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Species Name: Obelia bidentata
Common Name: Doubletoothed Hydroid
Synonymy: Campanularia spinulosa Bale, 1888
Clytia longitheca Hargitt, 1924
Laomedea bicuspidata Clark, 1875
Laomedea spinulosa Bale, 1888
Obelia bicuspidata Clark, 1875
Obelia biscuspidata Clark, 1875
Obelia corona Torrey, 1904
Obelia longa Stechow, 1921
Obelia multidentata Fraser, 1914
Obelia spinulosa Bale, 1888

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Cnidaria Hydrozoa Hydroida Campanulariidae Obelia

    Please refer to the accompanying glossary for definitions of the descriptive terms used in this report.

    Species Description

    The colonial doubletoothed hydroid, Obelia bidentata, is comprised of erect, slightly zigzag but slender main stems (MarLIN 2012). Lateral branches are typically paired successively on opposite sides of the stem. The minor branches are delicate. A supporting protein-chitinous envelope, called the hydrotheca, surrounds the stem. The hydrotheca is nonliving, elongate and bell-shaped. The minor branches are delicate, pinnate, and curve downward with alternate branchlets that are monosiphonic and bear hydrothecal pedicels at the nodes. The gonotheca is long-abconical with a slightly raised aperture.

    Potentially Misidentified Species

    O. bidentata resembles O. dichotoma, but the former has 10-20 microscopic teeth on the margin of the theca (Ruppert & Fox 1988, MarLIN 2012).


    Habitat & Regional Occurence

    O. bidentata is distributed worldwide in tropical, subtropical and temperate waters (Calder 1991). It is frequently reported from oceanic islands such as Fiji, Hawaii, Seychelles, New Britain, Bermuda, Azores, and the Cape Verde Islands (Millard & Bouillon 1973, Gibbons & Ryland 1989, Cornelius 1992, Medel & Vervoort 2000). The hydroid is found attached to hard substrata such as wood, shells and wrecks, as well as on sandy bottoms (MarLIN 2012). O. bidentata is tolerant of brackish water, and is found from the sublittoral zone down to 200 m.


    Size & Growth

    O. bidentata may exceed 15 cm in height (Ruppert & Fox 1988).


    No information is available at this time


    No information is available at this time


    No information is available at this time


    Calder DR. 1991. Shallow-water hydroids of Bermuda: the Thecatae, exclusive of Plumularioidea. Royal Ontario Mus. Life Sci. Contrib. 154: 1-140.

    Cornelius P. 1992. The Azores hydroid fauna and its origin, with discussion of rafting and medusa suppression. Arquipélago Ciências da Natureza 10: 75-99.

    Gibbons MJ & JS Ryland. 1989. Intertidal and shallow water hydroids from Fiji. I. Athecata to Sertulariidae. Mem. Queensland Mus. 27: 377-432.

    MarLIN. Marine Life Information Network. Marine Biological Association of the UK. Available online Accessed 27 November 2012.

    Medel MD & W Vervoort. 2000. Atlantic Haleciidae and Campanulariidae (Hydrozoa, Cnidaria) collected during the CANCAP and Mauritania-II expeditions of the National Museum of Natural History, Leiden, The Netherlands. Zoologische Verhandelingen 330: 1-68.

    Millard NAH & J Bouillon. 1973. Hydroids from the Seychelles (Coelenterata). Annales du Musée Royal de l’Afrique Centrale, série In-8°, Sciences Zoologiques 206: 1-106.

    Ruppert E & R Fox. 1988. Seashore animals of the Southeast: a guide to common shallow-water invertebrates of the southeastern Atlantic Coast. University of SC Press. Columbia, SC. 429 pp.

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Page last updated: 28 December 2012

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