Chapter 25 Invertebrates A Summary AP Biology Spring 2011

Chapter 25Chapter 25Invertebrates

A Summary

AP BiologySpring 2011

Animals Groups Numbers

Chordates Vertebrate chordates: mammals, birds, reptiles, amphibians, jawed fishes, jawless fishesInvertebrate chordates: tunicates , lancelets

Vertebrates: 4500, 8600, 7000, 4900, 21000, 84Invertebrates: 2100

Echinoderms Sea stars, sea urchins 6,000

Arthropods Crabs, spiders, insects 1,113,000 (recent estimates of 10’s of millions)

Roundworms Pinworms, hookworms 22,000

Mollusks Snails, slugs, octopuses 100,000

Annelids Leeches, earthworms, polychaetes

12,000

Rotifers Bdelloids 2,000

Flatworms Turbellarians, flukes, tapeworms

20,000

Cnidarians Jellyfish, hydra 10,000

Placozoans Trichoplax adhaerens 1?

Poriferans Sponges 9,000

Animal OriginsAnimal Origins

Animals: multicelled heterotrophs that ingest other organisms or some portion of them

Tissues are arranged into organs and organ systems

Most motile at some stage of their life cycleThey reproduce sexually, and in some cases

asexually, or bothEmbryos develop through a series of stages

Specialized Cells, Tissues, OrgansSpecialized Cells, Tissues, Organs

Variation in Animal Body Plans ◦Organization:◦All animals are multicellular and show an

internal division of labor ◦A key innovation for animals was development

of tissues ◦Tissue development starts in the embryo

Specialized Cells, Tissues, OrgansSpecialized Cells, Tissues, Organs

Cell: the basic unit of all forms of life◦A neuron is a cell

Tissue: group of similar cells that performs a particular function◦Sciatic nerve is a tissue

Organ: group of tissues that work together to perform related functions◦Brain is a organ

Germ LayersGerm Layers

Tissue Development◦Outer ectoderm is the tissue giving rise to the epithelium that lines the body surfaces and forms other organs, and in some species, serves as an external skeleton (ex. Insect cuticle)

◦Endoderm develops into the gut lining and connective tissues serving as the structural material for an internal skeleton

◦Third tissue layer forms between the other two, mesoderm, which is the source of muscles and other organs in all animals more complex than jellyfishes



Diploblastic: animals with only 2 cell layers, their bodies consist of ectoderm and endoderm, and mesoglea (middle glue) holds two layers together ◦Porifera and cnidarians

Triploblastic: having 3 true cell layers ◦Complex animal phyla

Body Symmetry Body Symmetry

Bilateral Symmetry: body is organized along a longitudinal axis with right and left sides that mirror each other◦Most are triploblastic◦Occurs in humans, lobsters

Radial Symmetry: any cut through the central axis of the organism would produce mirror images◦Occurs in jellies

Symmetry Symmetry

Development of HeadDevelopment of Head

Cephalization: concentration of sensory equipment at one end (usually the anterior, or head end) of the organism

Body Plans Body Plans

Coelomates: posses a body cavity filled with fluid, and this space separates an animal’s digestive tract from the outer body wall◦A true coelom forms from tissue derived from

mesoderm ◦Most complex: Annelida, Mollusca, Arthropoda,

Chordata


Pseudocoelomates: are triploblastic animals with a cavity formed from the blastocoel, rather than the mesoderm ◦Nematodes or roundworms

Acoelomates: have no cavities between their alimentary canal and the outer wall of their bodies ◦Flatworms


Coelom: fluid filled body cavity that is completely surrounded by mesoderm tissue◦Represents advance in course of animal

evolution because it provides a space for elaborate organ systems

◦Like digestive tract or cardiovascular system

From the Primitive To the Complex

No symmetry or radial symmetry Bilateral symmetry

No head Head with sensory apparatus

Mesoglea holds two cell layers together

3 cell layers, including mesoderm

Acoelomate Pseudocoelomate or coelomate

No true tissue True tissues, organs, and organ systems

Little specialization Much specialization

Sessile Motile

Characteristics of AnimalsCharacteristics of Animals

Be familiar with 9 common phyla and representative animals of each

For each animal phyla: think in terms of strategies that animals have evolved to adapt to particular environments and notice the trends of development from simple to complex

Porifera: SpongesPorifera: Sponges

No symmetryHave no nerve of muscle tissuesSessile- do not moveFilter nutrients from water drawn into a

central cavity Consist of two cell layers only: ectoderm

and endoderm connected by noncellular mesoglea

Porifera: SpongesPorifera: Sponges

Have specialized cells but no true tissues or organs, each cell carriers out many functions

Evolved from colonial organisms◦If you squeeze a sponge through fine

cheesecloth it will separate into individual cells that will spontaneously reaggregate into a sponge

Reproduce asexually by fragmentationAlso reproduce sexually: hermaphrodites

Cnidarians: Hydra and JellyfishCnidarians: Hydra and Jellyfish

Radial symmetry Body plan is polyp (vase shaped), which

is mostly sessile, or medusa (upside down bowl shaped), which is mostly motile


Life cycle: some go through a planula larva (free swimming) stage then go through two reproductive stages◦Asexually reproducing (polyp)◦Sexually reproducing (medusa)


