Hydrozoa
Scientific classification
Kingdom: Animalia Subkingdom: Metazoa Phylum: Cnidaria Class: Hydrozoa Owen, 1843
Subclasses
Anthomedusae Laingiomedusae Leptomedusae Limnomedusae Siphonophorae Actinulidae Narcomedusae Trachymedusae Polypodiozoa Picture of colonial hydrozoa which I took with a digital camera mounted on a Zeiss stereomicroscope This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... Animalia redirects here. ... Phyla Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented worms Tardigrada - Water bears Onychophora - Velvet worms Arthropoda - Insects, etc. ... Classes Anthozoa - Corals and sea anemones Scyphozoa - Jellyfish Staurozoa - Stalked jellyfish Cubozoa - Sea wasps or box jellyfish Polypodiozoa Hydrozoa - Hydroids, hydra-like animals Cnidaria[1] (IPA: [2]) is a phylum containing some 11,000 species of relatively simple animals found exclusively in aquatic, mostly marine, environments. ... Sir Richard Owen KCB (July 20, 1804–December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ... In biology, a subclass is one level below a class. ... Families See text. ... Binomial name Polypodium hydriforme (Ussov, 1885) Polypodium is a genus of parasitic cnidarians; the only genus in family Polypodiidae. ...

Organisms of the Class Hydrozoa belong to the phylum Cnidaria. Hydrozoans are mostly marine, though a few (Hydra, Craspedacusta) are freshwater. Hydrozoans may be solitary or colonial, and are extremely diverse, both in life-cycle forms and morphology. Most hydrozoan species have both a polyp and medusa stage, but others make use of only one or the other. Like other Cnidarians, Hydrozoans keep form through the use of a hydrostatic exoskeleton. Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... Classes Anthozoa - Corals and sea anemones Scyphozoa - Jellyfish Staurozoa - Stalked jellyfish Cubozoa - Sea wasps or box jellyfish Polypodiozoa Hydrozoa - Hydroids, hydra-like animals Cnidaria[1] (IPA: [2]) is a phylum containing some 11,000 species of relatively simple animals found exclusively in aquatic, mostly marine, environments. ... Animated map exhibiting the worlds oceanic waters. ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ... In zoology, a polyp is one of two forms of individuals found in many species of cnidarians. ... In biology, a medusa (also known as a hydromedusa) is a form of cnidarian in which the body is shortened on its principal axis and broadened, sometimes greatly, in contrast with the hydroid or polyp. ...

Hydrozoa are cnideria which have solid tentacles (as opposed to fluid filled tentacles). They can be divided into two groups, thecates and athecates. The thecates have a solid structure (theca) like a skeleton around the tentacles, into which the tentacles can retreat, the athecates have no such structure which makes them less rigid and more about to move to follow the tides.

The most widely-known and researched freshwater hydrozoan is Hydra, which is found in slow moving waters. Hydra has a pedal disc composed of gland cells that helps it attach to substrates, and like all cnidarians uses nematocysts, or "stinging cells," to disable its prey. Hydra eats small crustaceans (such as brine shrimp), insect larvae, and annelid worms. Hydra may reproduce sexually, through the spawning of sperm (and thus insemination of eggs on the female body column), or through asexual reproduction (budding). Species Hydra americana Hydra attenuata Hydra canadensis Hydra carnea Hydra cauliculata Hydra circumcincta Hydra hymanae Hydra littoralis Hydra magnipapillata Hydra minima Hydra oligactis Hydra oregona Hydra pseudoligactis Hydra rutgerensis Hydra utahensis Hydra viridis Hydra is a genus of simple, fresh-water animals possessing radial symmetry. ... Cnidocytes are prey-capture and defensive cells found on animals of the phylum Cnidaria. ... Classes & Subclasses Branchiopoda Phyllopoda Sarsostraca Remipedia Cephalocarida Maxillopoda Thecostraca Tantulocarida Branchiura Pentastomida Mystacocarida Copepoda Ostracoda Myodocopa Podocopa Malacostraca Phyllocarida Hoplocarida Eumalacostraca The crustaceans (Crustacea) are a large group of arthropods, comprising approximately 52,000 described species [1], and are usually treated as a subphylum [2].They include various familiar animals... Orders See taxonomy Insects (Class Insecta) are a major group of arthropods and the most diverse group of animals on the Earth, with over a million described species—more than all other animal groups combined. ... A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ... Classes and subclasses Class Polychaeta (paraphyletic?) Class Clitellata*    Oligochaeta - earthworms, etc. ... It has been suggested that Parthenogenesis be merged into this article or section. ...

