The first known specimen of the smalleye pygmy shark was a female 18 cm (7.1 in) long, caught off Donggang, Taiwan, on September 23, 1958. It was described by Taiwanese ichthyologistTeng Huo-Tu, who gave it the specific epithetalii after a woman.[2] The name subsequently came to be rendered as aliae in scientific literature. Some authors questioned the validity of the species, and in 1977 Jeffrey Alan Seigel and colleagues synonymizedS. aliae with S. laticaudus.[3] In 1987, Kunio Sasaki and Teruya Uyeno performed morphological comparisons and reaffirmed the distinctiveness of S. aliae.[4]
Distribution and habitatedit
The smalleye pygmy shark appears to be widely distributed, but in patches, in the western Pacific Ocean, having been reported from off southern Japan, the Philippines, and northern and eastern Australia. It inhabits the upper and middle layers of the water column near land, at depths of 150–2,000 m (490–6,560 ft). It conducts a diel vertical migration, spending the day in deeper water and rising to shallower waters at night.[5]
Descriptionedit
Among the smallest of extant sharks, the smalleye pygmy shark attains a maximum recorded length of 22 cm (8.7 in). It is shaped like a cigar and has a bulbous, pointed snout. The eyes are relatively small, with their diameters measuring 43–66% as long as the snout (compared to 61–82% in S. laticaudus). The eyes of this species also differ from S. laticaudus in that the upper rim of the eye socket is chevron-shaped rather than nearly straight. The nostrils lack substantially expanded skin flaps in front. The mouth is nearly transverse and bears thin lips; a pair of papillae (nipple-like structures) is on the upper lip that is absent in S. laticaudus.[4][5] There are 20–27 upper tooth rows and 18–23 lower tooth rows.[6] The upper teeth are slender and upright. The larger, broader lower teeth have angled and knife-like cusps, and interlock to form a continuous cutting surface. The five pairs of gill slits are tiny and uniform.[5][7]
The two Squaliolus species are the only sharks that have a spine on the first dorsal fin, but not the second. The spine is usually exposed in males and covered by skin in females.[3] The tiny first dorsal fin originates about over the rear tip of the pectoral fin. The second dorsal fin is long and low, and originates over the front half of the pelvic fin bases. The pectoral fins are short with rounded margins, and the pelvic fins are long and low. The anal fin is absent. The caudal peduncle is thin and bears slight lateral keels. Males have shorter abdomens and longer caudal peduncles than females. The caudal fin is broad and triangular, with nearly symmetrical upper and lower lobes and a prominent notch in the trailing margin of the upper lobe. The dermal denticles are flattened and not toothed or elevated on stalks. This species is dark brown to black in color, becoming light towards the fin margins. Its underside is covered by light-producingphotophores.[5][7]
Biology and ecologyedit
Little is known of the natural history of the smalleye pygmy shark.[1] It feeds primarily on midwater squid, krill, shrimps, and small bony fishes such as lanternfish.[5][6] The photophores on its underside may serve to camouflage its silhouette from predators by matching the downwelling light, a strategy known as "counter-illumination". Reproduction is aplacental viviparous as in other members of its family, with the young being born under 10 cm (3.9 in) long. Males attain sexual maturity around 15 cm (5.9 in) long.[5]
Human interactionsedit
The smalleye pygmy shark is infrequently caught by fisheries because of its small size, and has no economic value. This, coupled with its wide range, has led the IUCN to list it as Least Concern.[1]
Referencesedit
^ abcKyne, P.M.; Heupel, M.R. (2015). "Squaliolus aliae". IUCN Red List of Threatened Species. 2015: e.T41858A68643995. doi:10.2305/IUCN.UK.2015-4.RLTS.T41858A68643995.en. Retrieved 13 November 2021.
^Teng H.T. (1959). "Studeis [sic] on the elasmobranch fishes from Formosa. Pt. 4. Squaliolus alii, a new species of deep sea squaloid shark from Tung-Kang, Formosa". Report – Laboratory of Fishery Biology, Taiwan Fisheries Research Institute. 8: 1–6.
