Major Group: Cnidaria Minor Group: Hydrozoa (Pennak 1989, ABRS 2004) Order: Hydrozoa (Williams 1980) or Hydroida (Pennak 1989, ABRS 2004) Family: Hydridae There is some discrepancy in the literature about the taxonomic level of Hydrozoa. This does not affect the identification of Hydridae. |
Descriptive Features: sessile animals
colour variable, depending on age, type and amount of food ingested
radially symmetrical, main body, “column”, is an elongated cylinder
pedal disc, for substrate attachment, consists of special secretory cells
distal end of column has a circlet of 3 -12 tentacles, typically 5 or 6, length varies from ˝ - 5 X length of column
raised, dome-like hypostome present at end of column in centre of the circlet of tentacles, bears a single opening that is the combined mouth and anus
single, continuous, internal body cavity is a gastrovascular cavity; it continues out into hollow tentacles
nematocysts, minute stinging capsules, imbedded in certain epidermal cells
Total length: 1 - 25 mm
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Hydra sp. |
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Hydra sp. |
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Taxonomic Checklist: Species (Williams 1980) Hydra oligoactis Pallas Hydra hexactinella Chlorohydra viridissima Pallas |
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Distribution: all states
Sensitivity Rating: SIGNAL grade 2
Functional Feeding Group: predators |
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Flying Fox Creek, Darwin NT |
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Ecology: Instream habitat: Hydra are common in freshwater ponds, mountain streams and small lakes. They are found attached to stones, twigs and other submerged plant detritus, often in large aggregations. Feeding ecology: All cnidarians are predators feeding on minute animals such as cladocerans and copepods. They catch their prey with tentacles armed with stinging nematocysts. Habit: Life history: In Hydra, the medusa stage is usually absent. The polyp reproduces both sexually and asexually by budding. |
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Information Sources: Williams 1980, Pennak 1989, ABRS 2004, Gooderham & Tsyrlin 2002 Key to Genera: Pennak 1989 (USA) Key to Species: none |
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