HYDROZOANS
Hydrozoans are very appealing objects to be investigated by amateurs. Most of them are marine animals. To study those animals you may use a microscope with low magnification (objective 4x) or a stereo microscope, which is much more appropriate. Sessile forms can easily be collected in shallow water, planktic forms are collected using a plankton net with meshes not too small.
The processing of the samples so obtained is quite simple: Fixation with formaldehyde 4%, staining with borax-carmine, dehydration with mixtures of alcohol / water of increasing content of alcohol, treatment with isopropanol, after that treatment with toluene or xylene, then mounting with artificial resin.
A characteristic feature of the reproduction of these animals is a change between a sessile polyp stage and a planktic medusa stage. The polyps bud off small medusae which develop gonads after having reached maturity. After fertilization small larvae develop which settle at solid surfaces and become polyps afterwards.
The reproductive scheme described
varies widely from group to group: The polyps very often form moss-like or branched
colonies (vegetative propagation). The medusa stage may be suppressed and the
gonads develop at highly specialized polyps. In that case the gonads are thought
to be the residue of completely reduced medusae. On the other hand there are
pelagic medusae without any polyp stage. It is this wealth of different shapes
in combination with the adaptation to different habitats which make these easily
obtainable animals so attractive to amateurs.
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Laomedea sp. |
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| Polypenstock
mit unspezialisierten Polypen . |
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Laomedea sp. |
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| Geschlechtspolyp (sog. Gonangium) . |
Medusenstadium ("Obelia") |
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Coryne |
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| Spezialisierter
Polyp . |
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Margelopsis sp. Rathkea sp. |
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Margelopsis
sp. Pelagischer Polyp . |
Margelopsis
sp. Medusenstadium . |
Rathkea
sp. Medusenstadium . |
| Vertillium sp. |  |
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| Polypententakel mit Gonaden . |
Polypententakel mit Gonaden . |
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| Tubularia sp. |  |
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| Polyp . |
Polyp |
Actinulalarve . |
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| Sertularia sp. |  |
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| Kolonie
mit leeren Theken . |
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| Plumellaria sp. |  |
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| Polypen |
Polypen und Gonangium . |
Polypen und Gonangium |
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| Plumellaria sp. |  |
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| Gonangien . |
Gonangien . |
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