Department of Zoology at ANDC/Zoology Museum/Museum specimens/Cnidaria/Obelia

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{|cellpadding="5" cellspacing="6" style="width:100%;background:#FFFFFF; border-style:solid; border-width:3px; border-color:#0066FF;" Date & Time : 28, August 2024      
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=Classification=

Phylum - Cnidaria

Class - Hydrozoa

Order - Hydroida

Genus - Obelia

=Common Name=

Sea Fur

=Geographical Distribution=

It is found from Arctic region to the Gulf of Mexico and the Pacific coast, and from Southern California to Oregon. =Habitat=

It is colonial, marine, sedentary hydrozoan zoophyte found attached on piles, rocks and sea weeds in shallow water. =Identifying Features=


 * It is a colonial hydroid.


 * The colony consists of basal horizontal portion, the hydrorhiza which is attached with the substratum and number of vertical branches known as hydrocauli arising from hydrorhiza.


 * The colony is trimorphic having three types of zooids, e.g., hydranth, blastostyle and medusa.


 * Hydranth or polyp has a cylindrical body attached to the axis of the hydrocaulus by its proximal end free at its distal end.


 * It is covered by cup-shaped hydrotheca. It is nutritive zooid of colony.


 * The hypostome is surrounded by a number of solid tentacles provided with nematocytes.


 * Blastostyle or reproductive zooid is cup-shaped without mouth and tentacles.


 * It is enclosed by a covering, gonotheca.


 * It gives rise to buds which later become flattened and develope into new medusae.


 * Medusa is bell-shaped with a concave and convex side. It contains marginal tentacles, four radial canals, a ring canal, four gonads born on the radial canals and hanging central manubrium on the concave side.


 * The medusae are free swimming.


 * Life history of Obelia exhibit an alternation of generation, called metagenesis.