1. Group 3

2. Background

3. Question. Discuss the morphological and functional advances of Deuterostomata in comparison to Protostomata.

4. Key words  morphological –  Functional advances –  Deuterostomata –  Protostomata -

5. Definitions - Protostomes  Protos – first, stomia – mouth  They are characterized by spiral and determinate cleavage, schizocoelous formation of the coelom, and development of the mouth from the blastopore.  The embryonic development of the coalomates starts as a hollow ball of cells called a blastula  This then indent to form a two layer thick ball with a blastopore opening to the outside  In this group, the mouth develops from or near the blastopore  An animal whose mouth develops in this way is called a protostome  If such an animal has a distinct anus or anal pore, it develops later in another region of the embryo

6. Protostomes cont.  The fact that this characteristic development pattern is so widespread in diverse phyla suggest that it was the original pattern for animals as a whole  It also suggests that it was characteristic of the common ancestor of all eumetazoans

7. Deuterostomes  Deuteros – second, stoma – mouth  consist of echinoderms, xenoturbellida, hemichordates and chordates  They are characterised by radial and indeterminate cleavage, enterocoelous formation of the coelom, and development of the anus from the blastopore.  The blastopore gives rise to the anus and the mouth develops from a second pore that occurs in the blastula in later stages of development  Deuterostomes represent a revolution in embryonic growth and development, in addition to the pattern of the blastopore formation there are a number of other embryonic feature differences

8. a) cleavage  The progressive division of cells during embryonic growth is called cleavage  The cleavage pattern relative to the embryo’s polar axis determines how the cells will array.  In nearly all protostomes, each new cell buds off at an angle oblique to the polar axis  As a result, new cell wrestles into the space between the older ones in a closely packed array  this is called spiral cleavage because a line drawn through a sequence of dividing cells spirals outward from the polar axis  In deuterostomes, the cells divide parallel to and at right angles to the polar axis

9. Cleavage cont.  As a result, the pairs of cells from each division are positioned directly above and below one another  This process gives rise to a loosely packed array of cells and is called radial cleavage because a line drawn through the sequence of dividing cells describes a radius outward from the polar axis

10. Coelom formation  As the archenteron develops in a protostome, initially solid masses of mesoderm split to form the coelom ( schizocoelus )  In deuterostomes, the coelom rises as a pair of mesodermal pouches from the wall of the primitive gut  The pouches enlarge until they meet and fuse forming an enterocoelom ( enterocoelous )

12. Nervous system  Nervous system in the deuterostomes is more advanced  The central system has a dorsal tubular nerve chord which is contained in a fluid-filled canal e.g. Branchiostoma  The brain is well developed in deuterostomes e.g. in vertebrates except in Echinoderms which have a central nervous system that gives off radial nerves in each in arm e.g. sea star  This allows extreme coordination of body organs, muscles and development of senses e.g. sight

13. Nervous system cont.  However, Protostomes have rather simple nervous systems with the exception of some annelids and arthropods. Molluscs e.g. octopi have a well developed brain but other animals in the protostome group have ganglia connected by nerve chords.

14. Excretion  Protostomes excrete through simple cells e.g. tubules/canals e.g. in locusts or through nephridia e.g. in earthworms  The Malpighian tubules of insects, arachnids and some other arthropods move solutes and nitrogenous wastes from the body’s fluid  Unlike protostomes, deuterostomes have more complicated excretory systems, with the exception of Echinoderms which lack waste disposal organs, and were waste diffuses from respiratory surfaces. E.g. in starfish, waste is removed by tube feet and papulae through diffusion.  The other deuterostomes have kidneys and these have made this group more successful than the protostomes e.g. in lizards (phylum Chordata)

15. Skeletal system  An endoskeleton is an internal support structure of an animal derived from the mesoderm and is made up of calcium carbonate  The presence of calcium carbonate strengthens the bones  During embryonic development, it is composed of the notochord and the cartilage  The endoskeleton may function for support, protection and serves as an attachment site for muscle thereby providing a means of movement  Endoskeleton is chiefly found in the deuterostomes e.g. lizard and it allows organism to freely grow  An exoskeleton ( a hard outer covering) e.g. a shell in snails provides structural support and help protect the animal.

16. Skeletal syst cont.  In insects e.g. beetles, the chitinous exoskeleton acts as a waterproof i.e. prevents water loss  The annelids and nematodes have a hydrostatic skeleton and the fluid allows organism to change shape and to produce movement

17. Digestive system  In the protostomes, there exist a complete digestive system i.e. a mouth, stomach and anus  The process is less efficient in the protostomes compared to the deuterostomes  In locusts and other arthropods, food is cut up by mouth parts stored in the crop and passed on to the stomach before being digested and waste excreted through the anus  However, deuterostomes have more efficient digestive system except echinoderms which simply secrete digestive enzyme onto their prey and thereafter absorb the nutrients and some have one opening that is used as both the mouth and the anus

18. Circulatory system  All deuterostomes have a closed circulatory system except echinoderms meaning that their blood circulates from aorta to arteries, capillaries and veins without mixing with intestinal fluids  This prevents blood from being contaminated and subsequently the blood’s components being destroyed by other factors/chemicals in the intestinal fluids  This also ensures efficient transportation of blood to all parts of the body  Most deuterostomes (all chordates) use a heart as a pumping organ for the efficient supply of blood at a higher pressure  Most protostomes have no heart, rather they use dorsal vessels to function as a heartThis marks the efficiency of deuterostomes’ circulatory system as compared to protostomes

19. Respiratory system  Small animals such as earthworms (protostomes) have a dense network of capillaries just below the outer skin  This allows oxygen to diffuse directly into the skin and carbon dioxide to be given off  This type of respiratory system required the animal’s skin to be moist for its efficiency(protostomes)  In deuterostomes, some organisms e.g. fish and other aquatic animals use gills for respiration  How ever, higher order deuterostomes have got specialized respiratory organs e.g.; chordates

20. Segmentation  Segmentation permits flexibility for diverse functional requirements  In other words, segmentation gives room for development of specialized organs  A basic element of a body plan is repeated a number of times  The significance of this trend is that each segment, although similar but can be modified for a specific function, nearly independently of other segments

21. Locomotion  Development of post-anal tail in deuterostomes allows propulsion to occur e.g. in fish  In other vertebrates, the tail is used for balance  In protostomes, segments together with chaetae (eg; in annelids) allow more efficient locomotion  Protostomes use longitudinal and/or circular muscles for movement e.g. earthworms and some use suckers e.g. leeches

22. Group members  Skin Obert Dzvuke Edelyne  Nhari Munashe Zhou Kudzaishe  Mutambudzi Blessing Manyisa Brendon  Jariremombe Rodney Shoniwa Munyaradzi  Nyawo George Makuyana Rutendo  Mari Thelma  Toriro Greater  Kamhanda Vanessa  Rosi Barbra  Zinamo Mascot  Tsamasuo Moreblessing  Zvenyika Tinashe  Maruva Panashe