Home     
 

Print This Page

 Major Groups | Cnidaria (hydra, jelly fish) | Hydrozoa (hydra, jellyfish) | Hydridae
 

Hydridae

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
    •  

      Hydra sp.

       

      Hydra sp.

      Taxonomic Checklist: Species (Williams 1980)
      Hydra oligoactis Pallas
      Hydra hexactinella
      Chlorohydra viridissima Pallas

      Distribution: all states

      Sensitivity Rating: SIGNAL grade 2

      Functional Feeding Group: predators

       

      Flying Fox Creek, Darwin NT

      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.

       

      Information Sources: Williams 1980, Pennak 1989, ABRS 2004, Gooderham & Tsyrlin 2002
      Key to Genera: Pennak 1989 (USA)
      Key to Species: none