Garland sea fir (Dynamena pumila)
|Researched by||Charlotte Marshall||Refereed by||Admin|
|Other common names||Minute hydroid, Minute garland hydroid, Garland hydroid||Synonyms||-|
A small hydroid rarely exceeding 7 cm in height. Erect stems rise from a branching stolon. Stems occasionally branched. Branched stems reach greater heights than non branched stems with a maximum of ca 7.5 and 3 cm respectively (Cornelius, 1995b). Hydrothecae are small and variable in shape. Gonothecae are large and pear shaped.
Recorded distribution in Britain and IrelandCommon on all rocky coasts of Britain and Ireland.
Global distributionDynamena pumila is recorded from Arctic Norway to the Atlantic coast of France.
HabitatDynamena pumila is an intertidal hydroid found primarily on kelp and fucoid species where it can form dense populations. It can also be found growing on rock.
- Paired hydrothecae that, combined, look like downward pointing arrows.
- Proximal side of hydrothecae partly attached to stem, distal half free and out-turned.
- Hydrothecae aperture has a cusped margin with two approximately equal cusps.
- Horn coloured perisarc.
Dynamena pumila is found on wave sheltered to moderately wave exposed shores down to the shallow sublittoral. The microhabitat that Dynamena pumila occupies relates to the level of wave exposure of the habitat (Cornelius, 1995b). In sheltered habitats, it may be found on the tips of Ascophyllum nodosum fronds. In slightly more wave exposed habitats, the hydroid may be found lower down on the stipes of Fucus vesiculosus and, on wave exposed coasts, between the holdfasts of Fucus serratus (Cornelius, 1995b). Dynamena pumila is tolerant of brackish conditions.
Dynamena pumila may be confused with Amphisbetia operculata or Tridentata distans, both of which also have paired hydrothecae. However, both species are less common than Dynamena pumila. Amphisbetia operculata is a more delicate species with longer cusps, while the stem of Tridentata distans bears several oblique or triangular nodes/joints (Cornelius, 1995b). Dynamena pumila have no free swimming medusae and planula larvae are brooded in an extension of the gonothecae (acrocyst).
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Cornelius, P.F.S., 1995b. North-west European thecate hydroids and their medusae. Part 2. Sertulariidae to Campanulariidae. Shrewsbury: Field Studies Council. [Synopses of the British Fauna no. 50]
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Manx Biological Recording Partnership, 2017. Isle of Man wildlife records from 01/01/2000 to 13/02/2017. Occurrence dataset: https://doi.org/10.15468/mopwow accessed via GBIF.org on 2018-10-01.
Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1995 to 1999. Occurrence dataset: https://doi.org/10.15468/lo2tge accessed via GBIF.org on 2018-10-01.
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OBIS (Ocean Biodiversity Information System), 2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-12-06
Outer Hebrides Biological Recording, 2018. Invertebrates (except insects), Outer Hebrides. Occurrence dataset: https://doi.org/10.15468/hpavud accessed via GBIF.org on 2018-10-01.
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Yorkshire Wildlife Trust, 2018. Yorkshire Wildlife Trust Shoresearch. Occurrence dataset: https://doi.org/10.15468/1nw3ch accessed via GBIF.org on 2018-10-02.
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Last Updated: 07/04/2005