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The Chaetognatha or chaetognaths are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, about 20% of the known Chaetognatha species are benthic, and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange. They range in size from 2 to 120 millimetres.
Viverravidae is an extinct family within the clade Carnivoramorpha. They are related to carnivorans, and lived from the early Palaeocene to the Eocene.
Eukrohniidae is a family of sagittoideans in the order Phragmophora. It consists of a single genus, Eukrohnia von Ritter-Záhony, 1909.
Viviparus georgianus, common name the banded mystery snail, is a species of large freshwater snail with gills and an operculum, an aquatic gastropod mollusk in the family Viviparidae, the river snails.
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Gnathifera is a clade of generally small spiralians characterized by complex jaws made of chitin. It comprises the phyla Gnathostomulida, Rotifera, Micrognathozoa, and Chaetognatha. It may also include the Cycliophora.
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Sagittidae is a family of sagittoideans in the order Aphragmophora.
Phragmophora is an order of sagittoideans in the phylum Chaetognatha.
Heterokrohniidae is a family of sagittoideans in the order Phragmophora.
Krohnittellidae is a family of sagittoideans in the order Phragmophora. It consists of one genus, Krohnittella Germain & Joubin, 1912.
Krohnittidae is a family of chaetognaths in the order Aphragmophora. It consists of a single genus, Krohnitta von Ritter-Záhony, 1910.
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Archeterokrohnia is a genus of chaetognaths in the family Heterokrohniidae.The total body length excluding tail fin 28.5; the tail section is 55.2% of the tail fin; head blunt when hooded, triangular after preservation, head with 3.5 mm. Furthermore, the eyes are absent, the trunk section is orange throughout in life, and the organism exists around 3200 m below sea level.
Eukrohnia fowleri is a deep-sea marine arrow worm. It is the only known bioluminescent member of the genus Eukrohnia, and one of the two known species of bioluminescent arrow worms, the other being the distantly related Caecosagitta macrocephala. The bioluminescent organ of Eukrohnia Fowlery is found along the center of its tail fin on both its dorsal and ventral side. It has a secreted bioluminescence that is thought to be coelenterazine based. While both species use luciferases in conjunction with coelenterazine for light emission, the luciferase of Eukrohnia fowleri is highly stable after 30 minutes while the luciferase of Caecosagitta macrocephala becomes inactive. So far, there is no other bioluminescent organism that uses hexagonal packing in order to hold bioluminescent materials/ E. fowleri evolved through the adaptation to hypoxic water and due to the recent oxygenation of water they have been experiencing bottleneck events. These events have been seen as one of the reasons that E. fowleri have such low biodiversity.
Xenokrohnia is a genus of chaetognaths in the family Heterokrohniidae. It consists of one species, Xenokrohnia sorbei Casanova, 1993, which lives in a marine environment. The initial discovery was made from six specimens found in a deep-sea search in the Bay of Biscay for Spadella equidentata Casanova, 1987. A uniquely large (ventral) secretory gland, separate from other chaetognaths, defined the new genus and species. The gland, which is likely used to rid the body of digestive fluids, is probably due to the unique feeding habits of the species; these may include scavenging habits. The presence of an unusual and seemingly superfluous digestive utility is similar to Archeterokrohnia palpifera Casanova, 1986, which have a larger pair of pedipalps then what is common for chaetognaths.
Calispadella is a genus of chaetognaths in the family Spadellidae. It consists of one species, Calispadella alata Casanova & Moreau, 2005. It is differentiated from other species of Spadellidae by the presence of an unusually long tail segment and a rare aspect of the lateral fins, similar to that of Paraspadella gotoi Casanova, 1990. The species is noted by the complete development of seminal vesicles in juveniles and the use of lateral fins for buoyancy in the deep-sea waters where the specimens were found. It was the first to be described exclusively in the range of deep-sea hydrothermic vents.
Hemispadella is a genus of chaetognaths in the family Spadellidae. It consists of one species, Hemispadella dauvini Casanova, 1996. The species, as the generic name implies, shares numerous, but not all, of the characteristics of Spadellidae; it shares a number of other characteristics with Heterokrohniidae. The ventral ganglion, poorly described in chaetognaths, is of similar size to the Heterokrohniidae, and the larger number of teeth, and the difference in appearance and function between the anterior and posterior teeth, are similarly characteristic. The relative tail size is similar to that of the Spadellidae, although the overall size is unprecedented among the Spadellidae. The more developed nature of transverse musculature and the basis for the lateral fins are as those of Spadellidae, as well.
Paraspadella is a genus of chaetognaths in the family Spadellidae. Paraspadella was originally considered as Spadella before a revision separated that genus into three genera: Spadella, Paraspadella, and Gephyrospadella, the last of which is now synonymised to Paraspadella. The initial division was based on previous knowledge of three groups of Spadella, in a similar manner in which Sagitta was divided into a family of genera. Paraspadella is differentiated from Spadella by the presence of disparate (digital) adhesive organs, present in the former to various degrees, but entirely absent in the latter.
References
- 1 2 von Ritter-Záhony, R. (1911). Revision der Chatognathen. Deutsche Südpolar Expedition, 1901–1903, 13, 1–71.
- 1 2 Casanova, J. (1992). Chaetognaths from Alvin dives in the Santa Catalina Basin (California), with description of two new Heterokrohnia species. Journal of Natural History, 26(3), 663–674.
- 1 2 3 Casanova, J. (1994). Three new rare Heterokrohnia species (Chaetognatha) from deep benthic samples in the northeast Atlantic. Proceedings of the Biological Society of Washington, 107(4), 743–750.
- ↑ Marumo, R. & Kitou, M. (1966). A new species of Heterokrohnia (Chaetognatha) from the western north Pacific. La Mer, 4(3), 24–29.
- 1 2 3 4 Casanova, J. (1986). Quatre nouveaux Chaetognathes atlantiques abyssaux (genre Heterokrohnia): description, remarques éthologiques, et biogéographiques. Oceanologica Acta, 9(4), 469–477.
- 1 2 Kapp, H. & Hagen, W. (1985). Two new species of Heterokrohnia (Chaetognatha) from Antarctic waters. Polar Biology, 4(1), 53–59.
- ↑ Casanova, J. & Chidgey, K. (1987). Une nouvelle espèce d'Heterokrohnia (Chaetognathe) des campagnes du “Discovery” dans l'Atlantique nord-oriental. Bulletin du Muséum National d'Histoire Naturelle, Paris, (4)9(A)(4), 879–885.
- ↑ Dawson, J. K. (1968). Chaetognaths from the Arctic basin, including the description of a new species of Heterokrohnia. Bulletin of the Southern California Academy of Sciences, 67(2), 112–124.
- ↑ Casanova, J. & Chidgey, K. (1990). A new benthopelagic species of Heterokrohnia (Chaetognatha) from the north Atlantic Ocean. Bulletin Zoo..logisch Museum, 12(8), 109–116.
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