Hydroids are small, mostly colonial animals. Most of these are colonial forms that are either erect and tree-like, or prostrate encrustations on mollusk shell (live or dead), rock, and other hard surfaces. The erect species generally grow no taller than 15 cm. The pelagic medusae are like tiny jellyfish.
Some hydroids have alternating benthic and pelagic generations. Reproduction in the group is varied and complex, with many species having a free-swimming planula larva that spends hours to days in the water column before settling to the bottom
The Class Hydrozoa is a member of the Phylum Cnidaria. Here is the complete "parentage" of Hydrozoa:
- Domain: Eukaryota Whittaker & Margulis,1978 - eukaryotes
The Class Hydrozoa is further organized into finer groupings including:
- Family (105): Abylidae · Acaulidae · Aeginidae · Aequoreidae · Agalmidae · Aglaopheniidae · Apolemidae · Apolemiidae · Armorhydridae · Athorybiidae · Australomedusidae · Bonneviellidae · Bougainvilliidae · Calycellidae · Calycopsidae · Campanulariidae · Campanulinidae · Candelabridae · Cladocorynidae · Cladonematidae · Clathrozonidae · Clausophyidae · Clavidae · Codonidae · Corymorphidae · Corynidae · Cuninidae · Cytaeidae · Cytaeididae · Diphyidae · Dipleurosomatidae · Eirenidae · Eleutheriidae · Eucopidae · Eudendriidae · Euphysidae · Eutimidae · Forskaliidae · Geryoniidae · Halammohydridae · Haleciidae · Halicreatidae · Halocordylidae · Halopterididae · Hebellidae · Heterastrididae · Hippopodiidae · Hydractiniidae · Hydridae · Hydrocorynidae · Kirchenpaueriidae · Lafoeidae · Laingiidae · Laodiceidae · Laodieidae · Lemniscateridae · Limnocnididae · Lovenellidae · Malagazziidae · Margelopsidae · Melicertidae · Milleporidae · Mitrocomidae · Moerisiidae · Monobrachiidae · Myriothelidae · Oceanidae · Olindiasidae · Olindiidae · Otohydridae · Pandeidae · Pennariidae · Petasidae · Phialellidae · Phialuciidae · Physaliidae · Physophoridae · Plumulariidae · Polyorchidae · Polypodiidae · Porpitidae · Prayidae · Proboscidactylidae · Protohydridae · Ptilocodiidae · Ptychogastriidae · Pyrostephidae · Rathkeidae · Rhizophysidae · Rhodaliidae · Rhopalonematidae · Russelliidae · Sertulariidae · Solanderiidae · Solmarisidae · Sphaeronectidae · Spongiomorphidae · Stylasteridae · Syntheciidae · Thyroscyphidae · Tiarannidae · Timoididae · Tubulariidae · Velellidae · Zancleidae
- Species: ZipcodeZoo has pages for 2,321 species and subspecies in the Class Hydrozoa.
Abylidae is a family of marine invertebrates in the order Siphonophora. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. [more]
Aeginidae is a family of jellyfish in the order Narcomedusae. Most of the genera include only a single species. [more]
Aequoreidae is a hydrozoan family. There are approximately 30 known species found in temperate and tropical marine coastal environments. Aequoreids include Aequorea victoria, the organism from which the green fluorescent protein gene was isolated. [more]
Bougainvilliidae is a family of marine hydroids in the class Hydrozoa. Members of the family are found worldwide. There are sixteen accepted genera and about ninety three species. [more]
Campanulariidae is a family of animals in the phylum Cnidaria, or stinging celled animals. Campanulariidae is composed entirely of hydroids, a Greek term meaning "Water Animals" applied to the plant-like polyp colonies of the class Hydrozoa. All species of Campanulariidae are aquatic in habitat, primarily inhabiting coastal regions and tidal pools. [more]
Cladonematidae is a small family of anthomedusan hydrozoans. They have stolonal hydroid colonies, and their medusae are benthic and can crawl across the sediment; in many species they have lost the ability to swim however. [more]
Cuninidae is a family of jellyfish in the order Narcomedusae. [more]
Eleutheriidae is a family of anthomedusan hydrozoans. These simple animals have a circular mouth surrounded by a variable number of tentacles, each with adhesive apparatus. The gonads are located in a dorsal brood pouch. [more]
The Haleciidae are a hydrozoan family of the suborder Conica. Their hydroid colonies emerge from a creeping and usually form upright branching colonies; some species' colonies are stolonal though. Their gonophores are typically sporosacs, growing singly or bunched into a glomulus. They remain attached to the hydroids or break off to be passively drifted away; in a few, the gonophores are naked. [more]
The Kirchenpaueriidae are a hydrozoan family of the superfamily Plumularioidea. Their are characteristically set in an alternating fashion as one progresses along the stems, forming two neat rows except in Oswaldella laertesi, which has three such rows. The alternating placement of the hydrocladia can be used to distinguish them from the Plumulariidae which may look superficially similar. [more]
Fire corals are colonial marine organisms that look rather like real coral. However they are technically not corals; they are actually more closely related to jellyfish and other stinging anemones. They are members of the phylum Cnidaria, class Hydrozoa, order Capitata, family Milleporidae. [more]
Oceanidae is one of fifty plus cnidarian families of the order Anthomedusae. It contains nearly fifty species in nine or ten genera. [more]
Olindiidae is a family of jellyfish in the order Limnomedusae. [more]
Pandeidae is a family of hydroids in the class Hydrozoa. Like other jellyfish there is usually a mature medusa form which is pelagic and reproduces sexually and a hydroid or polyp form which is often benthic and reproduces asexually by budding. [more]
Physalia is a genus of the order Siphonophora, colonies of four specialized polyps and medusoids that drift on the surface of the Atlantic, Indian and Pacific oceans. A gas-filled bladder resembling a blue bottle provides buoyancy, and long tentacles of venomous [nematocyst]s provide a means of capturing prey. A sail on the float, which may be left or right-handed, allows the wind to propel Physalia about the sea, often in groups. Individuals sometimes become stranded on beaches, where their toxic nematocysts can remain potent for weeks or months in moist conditions. [more]
The chondrophores or porpitids are a small and very unusual group of hydrozoans today classified as family Porpitidae. Though it derives from an outdated name for this lineage (see below), some still find the term "chondrophore" useful as a synonym to "porpitid" in discussions of the three genera contained therein. [more]
Prayidae is a family of marine invertebrates in the order Siphonophora. They are colonial, but the colonies can superficially resemble jellyfish; although they appear to be a single organism, each specimen is actually a colony of Siphonophora. [more]
Rhopalonematidae are a family of jellyfish in the order Trachymedusae. The family comprises 16 genera and about 35 species. [more]
Solmarisidae is a family of jellyfish in the order Narcomedusae. The name is sometimes spelled "Solmaridae". [more]
At least 34 species and subspecies belong to the Family Zancleidae.
More info about the Family Zancleidae may be found here.
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