^ abSeigel, J.A.; T.W. Pietsch; B.H. Robison & T. Abe (November 25, 1977). "Squaliolus sarmenti and S. alii, Synonyms of the Dwarf Deepsea Shark, Squaliolus laticaudus". Copeia. 1977 (4): 788–791. doi:10.2307/1443196. JSTOR 1443196.
^ abSasaki K. & Uyeno T. (1987). "Squaliolus aliae, a dalatiid shark distinct from S. laticaudus". Japanese Journal of Ichthyology. 34 (3): 373–376.
^ abcdefLast, P.R. & J.D. Stevens (2009). Sharks and Rays of Australia (second ed.). Harvard University Press. p. 104. ISBN978-0-674-03411-2.
^ abTanakamaru H.; Shibuya T. & Kubota T. (1999). "Some Biological Aspects of the Spined Pygmy Shark, Squaliolus aliae, from Suruga Bay, Japan". Journal of the Faculty of Marine Science and Technology, Tokai University (48): 51–67.
^ abCompagno, L.J.V. (1984). Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date. Rome: Food and Agricultural Organization. p. 108–109. ISBN92-5-101384-5.
April 12, 2024
smalleye, pygmy, shark, smalleye, pygmy, shark, squaliolus, aliae, little, known, species, squaliform, shark, family, dalatiidae, found, water, deep, near, japan, philippines, australia, migrates, vertically, daily, spending, deep, water, night, shallower, wat. The smalleye pygmy shark Squaliolus aliae is a little known species of squaliform shark in the family Dalatiidae found in water 150 2 000 m 490 6 560 ft deep near Japan the Philippines and Australia It migrates vertically daily spending the day in deep water and the night in shallower water One of the smallest shark species the smalleye pygmy shark is known to reach only 22 cm 8 7 in long It has a blackish spindle shaped body with relatively small eyes and a spine preceding the first dorsal fin but not the second Bioluminescent photophores occur on its underside which may serve to disguise its silhouette from predators This species feeds on small squid krill shrimp and bony fishes It is aplacental viviparous The International Union for Conservation of Nature has assessed it as Least Concern citing its wide distribution and lack of threat from fisheries Smalleye pygmy sharkConservation statusLeast Concern IUCN 3 1 1 Scientific classificationDomain EukaryotaKingdom AnimaliaPhylum ChordataClass ChondrichthyesSubclass ElasmobranchiiSubdivision SelachimorphaOrder SqualiformesFamily DalatiidaeGenus SqualiolusSpecies S aliaeBinomial nameSqualiolus aliaeTeng 1959Range of smalleye pygmy shark Contents 1 Taxonomy 2 Distribution and habitat 3 Description 4 Biology and ecology 5 Human interactions 6 ReferencesTaxonomy editThe first known specimen of the smalleye pygmy shark was a female 18 cm 7 1 in long caught off Donggang Taiwan on September 23 1958 It was described by Taiwanese ichthyologist Teng Huo Tu who gave it the specific epithet alii after a woman 2 The name subsequently came to be rendered as aliae in scientific literature Some authors questioned the validity of the species and in 1977 Jeffrey Alan Seigel and colleagues synonymized S aliae with S laticaudus 3 In 1987 Kunio Sasaki and Teruya Uyeno performed morphological comparisons and reaffirmed the distinctiveness of S aliae 4 Distribution and habitat editThe smalleye pygmy shark appears to be widely distributed but in patches in the western Pacific Ocean having been reported from off southern Japan the Philippines and northern and eastern Australia It inhabits the upper and middle layers of the water column near land at depths of 150 2 000 m 490 6 560 ft It conducts a diel vertical migration spending the day in deeper water and rising to shallower waters at night 5 Description editAmong the smallest of extant sharks the smalleye pygmy shark attains a maximum recorded length of 22 cm 8 7 in It is shaped like a cigar and has a bulbous pointed snout The eyes are relatively small with their diameters measuring 43 66 as long as the