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Zoology, lecture 9
Invertebrates: Platyhelminthes, cont'd 2
| Question | Answer |
|---|---|
| Biological advances made by the turbellaria | They have an organized nervous system concentrated at ganglia. They have simple eyes. They have a protonephridric excretory system. They can reproduce asexually through budding or autotomy and regeneration. |
| Sexual reproduction in turbellaria | Most of them are hermaphroditic with complementary fertilization. They have a penis and sexual cavity called a genital atrium. They lay individual or groups of eggs which are usually covered with a protective layer to prevent drying out. |
| What's the benefit of hermaphroditism? | They are less dependent on the presence of other individuals. It also ensures more members of the next generation (cause each individual has babies). |
| Location of sex organs in the turbellaria | The testis are on the dorsal side, the sperm duct, oviduct and yolk gland are all on the ventral side. |
| Biological variation in turbellaria | Various colors and shapes. Estimated at 3000 species, considered primitive among flatworms. Most are a number of mm long, some reach lengths of up to 60 cm. |
| Dugesia | Also called planaria, a fresh water species of turbellaria. |
| Two classes of parasitic platyhelminthes | Trematoda תוקלע and cestoda םירושרש |
| Examples of parasitic flatworms | Liver fluke דבכ תקלע Bilharzia היצרהליבה תקלע Cestoda םירושרש |
| Bilharzia | A type of parasitic trematoda that lives in the human digestive system causing bloody urine as one symptom. The male is large and holds the female in his body. |
| Adaptations for parasitism | Changes in body structure and life cycle, disappearance of the digestive system and development of the reproductive system, changes in life length, ensuring finding the host, complicated life cycle that requires the host. |
| Parasitism in nature | It is a secondary trait--organisms start as independent and become parasitic through changes. |
| High reproductive potential in parasites | Necessary because they have a complicated life cycle that is dependent upon the presence of other organisms. |
| Schistosomiasas | Aka bilharzia is a disease caused by a genus called schistosoma. |
| Schistosoma life cycle | (Divided into their human/snail stages)- starting with the human, a female attached to a male in the digestive system of humans produces fertilized eggs released in waste. They develop into miracidium (larva) and live for 2 generation in snails. |
| Schistosoma life cycle (cont'd) | The snails release cercaria into the water where they penetrate human skin and travel through the circulatory system to the digestive system. |
| Cercaria | Life cycle stage of schistosoma that penetrates human skin. It grows in snails and is released into water. |
| Miracidium | Larva of schistosoma produced in the human digestive system and released in waste where they infect snails for their next life cycle stage. |
| Taenia saginata | Cestoda species whose life cycle depends on livestock and humans. |
| Taenia saginata life cycle | They live in livestock flesh in protected covers dissolved by human digestive enzymes. They are eaten by humans where they develop into tape worms. They release fertilized eggs in human waste that reinfect livestock. |
| Scolex | The head-part of the parasitic flatworms that holds on to the host body. |
| Proglottids | Continuously refreshed tapeworm segments that grow behind the scolex and contain both male and female reproductive organs. |
| Gravid proglottids | The last proglottids, furthest from the scolex that are filled with fertilized eggs that are released in waste. |
| Tape worm reproductive organs | The individuals start as males and then become females. The new males impregnate the old females. |
| Platyhelminthes classification | All flat worms are protostomic acoelomates. They do have three embryonic germ layers but no coelom. Their body cavity is filled with mesoderm called mesenchyma. |
| Segmented organisms | Both the Annelida and the Arthropoda phyla are segmented organisms. They are also coelomates. They have a true coelom. They are still protostomic. |
| Annelida | תוקורפ םיעלות |
| Arthropoda | םיילגר יקורפ |
| Coelom | A secondary body cavity lined with mesodermal cells. |
| First organisms with a true coelom | Segmented organisms--annelida and arthropoda. |
| Schisocoelom | Development exclusive to protostomes--The mesoderm develops as a solid mass of migrated cells from the gastrula that splits producing the coelomic cavity. |
| Phyla exhibiting segmentation | Annelida, arthropoda, chordata |
