Medusozoa

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Medusozoa
Temporal range: Cambrian–Recent
Sea nettles.jpg
Pacific sea nettles, Chrysaora fuscescens
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Subphylum: Medusozoa
Classes [1]

Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. [2] [3] 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. [4] With the exception of some Hydrozoa (and Polypodiozoa), all are called jellyfish in their free-swimming medusa phase. [3] [5]

Contents

Evolution

The phylum Cnidaria is widely accepted as being monophyletic and consisting of two clades, Anthozoa and Medusozoa. Anthozoa includes the classes Hexacorallia, the hard corals, and Octocorallia, the soft corals, as well as Ceriantharia, the tube-dwelling anemones. There is strong support for this group having been the first to branch off from the ancestral line. [6]

Medusozoa includes the classes Staurozoa, Cubozoa, Scyphozoa and Hydrozoa, but the relationships between these are unclear. Analysis using ribosomal RNA subunits suggests that within Medusozoa, Staurozoa was the first group to diverge, with Cubozoa and Scyphozoa forming a clade, a sister group to Hydrozoa. Further study involving the order of mitochondrial genes supports this view, [6] and their possession of linear mitochondrial genomes is striking evidence of the monophyly of medusozoans. [7] The stem group of Medusozoa also includes Auroralumina attenboroughii , the earliest known animal predator from the late Ediacaran. [8] Burgessomedusa from the mid-Cambrian Burgess Shale is the oldest known free-living medusa (commonly known as jellyfish). [9]

The affinities of the class Polypodiozoa, containing the single species Polypodium hydriforme , have long been unclear. This species is an endoparasite of fish eggs and has a peculiar life cycle. It has traditionally been considered to be a cnidarian because of its possession of nematocysts, but molecular studies using 18S rDNA sequences have placed it closer to Myxozoa. Further studies involving 28S rDNA sequences suggest that it is either part of the hydrozoan clade Leptothecata, or a sister taxon to Hydrozoa, and does not group with myxozoans. [10]

Animalia

Ctenophora Comb jelly.jpg

Cnidaria

Anthozoa Actinostola 3.jpg

stem‑group Medusozoa

Estonian Museum of Natural History - Conularia.png

crown‑group Medusozoa

Staurozoa Haliclystus stejnegeri 1.jpg

Hydrozoa Tubularia-indivisa.jpg

Polypodiozoa  ? Polypodium hydriforme C.jpg

Cubozoa Cubozoa.jpg

Scyphozoa Moon jellyfish at Gota Sagher (cropped).JPG

Bilateria Ikaria wariootia (detail).jpg

Characteristics

Medusozoans differ from anthozoans in having a medusa stage in their life cycle. The basic pattern is medusa (usually the adult or sexual phase), planula larva, polyp, medusa. Symmetry is tetramerous, with parts in fours or multiples of four. [11] The mitochondrial DNA molecules are linear rather than circular as in anthozoans and almost all other animals. [12] The cnidae, the explosive cells characteristic of the Cnidaria and used in prey capture and defence, are of a single type, there being nematocysts but no spirocysts or ptychocysts. [4] In contrast, the anthozoan life cycle involves a planula larva which settles and becomes a sessile polyp, which is the adult or sexual phase. [11]

Diversity

There is considerable divergence from the basic life cycle pattern among medusozoans. [11]

Scyphozoa is the group commonly known as "true jellyfish" and occur in tropical, temperate and polar seas worldwide. Scyphozoans generally have planula larvae that develop into sessile polyps. These reproduce asexually, producing similar polyps by budding, and then either transform into medusae, or repeatedly bud medusae from their upper surface in a process known as strobilation. [4]

Cubozoa is a group commonly known as box jellyfish, that occur in tropical and warm temperate seas. They have cube-shaped, transparent medusae and are heavily-armed with venomous nematocysts. Cubozoans have planula larvae, which settle and develop into sessile polyps, which subsequently metamorphose into sexual medusae, [11] the oral end of each polyp changing into a medusa which separates and swims away. [4]

Staurozoa is a small group commonly known as stalked jellyfish. The animals remain attached to the substrate by a stalk at the opposite end from the mouth. Staurozoans can be regarded as large polyps that have partially differentiated into sexually mature medusae. These spawn gametes which develop into non-swimming planulae that crawl away to new locations. [4]

Hydrozoa is a large group of solitary and colonial cnidarians from both marine and freshwater environments worldwide. Hydrozoans exhibit the greatest variety of life cycles among medusozoans, with either the polyp or the medusa stage being missing in some groups. [4] In general, medusae are budded laterally from polyps, become mature and spawn, releasing gametes into the water. The planulae may settle to become polyps or continue living in the water column as medusae. [11]

Related Research Articles

<span class="mw-page-title-main">Cnidaria</span> Aquatic animal phylum having cnydocytes

Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.

