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Zoology, lecture 8
Invertebrates: Platyhelminthes, cont'd
| Question | Answer |
|---|---|
| Coelenterate nervous system | Peripheral nervous system with no concentration of nerves and no centers for coordination. (also called a diffused nervous system.) |
| Platyhelminthes nervous system | Concentration of nerve cells into filaments/strings. They are not spread all over allowing for faster dispersal of information. |
| Ganglions | Local concentrations of nerves (ex. where longitudinal and crossways muscles meet). The more concentrated the nervous system, the more coordination the organism has. |
| Primitive nerve structure | A main nerve ring around the head from which nerve filaments split off down the body. |
| Advanced nerve structure | A cephal ganglion from which two lengthwise strings split off to the sides. |
| Turbelleria nerve centers | Auricle-chemoreceptors, Ocellus-simple eyes, commissures-connective nerves, Cerebral ganglia "brain", Dorsal cord, optic nerve. |
| How did the turbelleria nerve structure change from the primitive ladder to the advanced cord? | The two poles of the ladder got closer until the rungs disappeared resulting in a spinal cord with a pair of ganglia at the end. |
| Turbellaria sensory organs | They have a variety of nerve/sensory cells: mechanoreceptors are concentrated on the ventral side, rhotactic cells, chemosensory cells (at the front), photoreceptors, simple eyes |
| Rhotactic cells | Cells sensitive to the water current. (They allow the worms to go against the current so as not to be forced in with it) |
| Dugesia (planaria) simple eyes | The eye is built of transparent ectoderm (like a lens) that cover pigment cells responsible for blocking the light from certain directions. Photoreceptors on the inside can thereby determine the source and strength of the light source. |
| Turbellaria respiration | They have small thin bodies so they can breath through diffusion through their body wall. (Activity is also a determining factor.) There is no respiratory system. |
| Turbelleria Skeleton/Support system | Their flat bodies are supported by mesenchyma (a cellular parallel to the mesoglea in coelenterates) . They have no skeleton. |
| Turbellaria circulatory system | Their digestive system is gastrovascular and branched. They have no blood. Digestion is intracellular through phagocytosis. |
| Turbellaria excretions and osmoregualtion | Solid waste is released from the mouth. Dissolved waste products (ammonia) are secreted through the body wall after being removed by the protonephridia. |
| Structure of the flame cell system | The flame cells propel water through their tubules where they are filtered. Necessary nutrients diffuse back into the body from the main tube and waste products leave through the nephridiopore. |
| Tubules of the nephridial system | They are covered with a thin epithelial layer thereby allowing for diffusion. |
| Process of urine production | Body liquids/metabolites diffuse into the excretory system, as they pass through the tubules nutrients are reabsorbed while dissolved waste is excreted and osmoregulation is preserved. |
| Ionoregulation | Balance of ion content (also preserved by osmoregulation) |
| Asexual reproduction in Turbellaria | They can reproduce through fragmentation--they break off a part of their body. They can also bud new parts and then split. Their asexual reproduction is based on their regenerative abilities. |
| Autotomy | The act of self-amputation--a method of asexual reproduction found in turbellaria where each piece grows into a whole organism. |
| Other benefits of their regeneration capabilities | Turbellaria can starve for a number of months living off their own tissue (losing up to 2/3 of their body mass) and then regenerate missing parts when conditions improve. |
Created by:
YaelNoa
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