| Segmented animal structures | Their bodies are made up of repeating units. |
| Metameric | Segment after segement structure. Throughout evolution the segments fuse and body parts are formed. |
| Primitive state of segments | In each segment we find representations of each type of body system. (Muscles, coelomic cavity, circulatory system, secretion organs, nervous system structures and ganglia) |
| Primary function of the coelomic cavity | It's used as a cavity to hold the reproductive system. |
| Homomeric organisms | Equal segments along the entire length of the body |
| Heteromeric organisms | Different types/sizes of segments along the length of the body. |
| How is the segmented body formed? | It is the result of the sequential development of coelomic sacs one after the next. |
| Segmented body structure | The digestive tract runs from the top to the bottom and it has coelomic sacs on each side for the entire length. At the points where the coelomic sacs meet there is a double wall. |
| Mesentery | The division between the right/left hand coelomic sacs along the body length. |
| Septum | Double divisions between each sequential coelom. |
| Digestive system in segmented animals | The only part that is continuous along the entire length of the body. |
| Blood vessels and nerve cords in segmented animals | They pass continuously through the entire length of the body both from the right and the left through the septa. The nerves are ventral and the blood vessel is dorsal. |
| Nephridia in segmented animals | They pass through each successive septum spilling in the contents of the previous one. |
| Annelida | Phylum of round worms תוקורפ םיעלות (annulus=ring). There are about 12,000 species in 3 main classes: Hirudinea, Oligochaeta and Polychaeta. |
| Polychaeta | תויפיז-בר םיעלות (lots of whiskers) They have a lot of little things sticking out of their bodies. They are mostly marine. |
| Oligochaeta | תויפיז-לד םיעלות (few whiskers) like earthworms. |
| Hirudinea | תוקולע Class of mostly parasitic worms (some, though, are predators). They are external parasites and they get their name from the substance hirudinin (prevents coagulation) that they secrete. |
| Hirudinin | Substance secreted by hirudinea that prevents coagulation in blood. |
| Features of annelida | Triploblastic protostomic schizocoelic bilaterally (or secondary radial) symmetry. Segmented body, developed sensory/nervous system with ganglia (brain + per segment) closed circulatory system, single direction digestion+ nephridium. |
| Single direction digestive system | Present starting in segmented annelida--they have an oral and anal opening. Food goes in one hole and waste comes out another. |
| Closed circulatory system | They have a number of hearts operating with branches of tubes throughout the entire body. They have no single main heart. |
| Peritoneum | Mesodermal covering of blood vessels and digestive system that surrounds the coelomic cavity. |
| Parapodia | Muscular protrusions from the body wall. They are not limbs. Present only in polychaeta. They can be used for locomotion (swimming) but they are also for increase in surface area (so they function like gills). |
| Secondary radial symmetry in annelida | It is present in sessile species and develops after the bilateral symmetry develops making it secondary. |
| קפצ םורק | Peritoneum--mesodermal lining that covers the coelomic cavity. |
| Cuticle | Thin polysaccharide and protein secretion of the ectoderm (hypodermis) that protects the animal. |
| Annelida musculature | They have round muscles (around them) and longitudinal muscles (down their length). |
| Benefits of the segmentation and metameric division of the coelom. | Offers a place for collecting gametes, the liquid gives hydrostatic pressure (whose support is necessary for muscle function) |
| Segmentation and mechanisms of locomotion | The segmentation offered control of muscles according so segment. Contraction on alternating sides of sequential segments gives snake-like locomotion. Dependent upon the hydrostatic pressure provided by the coelom. |
| Coelomic sacs and digestive system | The coelomic sacs and the liquid inside them offer protection for the digestive tract. |
| Coelom segmentation and circulation | Through diffusion nutrients can come out of the digestive tract, into the coelomic cavity and be transferred, for example, to the body wall where they can function. (Circulatory in addition to the blood) |
| Circulatory system in Annelida | The blood can bring nutrients and remove waste, the coelomic liquid can, through diffusion, carry components for distribution. |
Created by:
YaelNoa
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