medusa dalam siklus hidupnya. Genus ini berada dalam filum Cnidaria, yang semuanya akuatik dan terutama hidup di laut yang strukturnya relatif sederhana. Transcript of Filum Cnidaria (Coelenterata). Nama Anggota: 1. Fadhil Nurrohman (06) 2. Fika Pebianti (07) 3. Lilastika Cattri (13) 4. Hydrozoa adalah kelas dari anggota hewan tak bertulang belakang yang termasuk dalam filum Cnidaria. Sebagian besar hewan Hydrozoa hidup di laut dan.
Most hydrozoan medusae have just four tentacles, although a number of exceptions exist. The hydrocaulus is usually surrounded by a sheath of chitin and proteins called the perisarc. A few genera within this class live in fresh water. Colonial hydrozoans include siphonophore colonies, HydractiniaObeliaand many others.
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In some, defensive polyps are found, armed with large numbers of stinging cells. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria. Mostly these are simple sensory nerve endings, but they also include statocysts and primitive light-sensitive ocelli.
All colonial hydrozoans also include some polyps specialized for reproduction. These lack tentacles and contain numerous buds from which the medusoid stage of the lifecycle is produced. Especially the presumed phylogenetic distinctness of the Siphonophora is a major flaw that was corrected only recently.
Unlike some other cnidarian groups, the lining of the central cavity lacks stinging nematocystswhich are found only on the tentacles and outer surface. The medusae of hydrozoans are smaller than those of typical jellyfish, ranging from 0. Hydroid colonies are usually dioeciouswhich means they have separate sexes—all the polyps in each colony are either male or female, but not usually both sexes in the same colony.
In others, one polyp may develop as a large float, from which the other polyps hang down, allowing the colony to drift in open water instead of being anchored to a solid surface. In addition, there exists a cnidarian parasitePolypodium hydriformewhich lives inside its host’s cells. These tiny, new medusae which are either male or female mature and spawn, releasing gametes freely into the sea in most cases.
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They may have a tree-like or fan-like appearance, depending on species. Historically, the hydrozoans were divided into a number of ordersaccording to their mode of growth and reproduction.
Other such orders were the AnthoathecataeActinulidaeLaingiomedusaePolypodiozoaSiphonophora and Trachylina. Views Read Edit View history. ITIS uses the same system, but unlike here, does not use the oldest available names for many groups. The nervous system is unusually advanced for cnidarians. The colonies are generally small, no more than a few centimeters across, but some in Siphonophorae can reach sizes of several meters.
Hydrozoan systematics are highly complex.
It was traditionally placed in its own classPolypodiozoa, and this view is often seen to reflect the uncertainties surrounding this highly distinct animal. Some examples of hydrozoans are the freshwater jelly Craspedacusta sowerbyifreshwater polyps HydraObeliaPortuguese man o’ war Physalia physalischondrophores Porpitidaekllasifikasi air fern ” Sertularia argenteaand pink-hearted hydroids Tubularia.
As far as can be told from the molecular and morphological data at hand, the Siphonophora for example were just highly specialized “hydroids,” whereas the Limnomedusae —presumed to be a “hydroid” suborder —were simply very primitive hydrozoans and not closely related to the other “hydroids. An additional shelf of tissue lies just inside the rim, narrowing the aperture at the base of the umbrella, and thereby increasing the force of the expelled jet of water.
Partially digested food may then be passed into the hydrocaulus for distribution around the colony and completion of the digestion process.
Where the hydrocaulus runs along the substrate, it form a horizontal root-like stolon that anchors the colony to the bottom. In any given colony, the majority of polyps are specialized for feeding. A tube-like structure hangs down from the centre of the umbrella, and includes the mouth at its tip. In some species, the reproductive polyps, known as gonozooids or “gonotheca” in thecate hydrozoans bud off asexually produced medusae.
Stinging cells are found on the tentacles and around the mouth. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. In addition to these two basic types of polyps, a few colonial species have other specialized forms.