Animals: An Introduction

Characteristics of Animals

All are multicellular All are heterotrophic Most are motile, (can move), at

least some part of life cycle Most undergo a period of

embryonic development during which 2 or 3 layers of tissues form

What is an animal?

- Multicellular- Need water, food, and oxygen to survive- Heterotrophs

* Carnivores (Predators of Prey) (Eat other animals)

* Herbivores (Eat plants)* Omnivores (Eat plants and other animals)

How the first animals might have evolved from unicellular organisms Scientists have inferred that multicellular

invertebrates may have developed from colonies of loosely connected, flagellated protists (b/c protists are heterotrophic and eukaryotic)

The “Backbone” of Animal Classification

95 % Invertebrates (No backbone) - jellyfish, worms, snails, spiders, insects)

5 % Vertebrates (Backbone) – fish, amphibians, reptiles, birds, mammals)

Two kinds of tissue found only in animals:1. Nervous tissue2. Muscle tissue

The Nature of Animals (Kingdom Animalia)

Invertebrates = 95% of all animals Vertebrate an animal with a backbone (5% of animals)

- Vertebrata is a subphylum of the phylum Chordata

- Vertebra one of the repeating bony units of the backbone

Animals are Multicellular- specialization the differentiation of a cell for a

particular function - cell junction connection between cells that

holds them together as a unit Heterotrophy requires ingestion the taking in of

organic matter

The Nature of Animals (Kingdom Animalia) cont… Sexual Reproduction and Development:

- Sexual reproduction = two haploid gametes fuse into a zygote

- zygote the first cell of a new individual in sexual reproduction

Development causes the cells to undergo differentiation

- differentiation a process through which cells become different from one another

Movement is made possible by two tissue types (muscle and nervous tissue)

- Nervous tissue perceives signals from stimuli

- neuron a cell that transmits electrical signals

- muscle tissue receives nerve impulses and responds to the stimuli

Symmetry & Body DirectionSymmetry & Body Direction

When studying and describing animals, some basic body characteristics are important. These include:

Animal Body SymmetryAnimal Body Symmetry - the way body parts are arranged around a center point. (Asymmetry, Bilateral Symmetry, Radial Symmetry)

Directions on the bodyDirections on the body - used to describe areas on the body of an animal. (Dorsal, Ventral, Anterior, Posterior)*segmentation = a series of repeating similar unitsEx. Phylum Annelidia, Phylum Arthropoda, Phylum Chordata

Asymmetry = no Asymmetry = no symmetrysymmetry

Bilateral and Radial SymmetryBilateral and Radial Symmetry

• CephalizationCephalization = concentration of nerve tissue and sensory organs at the anterior end of a bilateral organism

Dorsaltop surface

Anteriorfront end

Posteriorhind end

Ventralbottom surface

Directions on an animal body:Directions on an animal body:

Animal DiversityAnimalia

- Invertebrata = (10 major phyla)

- Chordata = (11th major phylum)

* Vertebrata =

a subphylum

Features found only in chordates At some stage of development, all

chordates have …1. Notochord = firm, flexible, dorsal rod of

tissue2. Dorsal nerve cord = hollow tube3. Pharyngeal pouches = small out pockets

of the anterior part of the digestive tract4. Postanal tail = muscle tissue behind the

posterior opening of the digestive tract

How chordate characteristics change during development Humans: Notochord = backbone Dorsal nerve cord = spinal cord and

brain Post anal tail and pharyngeal pouches

disappear

ElevenMajorAnimalPhyla

Coelomates

Pseudocoelomates

Acoelomates

Fertilization:

Sea Urchin Fertilization (sperm & egg)

Structural features taxonomists use to classify animals Presence of tissue Number of germ layers Presence and type of body cavity Presence of other features such as a

backbone

Animal Tissue DevelopmentGerm tissue layers produce adult organs

Endoderm = develops into gut lining

Mesoderm = develops into muscles and internal body linings

Ectoderm = develops into skin

Fertilization and Development steps through gastrulation: Fertilization : union of egg and sperm

produces a zygote Cleavage process: one divides

repeatedly to form a blastula Blastula = a hollow ball of cells with a

blastocoel as a central cavity Gastulation forms a gastrula

Embryonic Development

• Zygote = a fertilized egg cell. The zygote then begins to divide and eventually forms a hollow sphere of cells. (called a blastula)

