Ophioderma longicauda

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Ophioderma longicauda
Smooth brittle star

Smooth brittle star

Systematics
Trunk : Echinoderms (Echinodermata)
Class : Brittle stars (Ophiuroidea)
Order : Ophiacanthida
Family : Ophiodermatidae
Genre : Ophioderma
Type : Ophioderma longicauda
Scientific name
Ophioderma longicauda
( Bruzelius , 1805)

The brown brittle star , also smooth brittle star called ( Ophioderma longicauda ), is one of the largest brittle stars (Ophiuroidea) of the Mediterranean and is one of the echinoderms (Echinodermata). It is the largest nocturnal brittle star.

Systematics

The brown brittle star belongs to the Echinodermata family. Ophioderma longicauda was first described by Bruzelius in 1805 as Asterias longicauda and, due to its obvious resemblance to starfish, it belongs to this class. But despite this superficial resemblance that brittle stars often have with the starfish, which also belong to the asterozoa, they form a class of their own, the Ophiuroidae. Within the Ophiuroidae, the brown brittle star belongs to the order of the Ophiacanthida and to the suborder of the Ophiodermatina. Within this, the genus Ophioderma is assigned to the superfamily Ophiodermatoidea and the family of Ophiodermatidae. The official name of this species is longicauda . O. longicaudum is often mentioned, especially in older literature . It is the same type in masculine notation. However, the International Commission on Zoological Nomenclature assigned the generic name Ophioderma to the female gender, which means that the correct species name must be the feminine version, longicauda . The first description of Ophioderma longicauda is often ascribed to Retzius (1805), although it is a mistake. The title of the publication at that time shows that Retzius presented a thesis that was carried out by Bruzelius. While it was customary at the time to publish a thesis under the name of the doctoral supervisor, today's rules of zoological nomenclature state that the author, in this case Bruzelius, is responsible for the publication (ICZN, 2000, Article 50).

morphology

Ophioderma longicauda can reach a diameter of up to 25 cm. The brown brittle star is thus one of the largest brittle stars in the Mediterranean. It is also the largest known nocturnal brittle star. As with all brittle stars, the shape of its body is radial and flattened towards the main axis. It has a more or less disk-shaped center piece, which appears very small in relation to the five cylindrical , unbranched arms. The disc diameter of O. longicauda can be up to 3 cm, although this size is rarely reached. The arms can be four to five times as long as the disc diameter. In comparison to those of the starfish, they are slender and very mobile and sharply demarcated from the central body disc. They contain the skin skeleton typical of Echinodermata, which is in the form of so-called "vertebrae" that are lined up one behind the other and are articulated with one another. The arms are easily brittle as a result. The skin of the brittle star feels "dry" and coarse due to its granules and small shields. Ophioderma longicauda is mostly brown to black in color with red, white and sometimes olive-green patterns. The pattern varies greatly depending on the location in terms of red or green. The upper, dorsal side is usually darker in color, while the lower, ventral side is usually found lighter with darker patterns, especially on the ventral arm plates and the mouth shields, which are individual plates that regularly appear on the underside between the arm bases. The star-shaped mouth opening is formed by five movable corners of the mouth, which carry immobile skeletal structures. These are the oral papillae on the edge, dental papillae on the median tip and teeth on the mouth of the dental papillae. Like all body orifices of the brittle star, the mouth opening lies ventrally, i.e. on the belly side and is closed by 5 jaw plates. The brown brittle star has no eyes and no anus. Its so-called bursae lie on the sides at the attachment points of the arms. These skin protuberances are used for breathing and are supplied with a constant flow of fresh water at the blink of an eye. Hidden in one of the bursal crevices is a tiny opening through which the internal cavity system communicates with the surrounding seawater. Ophioderma longicauda differs from other species in this genus by having twice the number of bursal fissures, four in each interradial sector. Like all brittle stars, it has no madreporen plates (sieve plates on the body surface, which are actually typical for echinodermata). His feet also have no suction cups, which means that they are not relevant to locomotion, but are used as tactile organs.

distribution and habitat

The brown brittle star is a common component of the Mediterranean macrofauna. It is widespread in the Mediterranean and can also be found in the subtropical and tropical latitudes of the eastern Atlantic . It occurs at a depth between two and 50 meters and is therefore often found near the coast. There he likes to live under stones, which is why you can often find him in the Felslitoral . It feels particularly comfortable in caves and block fields between the stones, but it can also be found on secondary hard floors such as coral bottoms. Young animals in particular can sometimes also be found in seagrass meadows . In general, brown brittle stars prefer to hide under objects such as stones, pieces of coral and the like.

