INTRODUCTION TO THE ANIMAL KINGDOM

Common Patterns and Development in Animals

What Are Animals?

• Animals are multicellular• Eukaryotic• Heterotrophic by ingestion (usually)• Four key branch points:

1. Parazoa (No Tissues) vs. Eumetazoa (Tissues)

2. Radiata vs. Bilateria (Body Symmetry)

3. Acoelomate vs. Coelomate (Body Cavity Present)

4. Protostome vs. Deuterostome (Development)

Two Main Body Plans

Early Embryonic Development

Bilateral Body Plans

1. Must have 3 germ cell layers: Ectoderm, mesoderm, and endoderm.

2. Body cavity may be fully-lined, or partially-lined with mesoderm.

Animal Phlogeny Review

Animal Phylogenetic Tree

Phylum Porifera (Parazoa)Animals with porous bodies

Early Choanocyte Organism May Have Preceded Sponges

Sponge Anatomy

Summary of Poriferan Characteristics

No true tissues. Cell layers are loose federations of cells.

Sessile life cycle.

Filter feeders. Water drawn in and filtered by choanocytes (collar cells).

Central cavity called the spongocoel.

Excurrent opening called the osculum.

Contain wandering amoebocytes.

Sexual reproduction. Most are hermaphroditic.

Internal support by spicules: SiO2, CaCO3 or spongin.

Pylum Cnidaria (Stinging-celled Animals)

Body Plan of Cnidarians

Nematocysts Capture Prey

Cnidarian Life Cycle

Free-Living Medusa (Jellyfish)

Summary of Cnidarian Characteristics

Radial symmetry.

Two germ cell layers (Ectodern and endoderm).

Primitive nerve net of cells coordinates movement.

Sessile life style for some forms.

Body cylindrical with tentacles around a mouth.

Gastrovascular cavity for digesting prey.

Sexual reproduction or asexual reproduction by budding.

Nematocysts present: Signature “stinging cells” on tentacles

Phylum Platyhelminthes (Flatworms)

Flatworm Body Plan

Parasitic Flukes

Tapeworm Lifecycle

Phylum Nematoda (Round Worms)

C. elegans

Summary of Nematode Characteristics

The most numerous soil animals with thousands per liter of soil

Dimorphic – Separate male and female forms

Not segmented

Covered by a cuticle.

Complete digestive tract but no circulatory system.

Pseudocoelom partially lined with mesoderm.

Caenorhabitis elegans, DNA fully sequenced and development known cell-by-cell.

Pinworm, hookworm, Trichinella spiralis

Parasitic Nematode Lifecycle

Phylum Annelida (Segmented Worms)

Marin Polychaete Marine Christmas-tree worm

Leech

Earthworm Anatomy

Summary of Annelid Characteristics

Segmented body plan.

Majority are free-living in all environments.

Complete coelom, though segmented by septa.

Earthworms have closed circulatory system and all other systems are well developed.

Hermaphroditic, but only cross-fertilize.

Each segment contains a pair of metanephridia.

Three classes: Earthworms, polychaetes, leeches.

Protostome development.

Phylum Mollusca (Soft-bodied Animals)

Mollusca Are A Diverse Phylum

All Mollusks Have a Similar Body Plan

Clam Body Plan

Summary of Mollusk Characteristics

Bilateral symmetry.

Coelomate

Complete digestive tract, but open cirulatory system.

Many have shells: either single or double (bivalves).

Protostome development.

Possess a mantle and muscular foot.

Phylum Arthropoda (Jointed-leg Animals)

Summary of Arthropod CharacteristicsAll possess an exoskeleton composed of chitin with jointed body and appendages.

Open circulatory system.

Bilateral symmetry with true coelom.

Protostome development.

Some born as immature nymphs (small versions of adults), others born as larvae which undergo metamorphosis to adult form.

May be classified by body segments, number of legs, mouth parts, or development.

Arthropod Body Plan

Insect Body Plan

Arachnid Body Plan

Phylum Echinodermata(Spiny-skinned Animals)

Echinoderm Anatomy

Summary of Echinoderm Characteristics

Radial Symmetry (larval stages may be bilateral) but may have evolved from bilateral ancestors.

True coleom.

Deuterostome development.

Possess a water vascular system with tube feet for locomotion.

All marine.

Phylum Chordata

Summary of Chordate Characteristics

There are five main chordate features. These features are frequently temporary, only appearing during embryonic development.

Notocord present: Dorsal, flexible rod or cartilage functioning as support. Usually replaced by bone in most chordates.

Dorsal hollow nerve cord: Forms basis for nervous system. May become brain and spinal cord.

Pharyngeal gill slits: May become gills, or features of the head.

Muscular tail: Extends beyond the digestive tract. Often lost in development.

Somites present: Muscle segments blocks of mesoderm. Chordates are segmented animals.

Dorsal Nerve Cord Develops From A Fold In The Dorsal Embryonic Ecotoderm

Phylum Chordata - Chordates

Lancelet Anatomy

Tunicate and Tunicate Larva(Primitive Chordate)

LarvaAdult

Classes of Subphylum Vertebrata

Agnatha – Jawless fish: Hagfish, lampreys

Chondrichthyes – Cartilaginous fish: Sharks, rays, skates

Osteichthyes – Bony fish

Amphibia – Salamanders, frogs, toads

Reptilia – Snakes, turtles, crocodilians

Aves – Birds

Mammalia - Mammals

THE END