Two cell layers only: ectoderm and endoderm connected by noncellular mesoglea

Have a gastrovascular cavity where extracellular digestion occurs

Carry out intracellular digestion inside body cells in lysosomes


Have no transport system because every cell is in direct contact with the environment

All members have stinging cells- cnidoctes◦Containing stingers, which are called nematocysts

Ex. Hydra

Platyhelminthes: Flatworms, Platyhelminthes: Flatworms, TapewormsTapeworms

Simplest animals with:◦Bilateral symmetry◦An anterior end and three distinct cel layers

(ectoderm, endoderm, mesoderm)


Digestive cavity has only one opening for both ingestion and egestion so food cannot be processed continuously

Have solid body and no room for true digestive or respiratory systems to circulate food or oxygen

Flatworms have solved this problem in a unique way

They body is so flat and thin that many body cells can exchange nutrients and wastes by diffusion with the environment

Nematodes: Roundworms Nematodes: Roundworms

Unsegmented worms with bilateral symmetry but little sensory apparatus

Many are parasitic ◦Trichinella causes trichinosis, contracted by

eating uncooked pork C. elegans: widely used as an animal

model in studying genes and embryonic development


C. elegans

Annelids: Segmented Worms Annelids: Segmented Worms (earthworms, leeches)(earthworms, leeches)

Bilateral symmetry with little sensory apparatus

Digestive tract is a tube-within-a-tube consisting of crop, gizzard, and intestine

Nephridia for excretion of nitrogen wastes, urea

Closed circulatory system: heart consists of 5 pairs of aortic arches

Annelids: Segmented Worms Annelids: Segmented Worms (earthworms, leeches)(earthworms, leeches)

Blood contains hemoglobin and carries oxygen

Diffusion of oxygen and carbon dioxide through moist skin

Hermaphrodites

Mollusks: Squids, Octopuses, Mollusks: Squids, Octopuses, Slugs, Clams, and Snails Slugs, Clams, and Snails

Have soft body often produced by a hard calcium-containing shell

Open circulatory system with blood-filled spaces called hemocoels or sinuses


Have bilateral symmetry with 3 body zones:◦Head-foot: contains both sensory and motor

organs ◦Visceral mass: contains the organs of

digestion, excretion, and reproduction ◦Mantle: specialized tissue that surrounds the

visceral mass and secretes the shell


Radula: movable, tooth-bearing structure, acts like a tongue

Most have gills and nephridia

Arthropods: Insecta Arthropods: Insecta (grasshopper), Crustacea (shrimp, (grasshopper), Crustacea (shrimp, crab), Arachnida (spider)crab), Arachnida (spider)

Jointed appendagesSegmented into head, thorax, abdomen More sensory apparatus than in annelids

◦Gives them more speed and freedom of movement

Chitinous exoskeleton protects animal and aids in movement

Arthropods: Insecta Arthropods: Insecta (grasshopper), Crustacea (shrimp, (grasshopper), Crustacea (shrimp, crab), Arachnida (spider)crab), Arachnida (spider)

Open circulatory system with a tubular heart and hemocoels, sinuses

Malpighian tubules for removal of nitrogenous wastes, uric acid

Air ducts called trachea bring air from the environment into hemocoels

Echinoderms: Sea Stars (Starfish) Echinoderms: Sea Stars (Starfish) and Sea Urchins and Sea Urchins

Most are sessile or slow moving They have bilateral symmetry as an

embryo but revert to the primitive radial symmetry as an adult

The radial anatomy of the adult is an adaptation to a sedentary lifestyle


Their water vascular system creates hydrostatic support for the tube feet, the locomotive structures

Reproduce by sexual reproduction with external fertilization


Can reproduce by fragmentation and regenerate◦Any piece of a sea star that contains part of the

central nervous canal will form a completely new organism

Have endoskeleton consisting of calcium plates◦Endoskeleton grows with the body◦Exoskeleton does not and must be shed

periodically

Chordates: Tunicates, LanceletsChordates: Tunicates, Lancelets

Two subphyla of invertebrate chordates Simpler versions of vertebrates


Many of 4 anatomical features that characterize chordates appear only during embryonic development◦Notochord: long, flexible rod that appears

during embryonic development between the digestive tube and the dorsal nerve cord

◦Dorsal, hollow nerve cord: formed from a plate of ectoderm that rolls into a hollow tube


◦Pharyngeal clefts: grooves that separate a series of pouches along the sides of the pharynx; in most chordates the clefts develop into slits that allow water to enter and exit he mouth without going through the digestive tract

◦A muscular tail posterior to the anus

Chordates: Fish, Amphibians, Chordates: Fish, Amphibians, Reptiles, Birds, MammalsReptiles, Birds, Mammals

Have a notochord: rod that extends the length of the body and serves as a flexible axis

Have a dorsal, hollow nerve cordThe tail aids in movement and balance Coccyx bone in humans is a vestige of a

tail Vertebrates

Chordates: Fish, Amphibians, Chordates: Fish, Amphibians, Reptiles, Birds, MammalsReptiles, Birds, Mammals

Birds and mammals are hemeotherms ◦Maintain a consistent body temperature◦All other chordates: fish, amphibians, and

reptiles Cold blooded although some reptiles are

endotherms (heat from within) and are able to raise their body temperature

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Chapter 25 Invertebrates A Summary AP Biology Spring 2011