nutrition

Ophioderma longicauda feeds carnivorous on small, slow or fixed ( sessile ) marine animals such as worms, small mussels and plankton as well as on carrion , which it finds on the sea floor. He also does not disdain a detritivore diet, i.e. a diet of all kinds of dead organic matter, such as dead plant material, and even cannibalism has already been observed. By eating detritus and carrion, the brown brittle star helps break down organic material.

behavior

Ophioderma longicauda is nocturnal. He prefers to hide under stones during the day and foraging at night. If this is successful, he uses one of his arms to eat, in order to grab the prey by winding it around the bite and then guiding it under the body disc to the mouth. There the bite is then grasped with the teeth. The prey is digested in the sack-shaped stomach. Since this species, like all brittle stars , does not have an anal opening , the food remains are then spat out again through the mouth opening. In the event of danger, Ophioderma longicauda can shed parts of its arms and regenerate them over time . The regenerated material is noticeable because of its narrower cross-section. Due to its coarseness and spines, its calcareous skin also serves as protection against predators, which are mainly starfish.

Locomotion

In contrast to starfish, brittle stars have no organ processes in their arms. Your arms are mainly used for locomotion. In addition, since their ambulacral feet do not have suction cups , they cannot use them to move. In contrast to its name, the brown brittle star moves less meandering, as do other types of brittle stars, but rather jerkily, by first throwing an arm forward. This is then followed by the two neighboring arms. The tips of the arms are pressed into the ground to lift the disc. This is then pulled forward. Finally, the other two arms are pulled along. Ophioderma longicauda thus reaches a speed of almost two meters per minute. The brown brittle star also climbs in this way by clinging to bumps, using all available support, including other animals. Ophioderma longicauda is very mobile and, in addition to crawling and climbing, can also perform defensive movements and turn itself in a few seconds if it falls on its back.

Reproduction and development

Ophioderma longicauda is separate from the sexes . Eggs or sperm are first emptied into the bursae. The gametes are then released into the sea water, the spawning season of this species taking place in early July. External fertilization occurs when the egg and sperm come together by chance. During fertilization, a freely swimming ( pelagic ) Vitellaria larva develops, which feeds lecithotrophically, i.e. on yolk and does not take in any food from outside. The duration of this pelagic larval stage amounts to six days, after which the larva finally develops through metamorphosis into a fully grown brittle star and passes over to life on the ground.

Cryptic kind

In addition to the above-described reproduction by releasing gametes into the open water, there are also developmental lines of the brown brittle stars, in which the female incubates the eggs in the body and gives birth to live young. The first brooding brown brittle star was discovered in Lebanese waters in 2000. This breeding season takes place in May to early June. The young are for several weeks until the adult stage hatched in the bursae of the mother, unless special force stresses the mother to repel the young. This breeding form of Ophioderma longicauda is found mainly in the eastern Mediterranean, while the non-breeding form is mainly found in the western parts of the Mediterranean. Since fertilization of brooding brown brittle stars takes place before the beginning of May, but the spawning season of non-brooding ones at the beginning of July, both groups are reproductively isolated, which means that they cannot reproduce with one another. Thus, they can be described as cryptic species , with an estimated time of separation of 550,000 years. While individuals of the breeding, cryptic species show a higher temperature resistance and regeneration rate, the free-swimming larval stage of the non-breeders ensures fifty times higher migration rates and the external fertilization in the open water leads to a genetic diversity that is up to twice as high . The two cryptic species cannot be distinguished morphologically. However, there are indications that the coloration tends to be greenish in breeding females, whereas a reddish color predominates in the non-breeding females. Also, brooding individuals are mostly smaller than non-brooding ones. Furthermore, breeding Ophioderma longicauda can usually be found at a depth of one to three meters, while non-breeding individuals are usually found between three and twelve meters. According to the latest molecular findings, Ophioderma longicauda is a species complex made up of three brooding lines of development and three non-brooding lines of development that occur in different regions in the Mediterranean and Atlantic. These lineages are distinguished by their differences in mitochondrial DNA .

Human threat

The brown brittle star is threatened by overfishing , as it is popular as an aquarium animal around the Mediterranean. It is relatively easy to keep in the aquarium because it can be fed with small pieces of meat. Due to its interesting appearance and its ability to tolerate high water temperatures, and above all because it eats detritus and "pests" and is therefore suitable as a "cleaner" for the aquarium, the brown brittle star is often collected, both by private individuals and by industrial for sale. Collecting this species is particularly easy as they live very close to the coast and at shallow depths. Simple snorkeling equipment is sufficient to catch Ophioderma longicauda . Although Ophioderma longicauda shows an amazing temperature tolerance towards other brittle star species and is far less affected by rising water temperatures than other marine invertebrates , there are no studies to date on the effect of temperature on the larvae and development of these brittle stars, which means that future adverse effects from global warming are not can be excluded.