<span class="mw-page-title-main">Jellyfish</span> Soft-bodied, aquatic invertebrates

Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle; the medusa is normally the sexual phase, which produces planula larvae that disperse widely and enter a sedentary polyp phase before reaching sexual maturity.

<span class="mw-page-title-main">Scyphozoa</span> Class of marine cnidarians, true jellyfish

The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish.

<span class="mw-page-title-main">Hydrozoa</span> Class of cnidarians

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.

<i>Obelia</i> Genus of hydrozoans

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.

<span class="mw-page-title-main">Rhopalium</span>

Rhopalia are small sensory structures of certain Scyphozoan and Cubozoan species.

A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores. Some groups of Nemerteans also produce larvae that are very similar to the planula, which are called planuliform larva.

<span class="mw-page-title-main">Stauromedusae</span> Order of jellyfishes

Stauromedusae are the stalked jellyfishes. They are the sole living members of the class Staurozoa and belong to the medusozoa subphylum of Cnidaria. They are unique among medusa jellyfish in that they do not have an alternation of polyp and medusa life cycle phases, but are instead interpreted as an attached medusa stage, with a lifestyle more resembling that of polypoid forms. They have a generally trumpet-shaped body, oriented upside-down in comparison with other jellyfish, with the tentacles projecting upwards, and the stalk located in the centre of the umbrella.

<span class="mw-page-title-main">Staurozoa</span> Class of jellyfishes

Staurozoa is a class of Medusozoa, jellyfishes and hydrozoans. It has one extant order: Stauromedusae with a total of 50 known species. A fossil group called Conulariida has been proposed as a second order, although this is highly speculative. The extinct order is largely unknown and described as a possibly cnidarian clade of marine life with shell-like structures, the Conulariida. Staurozoans are small animals that live in marine environments, usually attached to seaweeds, rocks, or gravel. They have a large antitropical distribution, a majority found in boreal or polar, near-shore, and shallow waters. Few staurozoans are found in warmer tropical and subtropical water environments of the Atlantic, Indian, and Pacific Ocean basins, but most are known from the Northern Hemisphere. Over the years the number of discovered species has increased, with an estimated 50 species currently recognized. Information on Staurozoa is sparse, and it is one of the least studied groups within Cnidaria. While often neglected, correctly recognizing the characteristics of this class is crucial for understanding cnidarian evolution.

<i>Phacellophora camtschatica</i> Species of jellyfish

Phacellophora camtschatica, commonly known as the fried egg jellyfish or egg-yolk jellyfish, is a very large jellyfish in the family Phacellophoridae. This species can be easily identified by the yellow coloration in the center of its body which closely resembles an egg yolk, hence how it got its common name. Some individuals can have a bell close to 60 cm (2 ft) in diameter, and most individuals have 16 clusters of up to a few dozen tentacles, each up to 6 m (20 ft) long. A smaller jellyfish, Cotylorhiza tuberculata, typically found in warmer water, particularly in the Mediterranean Sea, is also popularly called a fried egg jellyfish. Also, P. camtschatica is sometimes confused with the Lion's mane jellyfish.

<i>Carybdea</i> Genus of jellyfishes

Carybdea is a genus of venomous box jellyfish within the family Carybdeidae that currently consists of a total of 8 species. This genus of jellyfish are often found in warm waters around the world in waters such as the Mediterranean Sea, the Pacific Ocean, and off the coast of Africa. Their sting can cause a range of effects depending on the species. These invertebrates will go through both sexual and asexual reproduction as they transform from a polyp to medusa. Carybdea have a box-shaped bell with four tentacles and eye-like sensory structures. There are distinct physical markings that differentiate many species within the genus. While Carybdea use their venom to act as predators, they are also preyed on by turtles and various fish. They feed on plankton, invertebrates, fish, and some crustaceans.

<i>Turritopsis dohrnii</i> Species of small, biologically immortal jellyfish

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.

<i>Carukia barnesi</i> Species of jellyfish

Carukia barnesi is an extremely venomous jellyfish found near Australia. Stings can result in Irukandji syndrome, and this species is commonly known as Irukandji jellyfish, although this name does not distinguish it from other Irukandji jellyfish such as Malo kingi.

<span class="mw-page-title-main">Hydroidolina</span> Subclass of hydrozoans

Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. 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.

