Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help
|Researched by||Saskiya Richards||Refereed by||Admin|
|Other common names||-||Synonyms||-|
Obelia dichotoma is generally a colonial hydroid although occasionally is unbranched and solitary. The colonial form varies from being large, erect and loosely fan-shaped or elongate up to 35 cm in height, to being short and either bushy or unbranched up to 5 cm in height. Fan-shaped colonies have stems with alternate first order branches that are almost the same lengths as the stems themselves and give rise to second order branches which, in turn, bear third order branches. The main stems are slender, initially monosiphonic, but thickening with age to become polysiphonic. The stems and branches have a slight zig-zagged appearance, and are marked at the nodes by three to four annulations. The number of annulations at the nodes increases to up 20 towards the base of the colony. The colour of the stems is usually light brown. The medusoid stage of the hydroid consists of a flat, circular, umbrella-shaped bell that has short marginal tentacles and is 0.25 - 0.6 cm wide.
Obelia dichotoma reproduces from mid to late summer by releasing medusae from the gonophores. It has been reported that individual colonies release all of their medusae within a few hours. This species is similar to Obelia bidentata, Obelia longissima and Hartlaubella gelatinosa.
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Last Updated: 13/08/2007