PORT PHILLIP BAY


Hydroid 

Hydrodendron australis (Bale, 1919)

View scientific description and taxonomy

Scientific Details

Family level detail.
Hydroids with a shallow saucer-shaped hydrotheca too small to contain the contracted hydranth. Gonothecae containing sperm and eggs. Colonies range in size from minute single hydrothecae to tall lacey bushes. Many species are cryptic, growing in crevices, while others grow in light on other invertebrates and algae. Depth range of the family is from shallow waters to the deep sea.

Genus level detail.
Colony stolonal or erect, hydrotheca saucer-shaped, hydrotheca shallow dish-shaped with an ancillary protective structure (nematophore) on stem and branches beside the hydrothecae. Gonophores are sporosacs, gonothecae large. Nematophores are small vase-shaped chitinous structures packed with sensitive, readily discharged nematocysts. Their purpose is to protect the permanently exposed hydranth. The population of nematophores on colonies is very variable, some colonies of the same species having many while other colonies have very few, or sometimes none.

Species identification.
Stems branched, polysiphonic, growing from a hydrorhiza loosely attached to substrate. Hydrothecae shallow with a smooth circular margin. Nematophores urn-shaped containing many nematothecae, one on branch beside hydrotheca, sometimes also on the hydrorhiza. Gonotheca large, barrel-shaped, attached to the hydrorhiza, female gonophore containing eggs, the male with sperm. Colour: white to greenish, sometimes with internal patches of black zooxanthallae (microscopic plants) living in the coensosarc. Up to 8 cm long.

Taxonomy

Phylum:
Cnidaria
Class:
Hydrozoa
Subclass:
Leptothecatae
Order:
Conica
Family:
Haleciidae
Genus:
Hydrodendron
Species:
australis

General Description

Colony of individual polyps (hydranths) joined by root-like network of tubular stolons at the base. Colony shape is tree-like or bushy (arborescent). Colour: white to greenish, sometimes with internal patches of black zooxanthallae (microscopic plants) living in the coensosarc. Up to 8 cm long.

Biology

Colonies of this species commence growth in winter and become fertile late spring.

Habitat

On sponges or hanging down in curtains in crevices in clear ocean waters.

Reefs

Distribution guide

Southern Australia.

Species Group

Hydroids

Depth

Shallow (1-30 m)

Water Column

On or near sea floor

Max Size

8 cm

Diet

Plankton or Particles

Harmful

Generally not harmful but still able to sting bare skin.

Commercial Species

No

Identify

Conservation Status

  • DSE Advisory List : Not listed
  • EPBC Act 1999 : Not listed
  • IUCN Red List : Not listed

Author

article author Watson, J.

Jan Watson is a consultant with expertise in hydroid taxonomy.

citation

Cite this page as:
Watson, J., 2011, Hydroid, Hydrodendron australis, in Taxonomic Toolkit for marine life of Port Phillip Bay, Museum Victoria, accessed 30 Jun 2017, http://portphillipmarinelife.net.au:8098/species/7119

Text: creative commons cc by licence