Hydroidolina | |
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Siphonophorae from Ernst Haeckel's 1904 Kunstformen der Natur | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Cnidaria |
Class: | Hydrozoa |
Subclass: | Hydroidolina Marques & Collins, 2004 |
Orders
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Synonyms | |
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Hydroidolina [1] is a subclass of Hydrozoa and makes up 90% of the class. [2] Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, and Leptothecata. [3]
The phylum Cnidaria contains two clades: Anthozoa and Medusozoa. There are around 3800 species within the clade Medusozoa and it consists of Cubozoans, Scyphozoans, and Hydrozoans. [4]
Hydroidolina are small predatory animals, ranging in 8-30 millimeters in size, [5] exhibiting radial symmetry and are diploblastic (developed from two embryonic layers: ectoderm and endoderm). [4]
The classification below is based on the World Register of Marine Species: [6]
Subclass Hydroidolina
Hydroidolina are commonly found in a variety of marine environments across the world such as deepwater caves or [7] [8] brackish and fresh shallow waters, [9] and can exist as solitary or colonial.[ citation needed ] Benthic polyps can be found on a variety of hard substrates, including both natural and artificial surfaces. Many of them live on other organisms such as fish, tunicates, algae, and crustaceans. Furthermore, they prefer not to settle on sand or similarly textured surfaces unless fauna or flora is present. [10]
Because Hydroidomedusian polyps often settle on other organisms, they are also subject to partake in symbiotic relationships. [11] [12] For example, the bivalve mantle cavity of a mollusk provides a sheltered environment, transporting food due to the current. In exchange, the hydroid protects against intruders. [13]
Hydroidolina are carnivorous suspension feeders.[ citation needed ] Motile medusa use their cnidocytes and tentacles to capture prey.[ citation needed ]
Cnidarians are united by the common characteristic of having a specialized cell called a cnidocyte, which contains an explosive organelle called a cnidocyst, or stinging cell. [1] In Hydrozoans, the cnidocysts are formed from interstitial stem cells in the ectoderm [14] and are used for prey capture and anti-predator defense. [15]
Cnidarians are known to occur in two body forms: the polyp form which is benthic and “stalk-like,” and the medusae form, which is commonly known as the “bell” form. [4]
Polyp forms are sessile as adults, with a single opening (the mouth/anus) to the digestive cavity facing up with tentacles surrounding it. Medusa forms are motile, with the mouth and tentacles hanging down from an umbrella-shaped bell. [4]
Though some outlier Hydrozoans go through a polyploid (polyp) and medusa stage, Hydroidolina, which comprises almost all hydrozoans, goes through an asexual polypoid stage where the polyp fixed to a substrate and a sexual hydroid stage varying from free-swimming medusa to a gonophore that remains attached to the polyp. [4] [16]
An important characteristic of the Hydroidolina is the presence and formation of an exoskeleton. [17] The exoskeleton varies in chemical composition, structural rigidity, thickness, and coverage within the different regions of the colony and protects the coenosarc of the polypoid stage. It originates as epidermal secretions, with the exosarc being produced first by glandular epidermal cells. The exoskeleton can either be bilayered and contain both the exosarc (outer layer) and perisarc (inner layer) or corneous (just perisarc). The exoskeleton contains anchoring structures such as desmocytes and "perisarc extensions." [17]
The Hydroidolina follows a biphasic life cycle, which alternates in occurrence as planula larva, asexual colonial sessile polyps and free-swimming sexual medusa, not all of which may be present in the one life cycle of the Hydroidolina. [4]
Within its benthic phase, polyps of these hydroids attach to soft tissues on organisms, such as the mantle of a mollusk, and reproduce asexually by budding [18] [19] [20]
In the sexual medusa stage, gonophores, which are the reproductive organ that produces gametes, and will stay attached to the polyp as a reduced medusa stage but will sometimes, often rarely, form to become their own medusae. [21]
Other hydrozoan classifications, which are beset by paraphyly however, are still often seen. They do not unite the Leptolinae in a monophyletic taxon and thus do not have any merit according to modern understanding of hydrozoan phylogeny. The alternate name Leptolinae (or Leptolina) was used in older sources for Hydroidolina.
The obsolete name Hydroida was used for a paraphyletic grouping that is now considered synonymous with Hydroidolina but did not include the colonial jellies of the order Siphonophorae.
The complexity of fauna environments in shallow and deep waters is only increased by benthic polyp colonization. These hydroid colonies affect many spatial and temporal settlement patterns of other benthic species due to providing a habitat for a wide variety of organisms, thus promoting species richness and abundance. [22] [23]
These sessile invertebrates could prove to be useful as a measure of environmental changes within their own colonies as well as for changes within near marine environments pertaining to temporal and spatial changes to species distribution and composition, temperature, and food. [24] [25]
Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in fresh water and marine environments, including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are a decentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable flagella used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians are also some of the only animals that can reproduce both sexually and asexually.
