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Zoology, lecture 5
Cnidaria-Hydrozoa
| Question | Answer |
|---|---|
| Obelia | A genus in the class hydrozoa. They have a complex multi-stage life cycle. |
| Obelia life cycle | Polyp-colony-specialized polyps produce medusal buds-medusae break off (dioceious) and release gametes that meet to form a free swimming planula that settles as a polyp starting again. (medusa is a short stage) |
| Hydra | A solitary fresh-water genus of hydrozoa with no generation changes. They reproduce through sexual/asexual reproduction. They are hermaphroditic. |
| Symbiosis in hydras (also common in other coelenterates | Mutualistic symbiosis with unicellular algae from the group called zoochlorellae that give up some of their photosynthetic products to the organisms that hold them. |
| What are the benefits of the symbiotic relationship for each (the hydras and the zoochlorella)? | The hydras get organic particles as a food source and the zoochlorella get protection and a constant flow of nutrients necessary for photosynthesis. |
| Gastrozooid | A nutritive polyp of colonial coelenterates with tentacles and a mouth. |
| Gonozooids | Reproductive polyps in the colony of polyps in colonial hydrozoa. |
| Scyphozoa anatomy | They have an oral stalk that branches throughout their umbrella distributing nutrients and removing waste. They have gonads too. |
| Common hydrozoa traits | Most have life cycle stages and are colonial (like obelia). Hydra is an exception being solitary with no life stages. |
| Velum | A trait unique to medusas of hydrozoans--a circular membrane around the cap that helps with propulsion. If they don't have it its a scyphozoa. |
| Milleporina | Fire corals (not actually corals) are hydrazoans with a calcium carbonate skeleton that cover the individuals and the entire colony. They bud new polyps and produce medusas with gonads. |
| Physalia physalis | Portuguese man o war is composed of 4 types of polyps including one type that fills with gas and allows it to float |
| Dactylozooids | Polyps in colonial hydras with stinging cells. |
| Hydrozoan locomotion | The polyps are essentially sessile but can disconnect themselves and grab on somewhere else. The medusal stage can float/swim with the help of muscular filaments. |
| Hydrozoan digestion | They paralyze their prey using their cnidocytes and make use of both exocellular and intracellular digestion. Exo--by enzymes secreted into their gastrovascular cavity. |
| Hydrozoan Respiration | They take in oxygen throughout their whole body surface through diffusion. |
| Hydrozoan Sensory/Nervous | They use sensory organelles and a peripheral nervous system. |
| Reproduction | Most have different life cycle stages (like obelia) some show both asexual and sexual reproduction by the polyp stage (like hydras) |
| Scyphozoa | Class of "true jellies". Most are marine--free swimming mostly in shallow waters. The medusa is the main stage (polyp stage exists but its shorter). No velum. Solitary. Thick mesoglea. |
| Scyphozoan size | They can be as many as 2 meters in diameter with tentacles of as much as 40 meters in length. |
| Aurelia | Genus of scyphozoa distinguished by its transparent bell. They eat small animals that swim in the water. |
| Radial canal | Canal of the gastrovascular system in cnidarians. |
| Ring canal | Canal around the periphery of the scyphozoan dome--part of the gastrovascular system. |
| Rhopallium | Sensory centers at the edges of the scyphozoan dome. Clearly visible at the end of the tentacles of young medusae. |
| Gastric pouch | Location of gastric enzyme producing cells and primary digestion. Gonads are also located here. |
| Oral arms | Tentacles of the mouth filled with cnidocytes to disable the food before digestion. There are four of them. They collect the food and bring it to the mouth. |
| Gastral filaments | Elongated structures that contain extra cnidocytes to paralyze prey They can be detached and released into the water (especially when the medusa dies). As soon as they touch a live body they fire the poison even if they aren't connected. |
| Scyphozoa life cycle | Typical scyphozoa go through an asexual and a sexual stage of reproduction. They are dieocious and fertilization is internal. |
| Scyphozoa sexual reproduction | Gametes are released into the gastrovascular cavity, sperm travel to the female and fertilize the egg that stays there until it reaches the stage of free swimming planula that settles on the oral side. |
| Scyphistoma | Sessile polyp of the settled planula. It begins to split cross-wise starting asexual reproduction. |
| Strobila | Stack of asexually produced "cup-like" structures. |
| Ephyra | A young medusa released from the top of the strobila stack. |
| Adult medusa | Grown up ephyra that reproduces sexually through release of gametes from the gonads gastrovascular cavity. |
| Manubrium | Oral ring and tentacles in scyphozoa |
| What is the purpose of the medusal stage in scyphozoa? | Distribution of the species to greater distances. |
| Scyphozoa sensory system | Diffused sensory system with sensory centers around the mouth and at the rhopalium (at the edge of the canopy at the end of the radial canals). There are photoreceptors, chemoreceptors, mechanoreceptors and statocysts. |
| Statocysts | Sensory mechanism used for balance. |
| Statolith | A calcified structure located next to a sensory cillium. When the body changes its orientation the cillium touches the statolith indicating orientation. |
| Scyphozoan movement | Rhythmic contractions allow the animals to move in particular directions by forcing water out of their canopies and advancing in a particular direction. Speed increases with water temperature. |
Created by:
YaelNoa
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