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The smalleye hammerhead or golden hammerhead (''Sphyrna tudes''), is a small species of hammerhead shark, belonging to the family Sphyrnidae. This species is common in the shallow coastal waters of the western Atlantic Ocean, from Venezuela to Uruguay. It favors muddy habitats with poor visibility, reflected by its relatively small eyes. Adult males and juveniles are schooling and generally found apart from the solitary adult females. Typically reaching in length, this shark has a unique, bright golden color on its head, sides, and fins, which was only scientifically documented in the 1980s. As in all hammerheads, its head is flattened and laterally expanded into a hammer-shaped structure called the "cephalofoil", which in this species is wide and long with an arched front margin bearing central and lateral indentations. The yellow-orange pigments of the smalleye hammerhead seem to have been acquired from the penaeid shrimp ''Xiphopenaeus kroyeri'', the main food of juvenile sharks, and from sea catfish and their eggs, the main food of adults. The golden color may serve to conceal it from predators such as larger sharks. This species is viviparous, with the developing embryos sustained by a placental connection formed from the depleted yolk sac. Females bear litters of 5–19 pups every year following a gestation period of 10 months. Reproductive seasonality, litter size, and size at maturity vary between geographical regions. Because of its abundance, the smalleye hammerhead is an economically important bycatch of artisanal gillnet fisheries throughout its range and is utilized as food. In recent years, overfishing has caused marked declines in its numbers off Trinidad, northern Brazil, and probably elsewhere. Coupled with its low reproductive rate, this has led the International Union for Conservation of Nature (IUCN) to list it under Vulnerable. ==Taxonomy and phylogeny== Despite being one of the most easily recognizable sharks, the smalleye hammerhead has had a long history of taxonomic confusion that still remains to be fully resolved.〔 Its scientific name originated in 1822, with French zoologist Achille Valenciennes' description of ''Zygaena tudes'' in the scientific journal ''Memoires du Museum National d'Histoire Naturelle''; the specific epithet ''tudes'' is Latin for "hammer". Valenciennes made reference to three specimens: one from Nice in France, one from Cayenne in French Guyana, and one from the Coromandel Coast of India.〔 However, for over two centuries taxonomists believed Valenciennes' account matched the great hammerhead, which thus became known as ''Zygaena'' (later ''Sphyrna'') ''tudes''.〔 The smalleye hammerhead was known by a different name, ''Sphyrna bigelowi'', coined by Stewart Springer in a 1944 issue of ''Journal of the Washington Academy of Sciences''.〔 In 1950, Enrico Tortonese examined the Nice and Cayenne specimens of ''S. tudes'' (the Coromandel specimen having been lost in the interim) and concluded that they were not great hammerheads but rather the same species as ''S. bigelowi''.〔 Carter Gilbert concurred in his 1967 revision of the hammerhead sharks, noting that while the lost Coromandel specimen was probably a great hammerhead, none of the existing material belonged to that species. Thus, ''Sphyrna tudes'' became the accepted name for the smalleye hammerhead, taking precedence over ''S. bigelowi'' because it was published earlier, and the great hammerhead received the next available name ''Sphyrna mokarran''. Gilbert designated the Nice specimen as the lectotype that would define ''S. tudes'', having priority over the Cayenne specimen (the paralectotype). This was meant to stabilize the name but had the opposite effect.〔〔 In 1981, Jean Cadenat and Jacques Blache revisited the type specimens of ''S. tudes'' and found that the lectotype from Nice is likely not a smalleye hammerhead but rather a fetal whitefin hammerhead (''S. couardi'', likely a synonym of the scalloped hammerhead, ''S. lewini'').〔〔 This would also explain the anomalous locality of the Nice specimen, as the smalleye hammerhead is not otherwise known outside of the Americas. By the rules of binomial nomenclature, ''Sphyra tudes'' should then become the valid name for the whitefin hammerhead, taking precedence over ''S. couardi'', and the smalleye hammerhead would revert to being ''Sphyrna bigelowi''. Taxonomists though have been reluctant to change the names again, preferring to keep the smalleye hammerhead as ''S. tudes''.〔 For this solution to have official status would require a decision by the International Commission on Zoological Nomenclature (ICZN), to reject the Nice specimen as the lectotype and designate the Cayenne specimen in its place. The relevant petition to the ICZN has not yet been put forth.〔 }} }} }} }} }} Until the first detailed study of the smalleye hammerhead was carried out in 1985–86 by José Castro of Clemson University for the Food and Agriculture Organization of the United Nations (FAO), its distinctive golden coloration was unknown to science. The color fades after death and the pigments leech into the preservative, resulting in the "yellowish cast" of museum specimens being regarded as an artifact of preservation. The names "yellow hammerhead" or "golden hammerhead" are used by fishermen in Trinidad for this shark, and the latter was promoted for wider usage by Castro.〔〔 Another common name for this species is the curry shark.〔 Phylogenetic analyses based on nuclear and mitochondrial DNA have found that the hammerheads with the smallest cephalofoils are the most derived members of their lineage. The closest relative of the smalleye hammerhead appears to be the scoophead (''S. media''), and the two of them in turn form a clade with the sister species pair of the scalloped bonnethead (''S. corona'') and the bonnethead (''S. tiburo'').〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「smalleye hammerhead」の詳細全文を読む スポンサード リンク
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