Individual evidence

  1. ↑ a b c Stöhr, S .; O'Hara, T .; Thuy, B. (Eds) (2019). World Ophiuroid Database. Ophioderma longicauda (Bruzelius, 1805). Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=124821 on 2019-11-30
  2. ↑ a b c Tortonese, E. (1983) Remarks on the morphology and taxonomy of Ophioderma longicaudum (Retz.) From the Mediterranean . Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano, 124, 21-28.
  3. ↑ a b c d e f g Moosleitner, H., Patzner, R. (1995) Under water guides Mediterranean - lower. Lower animals , Ed .: Naglschmid, Stuttgart
  4. ↑ a b Bruzelius, N. (1805). Dissertatio sistens species cognitas asteriarum, quamr. sub præsidio DM And. J. Retzii, pro laurea modeste exhibet Nicolaus Bruzelius. Unpublished PhD thesis, Lund University
  5. ↑ a b c d e f g h i j k l Ludwig, H., Hamann, O., Bronn, HG et al. (1901). Dr. HG Bronn's classes and orders of the animal kingdom, scientifically represented in words and pictures: Die Schlangensterne (Vol. 2, Section 3.) Echinodermen (echinoderms), Ed .: Winter; Leibzig
  6. ^ Melville, RV (1980) Opinion 1152. Ophiura Lamarck, 1801 and Ophioderma Müller & Troschel, 1840 (Ophiuroidea): ruling on application of these names. Bulletin of Zoological Nomenclature, 37, 78-80.
  7. ↑ a b c d e f g h i j k l Stöhr, S., Boissin, E., & Chenuil, A. (2009). Potential cryptic speciation in Mediterranean populations of Ophioderma (Echinodermata Ophiuroidea) . Zootaxa, 2071, 1-20.
  8. ↑ a b c d e f g h i j Riedl, R. (1970) Fauna and Flora of the Adriatic - A systematic marine guide for biologists and nature lovers (2nd edition), Ed .: Verlag Pail Parey, Hamburg
  9. ↑ a b c d e f Valentin, C., (1986), Fascinating Underwater World of the Mediterranean Sea - Insights into the marine biology of coastal habitats , Ed .: Pacini Ed. [u. a.], Pisa
  10. ↑ a b Stöhr, S., O'Hara, TD, & Thuy, B. (2012). Global diversity of brittle stars (Echinodermata Ophiuroidea) . PLoS One, 7 (3), e31940.
  11. ↑ Deschuyteneer, M., & Jangoux, M. (1978). Comportement alimentaire et structures digestives d'Ophioderma longicauda (Retzius) (Echinodermata, Ophiuroidea). In Annales de l'Institut océanographique, 54, 127-138.
  12. ↑ a b c Weber A. AT, Mérigot B., Valière S. et al. (2015) Influence of the larval phase on connectivity: strong differences in the genetic structure of brooders and broadcasters in the Ophioderma longicauda species complex. Molecular Ecology. 24: 6080-6094
  13. ↑ a b c d e f g Weber A. AT, Stöhr S. ​​and Chenuil A. (2014) Genetic data, reproduction season and reproductive strategy data support the existence of biological species in Ophioderma longicauda. Comptes Rendus Biologies. 337: 553-560
  14. ↑ McEdward, LR, & Miner, BG (2001). Larval and life-cycle patterns in echinoderms. Canadian Journal of Zoology, 79 (7), 1125-1170.
  15. ↑ a b Weber A. AT, Abi-Rached L., Galtier N., et al. (2017) Positive selection on sperm ion channels in a brooding brittle star: consequence of life-history traits evolution. Molecular Ecology. 26: 3744-3759
  16. ↑ a b Weber A. AT, Dupont S and Chenuil A. (2013) Thermotolerance and regeneration in the brittle star species complex Ophioderma longicauda: A preliminary study comparing lineages and Mediterranean basins. Comptes Rendus Biologies 336: 572-581
  17. ↑ a b Boissin E., Stöhr S. ​​and Chenuil A. (2011) Did vicariance and adaptation drive cryptic speciation and evolution of brooding in Ophioderma longicauda (Echinodermata: Ophiuroidea), a common Atlanto- Mediterranean ophiuroid? Molecular Ecology. 20 (22): 4737-4755
  18. ↑ a b Calado, R. (2006). Marine ornamental species from European waters a valuable overlooked resource or a future threat for the conservation of marine ecosystems. Scientia Marina, 70 (3), 389-398.

Web links

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