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Zoology, lecture 7
Invertebrates: Triploblastics, Platyhelminthes
| Question | Answer |
|---|---|
| Triploblastic | Organisms with three embryonic germ layers: Endoderm, Mesoderm, Ectoderm. |
| Acoelomates | Triploblastic organisms with no coelomic cavity (only platyhelminthes) |
| Coelomates | Triploblastic organisms with a coelomic cavity. Among invertebrates its Annelida, Arthropoda, Mollusca and Echinodermata. |
| Coelom | Secondary body cavity (secondary to the gastric cavity) lined with mesodermal cells. |
| Protostomes | The blastopore becomes the organism's mouth, the anus opens elsewhere. Their cellular division in embryonic development is spiral and deterministic. |
| Deuterostomes | The blastopore closes, the mouth opens elsewhere and the anus opens next to the original blastopore opening. Embryonic cellular division is radial, cleavage is indeterminate. |
| Spiral cleavage | (In protostomes) The first two divisions produce 4 equal long cells, the third is closer to the top producing little cells and big cells. |
| Radial cleavage | (In deuterostomes) the first two divsions produce 4 equal long cells, the third is horizontal across the middle producing 8 equal cells etc. |
| Schizocoelom | Coelom formation in protostomes where cells designated mesoderm migrate into the blastocoel where they form coelomic sacs |
| Enterocoelom | Coelom formation in deuterostomes where the endoderm sinks in producing mesodermal pouches that detach forming the coelomic sacs. |
| Coelomic sacs | Secondary body cavity--one on each side of the gastric cavity result from each type of coelomic production. They are lined with mesoderm. |
| Determinate cleavage | Present in protostomes--by the second division of the cells, removal of one cell results in destruction of the embryo. |
| Indeterminate cleavae | Present in deuterostomes--removal of a blastomere does not affect the final product. |
| Acoelomata | Example-platyhelminthes: There is no coelomic cavity, the space between the ectoderm and endoderm is stuffed with mesodermal cells. |
| Pseudocoelomata | Example: Annelida--The coelom is lined on one side with mesoderm and on the inside by endoderm. |
| Coelomata | Example: starting with segmented worms, then everyone. When the two coelomic sacs meet they form a dorsal septum and a ventral septum. The coelom is fully surrounded by mesodermal cells. |
| Which tissues are formed by ectoderm? | Epithelial cells, nerve/sensory cells, cells that line the two openings of the digestive system. |
| Which tissues are formed by mesoderm? | All of the organs and tissues in the body including muscles and reproductive organs. |
| Primary purpose of the coelomic cavity? | It serves as the reproductive cavity. |
| Which tissues are formed by endoderm? | Most of the cells that line the digestive system as well as the glands and organs of the digestive system. |
| Significance of the development of mesoderm | They developed muscles allowing for development of locomotion mechanisms which then required increased sensory development--cephalization. |
| Cephalization | Development of a head/brain where the sensory organs are concentrated and nerve control system is to give the moving animal a direction. |
| Result of an increase in body mass | Surface area:Body volume ration is much higher and now they need a circulatory system to get stuff everywhere. Diffusion distance is too large to be efficient. |
| Bilateral symmetry | Resulted from cephalization which gave the organisms a front and a back. |
| Platyhelminthes | Phylum of flat worms (triploblastic acoelomata). There are three classes Turbellaria are free swimming and Trematoda and Cestoda are parasitic. Most are hermaphroditic. |
| Turbellaria | םיסיר יעלות Free swimming (non parasitic) class of platyhelminthes |
| Trematoda | תוקלע One of the parasitic classes of platyhelminthes |
| Cestoda | םירושרש One of the parasitic classes of platyhelminthes. |
| Bilharzia | A type of flatworm in the class trematoda that causes disease in humans from its parasitic life cycle. |
| Turbellaria characteristics | Relatively ancient class (550 million years old) they live in marine, freshwater and damp land environments. There are about 3000 species making up about 15% of the flat worms. |
| Dugesia | (also called planaria) A species of turbellaria with doro-ventrally flat bodies, a mouth that opens at the rear of the body, an extendable pharynx, they have two simple eye spots. |
| Dugesia locomotion | They have muscle fibers (mesodermal origin) that allow them to move. |
| Turbellaria gastrovascular system | The oral opening leads to the pharynx that widens as it continues splitting into all the parts of the body |
| Turbellaria pharynx structure | It is a muscle that can be extended outwards to catch prey. Part of it is ectodermal. |
| Tricladida | Intestinal pattern in turbellaria with three main branches |
| Polycladida | Intestinal pattern in turbellaria with numerous branching structures throughout the body. |
| Eating patterns of turbellaria | They are mostly predatorial eating small invertebrates they hunt with the help of chemoreceptors. |
| Taxonomic division of the 12 orders of turbellaria | It's based on the structure of the gastrovascular system. |
| Parenchyma | Also called mesenchyma is the spongy mesodermal tissue found between the body wall and the digestive tract in acoelomata. It is filled with internal organs and muscles. |
| Dorso-ventral muscles in turbellaria | Muscles that go from the top to the bottom of the flatworms (there are also peripheral muscles). |
| Musculature in turbellaria | Longitudinal, circular, dorsal/ventral muscles allow for a variety of motion throughout the body. |
| Protonephridia | Organ used for osmoregulation and waste removal in turbellaria and other organisms. |
| Ganglion | A small localized nerve center or brain that controls bodily function. |
| Turbellaria movement | They are very flexible and muscular. They have mucous-secreting glands in their mesoderm that secrete mucous on their surface allowing them to slide along surfaces. They can also push/pull to move. |
| Rhabdites | Column like structures that operate in defense of the organism. |
Created by:
YaelNoa
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