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Hydrozoa

(Class)

Overview

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A class of cnidarians with two body forms, hydroid (polyp) and medusa, generally occurring as different stages of the life cycle. They include the solitary Hydra and the Portuguese Man o' War.

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

Photos

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Taxonomy

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The Class Hydrozoa is further organized into finer groupings including:

Orders

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Anthoathecata

Anthomedusae or Anthomedusa, the athecate hydroids, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed and spectactular group - it has also been called Gymnoblastea, or, with or without an emended ending "-ae", Anthoathecata, Athecata, Hydromedusa or Stylasterina. There are about 1,200 species worldwide. [more]

Anthoathecatae

Anthomedusae or Anthomedusa, the athecate hydroids, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily discussed and spectactular group - it has also been called Gymnoblastea, or, with or without an emended ending "-ae", Anthoathecata, Athecata, Hydromedusa or Stylasterina. There are about 1,200 species worldwide. [more]

Hydroida

Hydroida is an obsolete cnidarian order which united such animals as hydras, hydromedusae, and many marine attached hydroids. However, the group is paraphyletic and not composed from close relatives. But for the largest part, this group makes up what today is usually considered the subclass Leptolinae (or Hydroidolina) which also includes the colonial jellies of the Siphonophora which were not part of the Hydroida. [more]

Lemniscaterina

[more]

Leptothecata

Leptomedusae or Leptomedusa, commonly called thecate hydroids, are a cnidarian order in the subclass Leptolinae. They were formerly placed at suborder rank in the paraphyletic "Hydroida". Their closest living relatives, according to the modern view, are the Anthomedusae which are similar enough to have always been considered closely related, and the very apomorphic Siphonophora which were placed outside the "Hydroida" Given that there are no firm rules for synonymy for high-ranked taxa, alternate names like Leptothecata, Thecaphora or Thecata, with or without the ending emended to "-ae", are also often used for the Leptomedusae. [more]

Leptothecatae

[more]

Limnomedusae

Limnomedusae is an order of jellyfish in the class Hydrozoa. [more]

Milleporina

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]

Siphonophora

Siphonophorae or Siphonophora, the siphonophores, are an order of the Hydrozoa, a class of marine invertebrates belonging to the phylum Cnidaria. 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. The best known species is the dangerous Portuguese Man o' War (Physalia physalis). With a body length of 40?50 m, another species of siphonophore, Praya dubia, is one of the longest animals in the world. [more]

Spongiomorpha

[more]

Trachylina

Trachylinae (also Trachylina, Trachylinida, etc) are a cnidarian subclass of the Hydrozoa. They are placed at order rank in many older classifications, and limited to contain the Narcomedusae and Trachymedusae. But the , then considered an independent order, and probably also the Limnomedusae which were traditionally placed in the paraphyletic "Hydroida", belong to this group too. It is not entirely clear whether the Limnomedusae and the Trachymedusae as conventionally circumscribed are monophyletic [more]

At least 162 species and subspecies belong to the Order Trachylina.

More info about the Order Trachylina may be found here.

Sources

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Last Revised: August 22, 2014
2014/08/22 05:50:33