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 tissue 2.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 Direction When studying and describing animals, some basic body characteristics are important. These include: Animal Body Symmetry Animal Body Symmetry - the way body parts are arranged around a center point. (Asymmetry, Bilateral Symmetry, Radial Symmetry) Directions on the body Directions on the body - used to describe areas on the body of an animal. (Dorsal, Ventral, Anterior, Posterior) *segmentation = a series of repeating similar units Ex. Phylum Annelidia, Phylum Arthropoda, Phylum Chordata

Asymmetry = no symmetry

Bilateral and Radial Symmetry Cephalization Cephalization = concentration of nerve tissue and sensory organs at the anterior end of a bilateral organism

Dorsal top surface Anterior front end Posterior hind end Ventral bottom surface Directions on an animal body:

Animal Diversity Animalia - Invertebrata = (10 major phyla) - Chordata = (11 th 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 tissue 2. Dorsal nerve cord = hollow tube 3. Pharyngeal pouches = small out pockets of the anterior part of the digestive tract 4. 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

Eleven Major Animal Phyla

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 Development Germ 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

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. O 2 in; CO 2 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