PORT PHILLIP BAY

Hydroid

Enlarge image of Hydroid

Enlarge image of Hydroid

Hydroid

Stereotheca elongata (Lamouroux, 1816)

Taxonomy

Cnidaria : Hydrozoa : Conica : Sertulariidae

View scientific description and taxonomy

Scientific Details

Family level detail.
Colonies may be unbranched or branched and always with two rows of hydrothecae on opposite sides of stem, attached to stem and branches by part of their length. Hydrothecae bilaterally symmetrical, usually with a cuspate aperture with a segmented operculum. Gonophores are sporosacs female producing eggs and the male producing sperm, and protected by a gonotheca. The family Sertulariidae includes many genera and species and is known is a world-wide ranging from the tropics to arctic seas. They occur in all habitats from the intertidal zone to the deepest ocean and are very abundant in cool temperate seas southern Australia. Species range from small simple stems with a few hydrothecae to large, complexly branched pinnate colonies with hundreds of hydrothecae.

Genus level detail.
Colony of pinnate, monosiphonic stems, hydrocladia alternate, hydrotheca attached by at least half length to hydrocladium, with at least four sharp marginal cusps, without operculum, gonotheca ovoid.

Species identification.
Hydrorhiza winding over substrate. Colony comprising many long, flexuous, pinnately branched stems. Hydrothecae tubular, sub-alternate on stem and branches, attached by two-thirds of their length, bent outwards, margin with six to eight sharply pointed cusps. Gonotheca borne on branches, large, triangular, flattened, with a small circular terminal aperture with a raised collar flanked by two long spines. Colour: dark brown, older stems often overgrown by pink coralline algae. Up to 8 cm long.

Taxonomy

Phylum:: Cnidaria
Class:: Hydrozoa
Subclass:: Leptothecatae
Order:: Conica
Family:: Sertulariidae
Genus:: Stereotheca
Species:: elongata

General Description

Colony of individual polyps (hydranths) joined by root-like network of tubular stolons at the base. Colony shape is feather-like (pinnate). Colour: dark brown, older stems often overgrown by pink coralline algae. Up to 8 cm long.

Biology

Stems of these hydroids often wash up on beaches. The hydroids grow and are fertile throughout the year. They are the only species in this genus group and are native to southern Australian and New Zealand waters. The species was probably originally collected from Western Australia by the French Baudin expedition in 1802. The type specimens are in the Natural History Museum, Paris, labelled as "Mers Australes ou de la Nouvelle Hollande".

Habitat

On holdfasts of seaweed, especially stems of seagrasses.

Reefs

Seagrass meadows

Distribution guide

Southern Australia.

Species Group

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

Species Code

MoV 3476

Identify

Hydroids

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.

Cite this page as:
Watson, J., 2011, Hydroid, Stereotheca elongata, in Taxonomic Toolkit for marine life of Port Phillip Bay, Museum Victoria, accessed 08 Jun 2025, http://136.154.202.208:8098/species/7140

Text:

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