Prepared by : Alaa Omar Shada Sara Hamdi Alswearki

Invertebrates : are animals that do not have a backbone. Most of the animals on earth are invertebrates. Invertebrates are are cold-blooded; their body temperature depends on the temperature of their environment.

Topics will be explained Features of Invertebrates Principles of Invertebrate Taxonomy Systematic position of selected Invertebrate species

A- Body symmetry Features of Invertebrates There are three types of body plan symmetry. 1. Asymmetry :there are no planes of regular symmetry. In protozoans such as rhizopods

2. Radial symmetry: body arranged in circle around a central axis Found in sessile or floating animals. Example : cnidarians and echinoderms

3- Bilateral symmetry: body divides equally along one plane , which splits an animal into mirror-image sides. Animal have dorsal and ventral surfaces , anterior and posterior ends Found in freely mobile animals Includes the majority of invertebrates

B- Cephalization: concentration of sense organs and nerve cells in the front of the organism , associated with the brain and the formation of the head. 1. sponges: no nerve tissue 2. cnidarians: nerve net 3. worms and arthropods: groups of nerves called ganglia 4. mollusks: brain

C- Germ layers : Bilateral animals have three distinct layers of tissue; radial animals have only two. both animal types have ectoderm and endoderm bilateral animals have mesoderm

sponges and cnidarians: two cell layers with a jellylike material between them (diploblastic) other invertebrates have 3 cell layers (triploblastic )

D- Coelom : The main body cavity . According to its presence or absence invertebrates may be classified as : a. Acoelomate: no body cavity, the body volume is filled with mesenchyme and other tissue ,e.g. Platyhelminthes b. Pseudocoelomate: body cavity partially lined with mesoderm , e.g. Nematoda

c. Coelomate: body cavity is fluid filled and it is formed from mesoderm , e.g. Annelida , Mollusca , Arthropoda .

E- Metamerism The arrangement of the organs of the body in series of similar units along the longitudinal axis of the body .

It is most clearly in annelids , the body divided both externally and internally into number of segments( metameres )

F. Cleavage : The mitotic division of the zygote that occurs immediately after fertilization and produces a ball of smaller cells (blastomeres ) Patterns of cleavage : Holoblastic :the whole cell divides ,there being little or no yolk . Meroblastic : part of the egg is involved in the cleavage because of the presence of large amount of yolk .

G- Specialized cells, tissues, and organs: 1. Sponges and Cnidarians: little internal specialization 2. Flatworms: simple organs 3. More complex invertebrates: organ systems

H- Feeding and digestion 1. intracellular digestion: food is broken down inside cells (lower animals)

extracellular digestion: food is digested and then enters the cells – enables digestion of larger pieces of food (higher invertebrates)

H- Respiration diffusion through skin: many worms 2. gills: aquatic invertebrates (many mollusks and arthropods)

3. Mantle cavity: snails 4. Book lungs: spiders

5. tracheal tubes: many insects

I- Circulation 1. open circulatory system: blood does not stay within vessels, empties into sinuses; examples: arthropods, most mollusks 2. closed circulatory system: blood remains within vessels examples: annelids, some mollusks

J- Movement and support 1. hydrostatic skeleton: fluid-filled body cavity supports the muscles; examples: annelids, jellyfish

2. exoskeleton: skeleton is outside the body ;examples: arthropods

Taxonomy (systematics ) :branch of biology concerned with naming and classifying of the diverse forms of life . Binomial System of nomenclature : method of naming plants and animals devised by Carlous Linnaeus . Each species is given a two part name made up of a generic name and specific name .

For example : in the species Musca domestica Musca Is the generic name domestica Is the specific name both generic and specific names are printed in Italics . The generic name has a capital initial letter and the specific name a small letter .

Invertebrates group: Protozoan protists

Porifera (sponges)

Cnidaria (coelentratrates)

Platyhelminthes (flatworms)

Nematoda ( round worm )

Annelida (segmented worm)

Mollusca

Arthropoda

Echinodermata