Double-toothed sea fir (Obelia bidentata)
|Researched by||Emily Wilson||Refereed by||Admin|
|Other common names||Double-toothed hydroid||Synonyms||-|
A colonial hydroid comprising erect, slightly zigzag but slender main stems that grow up to about 15 cm. The lateral branches tend to be in pairs, successively on opposite sides of the stem. The minor branches are delicate. The hydrothecae, a supporting, nonliving, protein-chitinous envelope surrounding the stem, is elongate and bell-shaped.
Recorded distribution in Britain and IrelandAround British Isles from the Wash to near Portsmouth.
HabitatFound on inert substrata such as wood, shells, wrecks and on sandy bottoms, sometimes algae. Tolerant of brackish water, sublittoral to at least 200 m, rarely intertidal in pools. Also stranded.
- Colony comprising erect, polysiphonic, slender main stems.
- Lateral branches in pairs, successively on opposite sides of stem.
- Minor branches delicate, with downward curvature in life, pinnate; branchlets alternate, monosiphonic, flexuose, bearing hydrothecal pedicels at nodes.
- Hydrothecae rim with 10-20 cusps, usually bimucronate.
- Gonotheca long-obconical with slightly raised aperture.
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Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.
Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]
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Last Updated: 17/07/2002