Squaliformes

(Dogfish sharks)

Class Chondrichthyes

Order Squaliformes

Number of families 7

Evolution and systematics

The order Squaliformes contains 22 genera, 98 formally described species, and at least 17 known but undescribed species. However, higher-level systematics is not pure science, and hence it should not be surprising that experts may define the order Squaliformes somewhat differently. Some do not include the bramble sharks, Echinorhinidae, and others exclude additional groups, justifying their decisions on various fine morphological details. In this chapter, we will consider the order Squaliformes to comprise a more traditional and inclusive group of sharks, which includes the bramble sharks (Echinorhinidae), the dogfish sharks (Squalidae), the gulper sharks (Centrophoridae), the lantern sharks (Etmopteridae), the sleeper sharks (Somniosidae), the rough sharks (Oxynotidae), and the kitefin sharks (Dalatiidae). Fossils interpreted as representing Squaliformes have been laid down in deposits at least 150 million years old, and future discoveries will surely push this trail marker back deeper into the past. Amongst living elasmobranches, Squaliformes is usually accepted as a sister group to an evolutionary branch consisting of angel sharks (Squatiniformes), saw sharks (Pristiophoriformes), and rays. Defining membership within Squaliformes based on an unshared morphological character is not possible, and thus crafting a membership card for this order of fishes may have to await the results of molecular studies.

Physical characteristics

Squaliformes includes fishes that rank as the smallest and amongst the largest of all living sharks, from spined pygmy sharks (Squaliolus) growing only to about 10 in (25.4 cm) long, to Greenland sharks (Somniosus microcephalus) and Pacific sleeper sharks (S. pacificus) estimated at over 20 ft (6.1 m) long. These sharks are a mixed lot; however, and a general diagnosis of their physical characteristics includes: body obviously sharklike, with a cylindrical trunk; snout pointed to bluntly conical and possibly depressed; head not laterally expanded; small-to-large eyes on side of head without nictitating membranes; teeth in top and bottom jaws similar or different; teeth only moderately different along a jaw; bottom teeth always with sharp cutting edge; spiracles present and sometimes large; five pairs of small gill openings just anterior to pectoral fins; pectoral fins small-to-moderate in size; two low-to-high dorsal fins with spines, as in Squalus, Etmopterus, and Oxynotus species or without spines as in Isistius, Somniosus, and Eupotmicroides species; pelvic fins small to moderate in size; anal fin absent; and caudal fin with or without dorsal notch and with ventral lobe shorter than dorsal lobe when present. At maximum size, males are generally smaller than their corresponding females. Species such as the piked dogfish (Squalus acanthias), which inhabit relatively shallow waters, may be counter shaded with lighter bellies, whereas those such as the pygmy shark (Euprotomicrus bispinatus) may be more uniform and dark. Luminous organs are possessed by a handful of species, representing genera such as Oxynotus, Isistius, Etmopterus, and Centroscyllium.

Distribution

Representatives of Squaliformes occur in all oceans. Most species are residents of temperate or tropical latitudes, where they inhabit nearshore waters associated with continental and insular shelves and slopes.

Habitat

Squaliformes are primarily found in marine environments; however, some species, such as the piked dogfish, can occasionally operate in estuarine waters. The Greenland shark has also been captured in rivers far from the sea. Such occurrences most likely represent sharks that have temporarily invaded upstream reaches by navigating the saltwater wedges associated with relatively deep tidal rivers. Squaliformes is a unique order of sharks in that at least one representative, the Greenland shark, is a common inhabitant of polar waters. Although some Squaliformes are found in the shallows, another general distinction of these sharks is their deep-water representation. In fact, most species of deep-water sharks are squaliforms, and some of them have been observed inhabiting abyssal depths. Because of this representation, it is likely that our understanding of the overall distribution of squaliforms will continue to expand as more resources are devoted to deep-sea exploration.