<i>Crossota norvegica</i> Species of hydrozoan

Crossota norvegica is a species of hydrozoan in the family Rhopalonematidae. It is closely related to Crossota millsae and is found in the Arctic Ocean at depths below 1,000 m (3,300 ft). Crossota norvegica is also known as the deep red jellyfish. This species is described as "alien-like" and is known for its vibrant red hue. It is a small cnidarian, reaching only up to 2 cm in its body size.

Calvadosia cruxmelitensis is a stalked jellyfish which inhabits the intertidal and sublittoral zones of rocky coasts in south-western England and the Atlantic coast of Ireland.

<i>Clytia hemisphaerica</i> Species of hydrozoan

Clytia hemisphaerica is a small hydrozoan-group cnidarian, about 1 cm in diameter, that is found in the Mediterranean Sea and the North-East Atlantic Ocean. Clytia has the free-swimming jellyfish form typical of the Hydrozoa, as well as vegetatively propagating polyps.

<i>Clava multicornis</i> Genus of hydrozoans

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.

<span class="mw-page-title-main">Zancleidae</span> Family of cnidarians

Zancleidae 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.

References

  1. ↑ Subphyla Medusozoa based on "The Taxonomicon – Taxon: Phylum Cnidaria". Universal Taxonomic Services. Archived from the original on 2007-09-29. Retrieved 2007-07-10.
  2. ↑ Marques, Antonio C.; Allen G. Collins (March 2004). "Cladistic analysis of Medusozoa and cnidarian evolution". Invertebrate Biology. 123 (1): 23–42. doi:10.1111/j.1744-7410.2004.tb00139.x.
  3. 1 2 Zapata, Felipe; Goetz, Freya E.; Smith, Stephen A.; et al. (2015). "Phylogenomic Analyses Support Traditional Relationships within Cnidaria". PLOS ONE. 10 (10): e0139068. Bibcode:2015PLoSO..1039068Z. doi: 10.1371/journal.pone.0139068 . PMC   4605497 . PMID   26465609.
  4. 1 2 3 4 5 6 Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 148. ISBN   978-81-315-0104-7.{{cite book}}: CS1 maint: multiple names: authors list (link)
  5. ↑ Kayal, Ehsan; Bentlage, Bastian; Sabrina Pankey, M.; et al. (2018). "Phylogenomics provides a robust topology of the major cnidarian lineages and insights on the origins of key organismal traits". BMC Evolutionary Biology. 18: 68. doi:10.1186/s12862-018-1142-0. PMC   5932825 .
  6. 1 2 J. Wolfgang Wägele; Thomas Bartolomaeus (2014). Deep Metazoan Phylogeny: The Backbone of the Tree of Life: New insights from analyses of molecules, morphology, and theory of data analysis. De Gruyter. p. 67. ISBN   978-3-11-037296-0.
  7. ↑ Bridge, D.; Cunningham, C.W.; Schierwater, B.; et al. (1992). "Class–level relationships in the phylum Cnidaria: evidence from mitochondrial genome structure". Proceedings of the National Academy of Sciences USA. 89 (18): 8750–8753. Bibcode:1992PNAS...89.8750B. doi: 10.1073/pnas.89.18.8750 . PMC   49998 . PMID   1356268.
  8. ↑ Dunn, F. S.; Kenchington, C. G.; Parry, L. A.; Clark, J. W.; Kendall, R. S.; Wilby, P. R. (25 July 2022). "A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK". Nature Ecology & Evolution. doi: 10.1038/s41559-022-01807-x .
  9. ↑ Moon, Justin; Caron, Jean-Bernard; Moysiuk, Joseph (2023-08-09). "A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale". Proceedings of the Royal Society B: Biological Sciences. 290 (2004). doi:10.1098/rspb.2022.2490. ISSN   0962-8452. PMC   10394413 . PMID   37528711.
  10. ↑ Evans, Nathaniel M.; Lindner, Alberto; Raikova, Ekaterina V.; et al. (2008). "Phylogenetic placement of the enigmatic parasite, Polypodium hydriforme, within the Phylum Cnidaria". BMC Evolutionary Biology. 8 (139): 139. doi:10.1186/1471-2148-8-139. PMC   2396633 . PMID   18471296.
  11. 1 2 3 4 5 Collins, A. G. (2002). "Phylogeny of Medusozoa and the evolution of cnidarian life cycles". Evolutionary Biology. 15 (3): 418–432. doi: 10.1046/j.1420-9101.2002.00403.x .
  12. ↑ Kayal, Ehsan; Bentlage, Bastian; Collins, Allen G.; et al. (2012). "Evolution of Linear Mitochondrial Genomes in Medusozoan Cnidarians". Genome Biology and Evolution. 4 (1): 1–12. doi:10.1093/gbe/evr123. PMC   3267393 . PMID   22113796.
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