• The blastula continues to grow through cell division and an indentation forms into the sphere. (The embryo is now called a gastrula)

Three primary germ layers of a gastrula

1. Archenteron – forms the throat passage, including the gills or lungs, and the gut and its associated organs, such as the liver and pancreas

2. Ectoderm – forms the outer layer of skin, hair, nails, and nervous system

3. Mesoderm – forms the skeleton, muscles, inner layer of skin, circulatory system, & the lining of the body cavity

Two functions of the body cavity in animals

1. Provides a firm base against which muscles can contract

2. Allows the interior of an animal to move somewhat independently of its exterior

3. The body cavity acts as a reservoir and transport medium for substances in the body

Acoelomates:

The flatworm (planarian) is an acoelomate because it does not have a coelom within its mesoderm layer. Its

digesitive cavity is surrounded by the endodermal layer.

Pseudocoelomates:

Roundworms (Nematoda) and rotifers (Rotifera) have a body cavity (coelom) where organs are found and that can serve as a hydrostatic (fluid-filled) skeleton. Their coelom is called a pseudocoelom because it is not completely lined by mesoderm.

Coelomates: with a true coelom

Coelomates: with a true coelom

All complex animals have a true coelom, including the mollusks, annelids, arthropods, echinoderms and chordates. They have a true coelom that is completely lined by the mesoderm layer. The internal organs in a true coelom are more complex, and they are held in place by mesentaries. In other words, the coelom (white) is completely enclosed within the mesoderm layer (blue). Coelomates have more complex internal organs and a muscular gut (intestines) derived from the mesoderm.

Indirect Development

Body Systems Animals have different systems

in their bodies to take care of the different jobs that allow them to live and function.

We will study the diversity of the animal kingdom by learning about each of these systems and how they function from the simplest of animals to the most complex.

Systems & Functions

Skeletal System – provide protection, support, & motion. This will also include muscular systems.

Digestive System - break down the food taken into the body.

Excretory System - As animals perform their various metabolic processes, protein and nucleic acid, both of which contain nitrogen, are broken down

Ammonia – most toxic; excreted by aquatic organisms

Uric acid- Highly concentrated; excreted by reptiles, birds, and insects

Urea- Least toxic; excreted by mammals, amphibians, and some fish

Digestive system – break down the food taken into the body

- sponges digest food with individual cells- Cnidarians digest food in a central

chamber- All other invertebrates and vertebrates

have a gut (or digestive tract) where food is broken down and nutrients are absorbed by specialized cells that line the gut

Respiratory Systems – involve the exchange of gasses into and out of the animal. O2 in; CO2 out.

Circulatory Systems – Distribute food & oxygen throughout the body and collect cellular wastes. The immune system will also be part of this study.

Open or closed circulatory system

Nervous System – Collects information from the environment and coordinates responses to the environment.

Reproductive System – Can function in several ways: binary fission, budding, or sexually.

Patterns of Development

Protostome Development- Spiral Cleavage of cells- Schizocoely formation of mesoderm

Deuterostome Development

- Radial Cleavage of cells- Enterocoely formation of mesoderm

Patterns of Development Protostome ex. Most invertebrates except

Echinoderms Spiral cleavage = cells divide in a spiral

arrangement Schizocoely formation of the mesoderm =

“split body cavity” the mesoderm forms by rapid division of the cells that lie at the boundary of the endoderm and ectoderm

Patterns of Development Deuterostome – Echinoderms and all

chordates Radial cleavage – cell divisions are at

right angles to the axis form one pole of the blastula to the other

Enterocoely – “gut body cavity” the mesoderm forms by rapid division of cells that line the dorsal part of the blastopore

Protostome

Spiral Cleavage

Deuterostome

Radial Cleavage

Schizoceoly Enterocoely