Jellyfish, also known as sea jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria.
Hydrozoa is a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in freshwater habitats. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.
Obelia is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyp and medusa stages in their life cycle. Hydrozoa belongs to the phylum Cnidaria, which are aquatic organisms that are relatively simple in structure with a diameter around 1mm. There are currently 120 known species, with more to be discovered. These species are grouped into three broad categories: O. bidentata, O. dichotoma, and O. geniculata. O. longissima was later accepted as a legitimate species, but taxonomy regarding the entire genus is debated over.
Siphonophorae is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 species described thus far.
A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores, which are not related to cnidarians at all. Some groups of Nemerteans also produce larvae that are very similar to the planula, which are called planuliform larva. In a few cnidarian clades, like Aplanulata and the parasitic Myxozoa, the planula larval stage has been lost.
Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. It includes the classes Hydrozoa, Scyphozoa, Staurozoa and Cubozoa, and possibly the parasitic Polypodiozoa. Medusozoans are distinguished by having a medusa stage in their often complex life cycle, a medusa typically being an umbrella-shaped body with stinging tentacles around the edge. With the exception of some Hydrozoa, all are called jellyfish in their free-swimming medusa phase.
Turritopsis dohrnii, also known as the immortal jellyfish, is a species of small, biologically immortal jellyfish found worldwide in temperate to tropic waters. It is one of the few known cases of animals capable of reverting completely to a sexually immature, colonial stage after having reached sexual maturity as a solitary individual. Others include the jellyfish Laodicea undulata and species of the genus Aurelia.
Chrysaora hysoscella, the compass jellyfish, is a common species of jellyfish that inhabits coastal waters in temperate regions of the northeastern Atlantic Ocean, including the North Sea and Mediterranean Sea. In the past it was also recorded in the southeastern Atlantic, including South Africa, but this was caused by confusion with close relatives; C. africana, C. fulgida and an undescribed species tentatively referred to as "C. agulhensis".
Leptothecata, or thecate hydroids, are an order of hydrozoans in the phylum Cnidaria. Their closest living relatives are the athecate hydroids, which are similar enough to have always been considered closely related, and the very apomorphic Siphonophorae, which were placed outside the "Hydroida". Given that there are no firm rules for synonymy for high-ranked taxa, alternative names like Leptomedusa, Thecaphora or Thecata, with or without the ending emended to "-ae", are also often used for Leptothecata.
Haleciidae is a family of hydrozoans. Their hydroid colonies emerge from a creeping hydrorhiza and usually form upright branching colonies, although some species' colonies are stolonal. 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.
A gonophore is a reproductive organ in members of the Hydrozoa which produces gametes. It is a sporosac, a medusa or any intermediate stage. The name is derived from the Greek words γόνος and -φόρος.
Bougainvillia aberrans is a marine invertebrate, a species of hydroid in the suborder Anthomedusae. It was first described by Dale Calder in 1993. They have four radical clusters of marginal tentacles. Bougainvillia aberrans is found in Bermuda in the western North Atlantic Ocean.
Eudendrium ramosum, sometimes known as the tree hydroid, is a marine species of cnidaria, a hydroid (Hydrozoa) in the family Eudendriidae of the order Anthoathecata.
Turritopsis nutricula is a small hydrozoan that once reaching adulthood, can transfer its cells back to childhood. This adaptive trait likely evolved in order to extend the life of the individual. Several different species of the genus Turritopsis were formerly classified as T. nutricula, including the "immortal jellyfish" which is now classified as T. dohrnii.
Pennaria disticha, also known as the Christmas tree hydroid, is a species of athecate hydroid in the family Pennariidae. Colonies are common in the Mediterranean Sea growing on rocks close to the surface. This species has been used in research into prey capture.
Clava is a monotypic genus of hydrozoans in the family Hydractiniidae. It contains only one accepted species, Clava multicornis. Other names synonymous with Clava multicornis include Clava cornea, Clava diffusa, Clava leptostyla, Clava nodosa, Clava parasitica, Clava squamata, Coryne squamata, Hydra multicornis, and Hydra squamata. The larvae form of the species has a well developed nervous system compared to its small size. The adult form is also advanced due to its ability to stay dormant during unfavorable periods.
Zancleidae is a family of cnidarians belonging to the order Anthoathecata.
Rosalindidae is a family of cnidarians belonging to the order Anthoathecata.
Tima nigroannulata, commonly known as the elegant jellyfish, is a recently discovered colonial hydrozoa found on the Pacific coast of Japan.