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Hydrozoa is a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments Sir Richard Owen KCB ( Lancaster, July 20 1804 &ndash December 18 1892) was an English Biologist This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Hydroida is an obsolete Cnidarian order which united such animals as hydras, Hydromedusae, and many marine attached hydroids. Trachymedusae are an order in the Cnidarian class Hydrozoa. They contain some 50 Species, divided among about 30 Genera Trachymedusae are an order in the Cnidarian class Hydrozoa. They contain some 50 Species, divided among about 30 Genera Polypodium is a Monotypic Genus of strange parasitic animals the only genus in family Polypodiidae. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos A class is the Taxonomic rank in the Biological classification of organisms in Biology below phylum and above order. A few genera within this class live in freshwater.
These organisms are related to jellyfish and corals and belong to the phylum Cnidaria. A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments
Some examples of hydrozoans are: Hydra, Obelia, Portuguese Man o' War (Physalia), Chondrophores, air ferns (Sertularia argenta), and Tubularia. Hydra is a Genus of simple fresh-water animals possessing radial symmetry. Obelia is a genus in the class Hydrozoa, which consists of mainly marine and some freshwater Species and have both the Polyp and The Portuguese Man O' War ( Physalia physalis) also known as the blue bubble, blue bottle, man-of-war, or the Portuguese man of war The chondrophores or porpitids are a small and very unusual group of Hydrozoans today classified as family Porpitidae. Air fern or "Neptune plant" is a name given to a product that is in fact composed of a Species of Marine animal called Sertularia argentea, also Tubularian hydroids ( Tubularia spp) appear to be furry pink tufts or balls at the end of long strings thus causing them to be sometimes be called "pink-mouthed"
Hydra, a freshwater genus
The most widely-known and researched freshwater hydrozoan is Hydra, which is found in slow-moving waters. Hydra is a Genus of simple fresh-water animals possessing radial symmetry.
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. A cnidocyte, cnidoblast or nematocyte, is a type of Venomous cell unique to the Phylum Cnidaria ( Corals Hydra eat small crustaceans (such as brine shrimp), insect larvae, and annelid worms. Structure of crustaceans As Arthropods crustaceans have a stiff Exoskeleton, which must be shed to allow the animal to grow ( Ecdysis or molting Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described A larva ( Latin; plural larvae) is a juvenile form of Animal with indirect development, undergoing Metamorphosis (for example The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising Hydra may reproduce sexually, through the spawning of sperm (and thus insemination of eggs on the female body column), or through asexual reproduction (budding). Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization.
Colonial hydrozoans
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). For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked" A planula is the free-swimming flattened ciliated, bilaterally symmetric Larva of a Jellyfish, a Hydrozoan Cnidarian or Colonial hydrozoans include siphonophore colonies, Hydractinia, Obelia, and many others.
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).
External links
- 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
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