Behavior

Given their deep-water habitats, observations of many dogfish sharks in their natural surroundings only exist as valuable glimpses obtained with remote cameras and manned or unmanned deep-sea vehicles. Some species, such as many Squalus dogfishes, commonly roam in sizeable packs; other deep-water species, such as the lantern sharks (Etmopterus), probably live more solitary lives. Shark species such as the piked dogfish appear quite purposeful in their hunting activities, schooling like a marine wolf pack and devastating a wide variety of prey. Others, such as some rough sharks (Oxynotus) observed in deep water, seem more calculating and less voracious. A handful of these sharks, including the Greenland shark, Pacific sleeper shark, and piked dogfish, are known from both deep water and the shallows, and the cookie-cutter shark (Isistius brasiliensis) is thought to undertake diurnal vertical migrations in its oceanic realm. Overall, little is known about the migrations or lack thereof of most of dogfish sharks; although individuals of species such as the piked dogfish have been known to travel great distances throughout their lives.

Feeding ecology and diet

The feeding ecology of squaliforms spans that of species that feed as generalists, such as many of the dogfishes that comprise the genera Squalus, Centrophorus, and Etmopterus, to specialists such as the cookie-cutter sharks (Isistius). Because of the small size of many squaliforms, it is not surprising that small fishes and invertebrates such as various squids often make up their diet. However, their diets do include some surprises, as species such as the cookie-cutter sharks take mouthfuls from large marine animals, and huge Greenland sharks have been found with hazelnut-sized snails in their stomachs. In addition, some species, such as the Greenland shark and Pacific sleeper shark, appear to specialize somewhat by occasionally feeding on carrion, with the latter species having been filmed in deep water feeding on a decaying whale fall. The teeth of most squaliforms are not very impressive in regard to size; but they are typically well adapted for biting chunks from prey. The exceptions to this are the cookie-cutter sharks, whose teeth are proportionally some of the largest of any sharks. Little to nothing is known about the growth rate of most squaliforms, although some species grow less than 1 in (2.5 cm) per year. Similarly, the longevity of most squaliforms is unknown; however, some species are estimated to live for over 40 and possibly over 100 years. Dogfish sharks are preyed on by other sharks, teleosts, marine mammals, and humans.

Reproductive biology

The reproductive biology of these sharks is poorly known, with much knowledge stemming from several well-known species such as the piked dogfish. As in all elasmobranches, fertilization is internal, and it is suspected that all squaliforms are ovoviviparous, giving birth to live young that derive their embryonic nourishment from egg yolk, rather than from a more intimate and placenta-like maternal connection. Litters of these sharks typically yield six to 10 pups, with neonates of various species ranging from about 3–16 in (7.6–40.6 cm) long. Nursery areas are known or suspected for at least some species.

Conservation status

Three dogfish sharks are included on the IUCN Red List: the gulper shark (Centrophorus granulosus) is categorized as Vulnerable, the kitefin shark (Dalatias licha) as Data Deficient, and the piked dogfish (Squalus acanthias) as Lower Risk/Near Threatened. Because these sharks grow slowly and have a low reproductive output, fisheries should be able to overexploit them more easily than is possible with many other fishes. A report on the conservation status of 75 species of squaliforms published in 1999 noted 60% to be unexploited by fisheries. Of these, many are relatively small, deep-water forms such as the lantern sharks. Of the exploited species, 74% were categorized as species of unknown conservation status due to lack of information. Species in this group included many relatively deep-water forms such as gulper sharks (Centrophorus). The kitefin shark and the Greenland shark were considered exploited species that have limited reproductive potential and other life-history characteristics that make them especially vulnerable to overfishing. The bramble shark (Echinorhinus brucus) and the piked dogfish were considered the most imperiled of all squaliforms, falling into a conservation category comprised of species associated with historical declines in catches that have sometimes resulted in their being considered locally rare. Because many squaliforms live in relatively deep waters and catch statistics are lacking for many of them, the above conservation review must be deemed preliminary. But to be sure, there can be little doubt that heavily fished species such as the piked dogfish appear to be exploited to the maximum or overexploited throughout much of their range, and that fisheries management plans, some of which are being developed, will be needed to sustain fished populations. Little is known regarding the effects of pollution and habitat destruction on these sharks; however, several studies have indicated some squaliforms to be heavily polluted by such chemicals as PCBs and the pesticide DDT.