snout compared to 61 82 in S laticaudus The eyes of this species also differ from S laticaudus in that the upper rim of the eye socket is chevron shaped rather than nearly straight The nostrils lack substantially expanded skin flaps in front The mouth is nearly transverse and bears thin lips a pair of papillae nipple like structures is on the upper lip that is absent in S laticaudus 4 5 There are 20 27 upper tooth rows and 18 23 lower tooth rows 6 The upper teeth are slender and upright The larger broader lower teeth have angled and knife like cusps and interlock to form a continuous cutting surface The five pairs of gill slits are tiny and uniform 5 7 The two Squaliolus species are the only sharks that have a spine on the first dorsal fin but not the second The spine is usually exposed in males and covered by skin in females 3 The tiny first dorsal fin originates about over the rear tip of the pectoral fin The second dorsal fin is long and low and originates over the front half of the pelvic fin bases The pectoral fins are short with rounded margins and the pelvic fins are long and low The anal fin is absent The caudal peduncle is thin and bears slight lateral keels Males have shorter abdomens and longer caudal peduncles than females The caudal fin is broad and triangular with nearly symmetrical upper and lower lobes and a prominent notch in the trailing margin of the upper lobe The dermal denticles are flattened and not toothed or elevated on stalks This species is dark brown to black in color becoming light towards the fin margins Its underside is covered by light producing photophores 5 7 Biology and ecology editLittle is known of the natural history of the smalleye pygmy shark 1 It feeds primarily on midwater squid krill shrimps and small bony fishes such as lanternfish 5 6 The photophores on its underside may serve to camouflage its silhouette from predators by matching the downwelling light a strategy known as counter illumination Reproduction is aplacental viviparous as in other members of its family with the young being born under 10 cm 3 9 in long Males attain sexual maturity around 15 cm 5 9 in long 5 Human interactions editThe smalleye pygmy shark is infrequently caught by fisheries because of its small size and has no economic value This coupled with its wide range has led the IUCN to list it as Least Concern 1 References edit a b c Kyne P M Heupel M R 2015 Squaliolus aliae IUCN Red List of Threatened Species 2015 e T41858A68643995 doi 10 2305 IUCN UK 2015 4 RLTS T41858A68643995 en Retrieved 13 November 2021 Teng H T 1959 Studeis sic on the elasmobranch fishes from Formosa Pt 4 Squaliolus alii a new species of deep sea squaloid shark from Tung Kang Formosa Report Laboratory of Fishery Biology Taiwan Fisheries Research Institute 8 1 6 a b Seigel J A T W Pietsch B H Robison amp T Abe November 25 1977 Squaliolus sarmenti and S alii Synonyms of the Dwarf Deepsea Shark Squaliolus laticaudus Copeia 1977 4 788 791 doi 10 2307 1443196 JSTOR 1443196 a b Sasaki K amp Uyeno T 1987 Squaliolus aliae a dalatiid shark distinct from S laticaudus Japanese Journal of Ichthyology 34 3 373 376 a b c d e f Last P R amp J D Stevens 2009 Sharks and Rays of Australia second ed Harvard University Press p 104 ISBN 978 0 674 03411 2 a b Tanakamaru H Shibuya T amp Kubota T 1999 Some Biological Aspects of the Spined Pygmy Shark Squaliolus aliae from Suruga Bay Japan Journal of the Faculty of Marine Science and Technology Tokai University 48 51 67 a b Compagno L J V 1984 Sharks of the World An Annotated and Illustrated Catalogue of Shark Species Known to Date Rome Food and Agricultural Organization p 108 109 ISBN 92 5 101384 5 Retrieved from https en wikipedia org w index php title Smalleye pygmy shark amp oldid 1218187962, wikipedia, wiki, book, books, library,
