2. Prepared by :
Alaa Omar Shada Sara Hamdi Alswearki

3. 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.

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

5. 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

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

11. 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

15. 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

16. 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

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

18. 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

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

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

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

24. 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 .

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

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

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

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

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

30. 5. tracheal tubes:
many insects

31. 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

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

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

35. 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 .

36. 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 .

37. Invertebrates group:
Protozoan protists

38. Porifera (sponges)

39. Cnidaria (coelentratrates)

40. Platyhelminthes (flatworms)

41. Nematoda ( round worm )

42. Annelida (segmented worm)

43. Mollusca

44. Arthropoda

45. Echinodermata