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Lamniformes - Accessscience from Mcgraw-Hill Education Page 1 of 6 Lamniformes - AccessScience from McGraw-Hill Education Page 1 of 6 Lamniformes Article by: Boschung, Herbert Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097-8542.803390 (http://dx.doi.org/10.1036/1097-8542.803390) Content • Odontaspidae (sand tiger sharks) • Mitsukurinidae (goblin sharks) • Pseudocarchariidae (crocodile sharks) • Megachasmidae (megamouth shark) • Alopiidae (thresher sharks) • Cetorhinidae (basking sharks) • Lamnidae (mackerel sharks) • Bibliography • Additional Readings An order of sharks distinguished from all other sharks by the following combination of characters: trunk cylindrical; head conical to cylindrical, not laterally expanded; two dorsal fins, lacking spines; five gill slits, all anterior to the pectoral fin base or the last two above the pectoral fin base; mouth large, its gape extending well beyond the eyes; spiracles usually present, small and well behind the eyes; eyes without a nictitating membrane; barbels absent; and ring-type intestinal valve. Lamniform sharks are ovoviviparous. Fertilized eggs are enclosed in egg cases in the oviducts (uteri), where they undergo embryonic development, ordinarily from the energy supplied by the yolk. Although the reproductive event may begin with each uterus containing about 20 fertilized eggs, normally only one or two in each uterus reach full term. The gross loss of potential progeny is explained by oophagy or uterine cannibalism, an uncommon phenomenon in which the largest (and presumably oldest) fetuses are free in the uterus to feed on the remaining eggs and developing embryos, thus cannibalizing their potential siblings. This reproductive strategy sacrifices numbers for a few large, strong pups that are like small adults, ready to fend for themselves. See also: Elasmobranchii (/content/elasmobranchii/214800); Selachii (/content/selachii/613500) Lamniformes comprises only 15 extant species in seven families (see illustration), four of which are monotypic. http://www.accessscience.com/content/lamniformes/803390 7/21/2015 Lamniformes - AccessScience from McGraw-Hill Education Page 2 of 6 Representatives of seven Lamniformes families. (a) Odontaspidae. (b) Mitsukurinidae. (c) Pseudocarchariidae. (d) Megachasmidae. (e) Alopiidae. (f) Cetorhinidae. (g) Lamnidae. (From J. S. Nelson, Fishes of the World, 4th ed., Wiley, New York, 2006) Odontaspidae (sand tiger sharks) Sand tiger sharks are distinguished by gill openings that are all in front of the pectoral fin; large teeth with slender cusps and lateral cusplets; a compressed caudal peduncle, without a lateral keel but with an upper precaudal pit; and an asymmetrical caudal fin with a relatively short ventral lobe. Females are the larger of the sexes, with a maximum total length of 370 cm (12 ft). http://www.accessscience.com/content/lamniformes/803390 7/21/2015 Lamniformes - AccessScience from McGraw-Hill Education Page 3 of 6 The family comprises two genera, Carcharias with one species and Odontaspia with two species. The snout is short and flattened in Carcharias, and long and conical in Odontaspia; dorsal, anal, and pelvic fins are about the same size in Carcharias, whereas the first dorsal is larger than the second, and the second is larger than the anal, in Odontaspia. Odontaspids are known from tropical to cool-temperate zones of the Atlantic, Indian, and Pacific oceans, from continental and insular shores to the outer shelves and slopes to about 1600 m (5250 ft). They are voracious feeders on a wide variety of bony fishes, other sharks, rays, squids, and bottom crustaceans. Schools of sand tigers have been observed cooperatively surrounding and bunching schooling prey and then feeding on them. Of the three species, Carcharias taurus is by far the best known biologically. The gestation period is 8 to 9 months and the newly born are 95–105 cm (37–42 in.) in total length. Relatively few attacks by these sharks on people have been recorded, but any large shark should be regarded as potentially dangerous and should not be harassed or provoked. Mitsukurinidae (goblin sharks) This family consists of only one extant species, Mitsukurina owstoni, a bizarre shark that occurs in apparently disjunct populations in the eastern and western Atlantic (including the Gulf of Mexico), off South Africa, in the eastern Pacific (including southern California), and off southern Australia. It is easily recognized by an elongated and flattened snout; small eyes; soft flabby body and fins; very protrusible jaws; teeth with long slender cusps and no cusplets; dorsal fins about equal in size, and smaller than anal and pectoral fins; no precaudal pit; and caudal fin without a ventral lobe. Maximum length is 3.8 m (12.5 ft). The goblin shark is an uncommon, poorly known, bottom-dwelling shark that inhabits outer continental shelves and beyond to at least 550 m (1800 ft), but rarely occurs near shore. Very little is known of its biology; however, its morphology suggests a relatively inactive, slow-swimming shark that probably uses its sensitive snout to detect prey and its highly