Obelia - wikipedia Obelia This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. ( June 2013 ) Obelia Scientific classification Kingdom : Animalia Phylum : Cnidaria Class : Hydrozoa Order : Leptothecata Family : Campanulariidae Genus : Obelia Peron and Lesueur, 1810 Species Obelia dichotoma Obelia geniculata Obelia longissima Obelia bidentata Obelia is a genus of hydrozoans, which consists mainly of marine and some freshwater animal species and have both the polyp and medusa stages in their life cycle. The genus belongs to the phylum Cnidaria, which are all aquatic and mainly marine organisms that are relatively simple in structure. It is also called sea fur. Contents 1 Habitat 2 Life cycle 3 Structure 4 Notes 5 References 6 External links Habitat Obelia has a worldwide distribution except the high - arctic and Antarctic seas. The medusa stage of Obelia species are common in coastal and offshore plankton around the world. Obelia are usually found no deeper than 200 metres ( 660 ft ) from the water 's surface, growing in intertidal rock pools and at the extreme low water of spring tides. Life cycle The polyp colony reproduces asexually. During this stage of life, Obelia are confined to substrate surfaces. On this mature colony there are individual hydranths called gastrozooids, which can be found expanded or contracted, to aid in the growth of this organism by feeding ; the reproductive polyp gonozooids has medusa buds. Other hydranths are specialized for defense. The main stalky body of the colony is composed of a coenosarc, which is covered by a protective perisarc. The next generation of the life cycle begins when the medusae are released from these gonozooids, producing free swimming only male medusae velum with gonads, a mouth, and tentacles. The physical appearance of the male and female medusae velum, including their gonads, are indistinguishable, and the sex can only be determined by observing the inside of the gonads, which will either contain sperm or eggs. The medusae reproduce sexually, releasing sperm and eggs that fertilize to form a zygote, which later morphs into a blastula, then a ciliated swimming larva called a planula. The planulae live free - swimming for a while but eventually attach themselves to some solid surface, where they begin their reproductive phase of life. Once attached to a substrate, a planula quickly develops into one feeding polyp. As the polyp grows, it begins developing branches of other feeding individuals, thus forming a new generation of polyps by asexual budding. Structure Through its life cycle, Obelia take two forms : polyp and medusa. They are diploblastic, with two true tissue layers -- an epidermis ( ectodermis ) and a gastrodermis ( endodermis ), with a jelly - like mesoglea filling the area between the two true tissue layers. They carry a nerve net with no brain or ganglia. A gastrovascular cavity is present where the digestion starts and later becomes intracellular. They have incomplete digestive tracts where the food enters, is digested, and expelled through the same opening. During the polyp stage, the mouth is situated at the top of the body, surrounded by tentacles, whereas during the medusa stage, the mouth is situated at the distal end of the main body structure. Four gonads lie in this main body structure, or manubrium. When food is taken in through the mouth, it enters the manubrium. The food is then distributed through a canal system, consisting of four radial canals and an outer ring. Defense and the capture of prey are helped by unique stinging cells called cnidocytes that contain nematocysts, which are triggered by the cnidocil. It has a ridge - like structure on the inner margin, called velum. If the velum is present, it is named as craspedote medusa. Notes Jump up ^ P.K. Gupta ( 2007 ). Genetics Classical To Modern. pp. 1 -- 118. Jump up ^ Cornelius, P.F.S., 1990a. European Obelia ( Cnidaria, Hydroida ) : systematics and identification. Journal of Natural History 24 : 535 - 578. Jump up ^ Cornelius, P.F.S., 1995b. North - West European thecate hydroids and their Medusae. Part 2. Synopses of the British Fauna ( New Series ), No 50. References B. Grzimek ; Grzimek 's Animal Life Encyclopedia ( Volume 1 : Lower Animals ) ; Van Nostrand Reinhold Company. D. George ; Marine Life : An Illustrated Encyclopedia of Invertebrates in the Sea ; Wiley - Interscience Publication. E.P Solomon, L.R Berg, and D.W Martin ( editor ) ; Biology ; Thomson Learning Inc ; ISBN 0 - 534 - 39175 - 3 ( 6th edition, hardcover, 2002 ). J. Moore ( editor ) ; An Introduction to the Invertebrates ; Cambridge University Press L. Gilbertson ; Zoology Laboratory Manual ; The McGraw - Hill Companies, Inc ; ISBN 0 - 07 - 237716 - X ( 4th edition, 1999 ). Some taxonomic information also came from National Center for Biotechnology Information ( NCBI ) External links A Hydroid : Obelia Longissima The Double Life of Obelia Taxon identifiers Wd : Q134802 ADW : Obelia EoL : 18217 EPPO : 1OBELG Fauna Europaea : 240596 ITIS : 49514 NCBI : 32569 NZOR : e31a8b48 - c35e - 46f6 - a9a4 - 6c6330f3767c WoRMS : 117034 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Obelia&oldid=831885666 '' Categories : Leptomedusae Cnidarian genera Hidden categories : Articles lacking in - text citations from June 2013 All articles lacking in - text citations Articles with ' species ' microformats Talk Contents About Wikipedia Azərbaycanca Cebuano Deutsch فارسی Français Bahasa Indonesia Nederlands 日本 語 Polski Русский Svenska Українська Winaray 5 more Edit links This page was last edited on 22 March 2018, at 17 : 36. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. 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Question: various types of zooids found in obelia colony
Answer: gastrozooids