such as octopus and squid

Mollusks Anatomy

• Mollusks share at least one of three features. – radula : file like teeth used to obtain food– mantle : area of tissue covering the internal

organs, sometime secrete a hard outer shell for protection

– ctenidia: flat gills found in the mantle

intestine

stomach

digestive gland

footanus

salivary glandcrop mouth

radula

mantle

mantle cavityheart

• Most mollusks are classified into three classes. – Gastropods: includes snails, abalone, and slugs

they are found on both land and water

– Bivalves (Pelecypods): clams, oysters, mussels, and scallops. Protected by two hinged shells

– Cephalopods: squid, octopus, nautiluses, and cuttlefish. Most advanced mollusks

and are predators

Mollusk Video #1

Mollusk Video

• http://my.hrw.com/content/hmof/science/high_school_sci/tx/gr9-12/hmd_bio_9780544073890_/dlo/biologyvideoclips/index.html?vid=92

Annelids• Three groups of Annelids

– earthworms, leeches, and marine worms• They are characterized by having

segmentation: division of the organism into repeated sections

• They have a coelom and all three tissue layers• They breathe by diffusing oxygen through

their skin• They are hermaphroditic so they can

reproduce either sexually or asexually

Annelid Video

• http://my.hrw.com/content/hmof/science/high_school_sci/tx/gr9-12/hmd_bio_9780544073890_/dlo/biologyvideoclips/index.html?vid=91

Roundworms• Roundworms have bilateral

symmetry and shed their outer skeleton to grow.

• Roundworms are protostomes with bilateral symmetry

brain

cuticle

pharynx intestine

anus

tail

• Roundworms have a psuedocoelom (“false” not complete body cavity)

• They do not have a respiratory or circulatory system