protractile jaws to reach out and seize the prey, which may be squid, shrimp, crabs, or a variety of fishes. Pseudocarchariidae (crocodile sharks) This is a monotypic family, represented by Pseudocarcharias kamoharai, which occurs in scattered localities, usually oceanic, in tropical and subtropical waters of the Northern and Southern hemispheres. It has a slender spindle-shaped body; long gill slits that reach dorsally past the axis of the body; highly protrusible jaws that are equipped with long slender teeth; angular dorsal fins; a prominent ventral caudal fin lobe; exceptionally large eyes; upper and lower precaudal pits; and a low lateral keel. This is the smallest lamniform shark, with a maximum adult length of 110 cm (43 in.); it is 41 cm (16 in.) at birth. Megachasmidae (megamouth shark) http://www.accessscience.com/content/lamniformes/803390 7/21/2015 Lamniformes - AccessScience from McGraw-Hill Education Page 4 of 6 This monotypic family, represented by Megachasma pelagios, was discovered in 1976 off Oahu, Hawaii. Since then, 35 more specimens have been captured in scattered places in warm temperate and tropical shallow coastal waters [depth: 5 m (16 ft)] to oceanic waters, where it inhabits the epipelagic zone (the illuminated surface zone) to depths of 166 m (545 ft). Megamouth is a very distinctive shark in having a large terminal mouth; large head; cylindrical and somewhat compressed trunk; snout that is exceptionally short but broadly rounded; moderately long gill slits, the last two over the pectoral fin base; upper and lower precaudal pits; small teeth in numerous rows; and gill rakers in the form of fingerlike dermal papillae. At a maximum length of 5.5 m (18 ft), megamouth is the smallest of the three giant filter-feeding sharks, the others being the basking shark [10 m (33 ft) or more] and the whale shark [12 m (39 ft) or more]. Alopiidae (thresher sharks) Thresher sharks are easily distinguished by the greatly elongate and curved upper caudal fin lobe, which is about half their total length; long narrow pectoral fins; relatively small gill slits, with the third to fifth over the origin of the pectoral fin; large eyes; a small mouth; precaudal pits; and a caudal peduncle without keels. Maximum length is 5.7 m (18.7 ft). Thresher sharks occur practically circumglobally in temperate to tropical waters from coastal to oceanic regions. They feed on a variety of schooling fishes, such as mackerels and herrings, as well as squids, octopuses, and pelagic crustaceans. The long caudal fin is used to herd fishes and to slash through a school, killing or stunning prey to be consumed later. There is one genus with three species: Alopias pelagicus (pelagic thresher), 347 cm (11 ft) total adult length, 96 cm (38 in.) at birth; A. superciliosus (bigeye thresher), 488 cm (16 ft) total adult length, 105 cm (41 in.) at birth; and A. vulpinus (thresher shark), 760 cm (25 ft) total adult length, 150 cm (59 in.) at birth. Cetorhinidae (basking sharks) Cetorhinidae is another monotypic family, which is represented by the basking shark (Cetorhinus maximus). It occurs on continental and insular shelves, offshore and often close to land, just free of the surf zone, in boreal (northern) to warm temperate waters of the Atlantic and Pacific oceans. It is easily distinguished from other sharks by the following combination of characters: exceptionally large gill openings practically encircling the head and all in front of the pectoral fin; hairlike gill rakers of modified dermal denticles on the gill arches; very small and hooklike teeth; nearly lunate caudal fin, with a well-developed lower lobe; precaudal pits; and caudal peduncle with strong lateral keels. The basking shark is a filter feeder, but its method differs from the other two huge filter-feeding sharks (megamouth and whale shark), as it passively strains plankton while swimming with mouth agape and external gill slits open, as opposed to pumping or gulping water into the pharynx and force-expelling it across the gill rakers. The basking shark is the world's second largest living fish, reportedly reaching 15 m (49 ft) in total length, but specimens exceeding 10 m (33 ft) are exceptional. Size at birth is unknown; however, the smallest known free-living basking shark measured 165 cm (65 in.). http://www.accessscience.com/content/lamniformes/803390 7/21/2015 Lamniformes - AccessScience from McGraw-Hill Education Page 5 of 6 Lamnidae (mackerel sharks) Mackerel sharks occur virtually globally from nearshore and the continental shelf to epipelagic zones of cold- temperate to tropical waters. They are distinguished from other sharks by the following combination of characters: fusiform body moderately slender to robust; snout moderately long, pointed, and conical; large gill openings, extending above the axis of the body (except in Lamna) and all in front of the pectoral fin base; no gill rakers on the gill araches; first dorsal fin large, high, erect, and angular or somewhat rounded; second dorsal and anal fins very small; caudal fin lunate or crescent-shaped and caudal peduncle with distinct keels.
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