Kingdom: Animalia
Phylum: Cnidaria
Class: Hydrozoa (the hydroids)
Obelia (hydroid colony and medusa prepared slides)
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- The polyp form is stationary, with two distinct types of buds
- The hydranth (gastrozooid) buds are feeding buds, with tentacles covered in stinging nematocysts bringing in food
- Food is distributed throughout the polyp from the gastrozooids to the gonozooids through canals in the manubrium that pump food through the stalks
- The gonangium (gonozooid) buds are reproductive buds, which produce the free-swimming medusa
- The medusa swim away throught the aperture when they are matured
- The free-swimming medusa have male and female forms, which are nearly indistinguishable
- The medusa sexually reproduce, forming planula (larvae) that from new polyps
Hydra (whole mount and cross section prepared slides)
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- Generally live in fresh water
- Spend most of their life sessile (stationary) attached to a surface by a glue-like substance secreted from their basal disc
- Breed by asexual budding or sexually by releasing free-swimming gametes
- Carnivorous, feed on small plankton and invertebrates
- Tentacles on the Hydra have specialized nematocysts that can fire bars to help capture prey.
- Some have a mutualistic relationship with an algae; the algae produce food through photosynthesis while the Hydra protects it