Colonial hydrozoans typically have both a medusa stage and a polyp stage in their lifecycle. They have a base, a stalk, and one or more polyps. Hydrozoan colonies are composed of a number of specialized polyps (or "zooids") - including feeding, reproductive, and protective zooids. Reproductive polyps, known as gonozooids (or "gonotheca" in thecate hydrozoans) bud off sexually-produced medusae. These medusae mature and spawn, producing gametes. Zygotes become free-swimming planula larvae or actinula larvae that either settle on a suitable substrate (in the case of planulae), or swim and develop into another medusae or polyp directly (actinulae). Colonial hydrozoans include siphonophore colonies, Hydractinia, Obelia, and many others. A zygote (Greek: ζυγωτόν) is a cell that is the result of fertilization. ... A planula is the free-swimming, flattened, ciliated, bilaterally symmetrical larva of a hydrozoan cnidarian. ...

The medusa stage is typically the dominant sexually-reproductive phase in hydrozoans that alternate between a polyp and a medusa. The medusa often has a limited lifespan, though, and may die shortly after releasing gametes (as in the case of fire corals).

these arent radial symmetric says jonathan aronson

Some examples of hydrozoans are: Hydra, Obelia, Portuguese Man o' War (Physalia), Chondrophores, air ferns (Sertularia argenta), and Tubularia. Species Hydra americana Hydra attenuata Hydra canadensis Hydra carnea Hydra cauliculata Hydra circumcincta Hydra hymanae Hydra littoralis Hydra magnipapillata Hydra minima Hydra oligactis Hydra oregona Hydra pseudoligactis Hydra rutgerensis Hydra utahensis Hydra viridis Hydra is a genus of simple, fresh-water animals possessing radial symmetry. ... Species Obelia dichotoma Obelia geniculata Obelia longissima Obelia bidentata Hydroids (genus Obelia) are from the class Hydrozoa, which consists of mainly marine and some freshwater species and have both the polyp and medusa stages in their life cycle. ... This article is about the marine invetebrate. ... Genera Porpita Velella Chondrophores are an order of hydrozoans, gelatinous Cnidarians superficially resembling jellyfish. ... Binomial name Sertularia argentea[1] (Linnaeus, 1758) Air ferns (Sertularia argentea) are commonly sold as a curiosity or a decorative indoor plant, and as underwater decorations for aquaria in stores, and are labeled as air ferns. Air ferns do not grow, have any roots, or even have leaves, as they... Binomial name [1] Linnaeus, 1758 Tubularian hydroids () appear to be furry pink tufts or balls at the end of long strings, thus causing them to be sometimes be called pink-mouthed or pink-hearted hydroids. ...

External links

Wikimedia Commons has media related to:

Hydrozoa

• J. Bouillon, M.D. Medel, F. Pagès, J.M. Gili, F. Boero and C. Gravili. 2004. Fauna of the Mediterranean Hydrozoa. Scientia Marina, 68 (Suppl. 2).
• Hydroids from Reunion Island and Indian Ocean
• http://zygote.swarthmore.edu/intro6.html
• Puget Sound Online
• Aquascope
• The Hydrozoa Directory
• Hydrozoa Picture Gallery