Significance to humans

In summing up the significance of squaliforms to humans, it is not an exaggeration to say that these sharks have probably been more fully utilized than any other group of sharks, and possibly more so than any other group of fishes. Historically squaliforms have played a role in myth, art, cultural rituals, and medicine. They have been utilized to feed people and domestic animals throughout the world. Oil extracted from their livers has served as lantern fuel, as a cosmetic additive, and as a machine-gun lubricant. The skin of squaliforms has been used as a natural type of sandpaper, and the hides of these fishes have been tanned into durable leather. Shark teeth have been used in various ceremonial art objects, as well as functioning as cutting tools. Studies of one species in particular, the piked dogfish, have facilitated the education of countless millions of biology students and have also been responsible for a great wealth of biological understanding regarding vertebrate physiology. And surprising to many, some of these species have and are being used as bait to catch lobsters and other more desirable species of sharks. There is no authenticated record of an attack on a human by any dogfish shark, although their vicious dorsal spines have certainly painfully lanced many fishermen. Furthermore, at some times and in some areas various squaliforms have posed a great nuisance to fishing operations and have destroyed valuable fishing gear.

Species accounts

List of Species

Cookie-cutter shark

Isistius brasiliensis

family

Dalatiidae

taxonomy

Scymnus brasiliensis Quoy and Gaimard, 1824, Brazil.

other common names

English: Luminous shark; French: Squalelet féroce; Spanish: Tollo cigarro.

physical characteristics

A small shark; females about 22 in (56 cm), males seldom longer than 16.5 in (42 cm). Body shaped like torpedo cigar, widest at about midpoint and tapered most along posterior length, dorsal surface of head slightly depressed. Snout short, eyes large, mouth with fleshy lips, massive lower jaw bearing functional edge of 25–31 large triangular teeth in a row, large spiracles located atop head behind eyes, gill slits small, pectoral fins small, two small spineless dorsal fins of approximately same size set far back on body, anal fin lacking, caudal fin prominent with nearly symmetrical lobes. Body brownish, darker dorsally than ventrally, distinctive dark collar band encircling body at level of gills, trailing margins of fins translucent. Luminescent organs casting a bright greenish glow cover ventral surface of trunk with exception of fins and dark collar band.

distribution

Oceanic, reported from the Indian, Pacific, and Atlantic Oceans, scattered widely throughout tropical latitudes. Less frequently reported from warm temperate regions, sometimes in association with oceanic islands.

habitat

Based on fishing data, utilizes a fair vertical swatch of its potential environment. Has been captured at the surface, often at night, but also seems well represented at depths between 279–11,482 ft (85–3,500 m). Based on this information and a limited knowledge of its behavior, this species may undergo diurnal bathypelagic to epipelagic migrations associated with feeding.

behavior

Few behavioral observations exist in nature. Thought to occasionally form loose aggregations of individuals and to be a slow swimmer. Based on characteristic craterlike wounds on organisms such as marine mammals and large fishes, as well as matching plugs of tissue from stomachs of captured cookie-cutter sharks, the species is thought to feed on large prey organisms by cleanly biting a mouthful of tissue from its victims before they swim off otherwise unharmed. Because of this, the species has been considered both micropredator and parasite; technically it should be labeled a facultative parasite because it also consumes smaller prey items in their entirety.

Explanations as to how these sharks attack large organisms have been advanced since at least the mid-1800s. As of 2002, a

popular explanation points to a hunting method that employs deceit: the sharks use their luminescent abilities to counter-illuminate and camouflage their ventral surface so that the striking dark collar band near the head assumes the appearance of a small prey item. Large predators drawing near to investigate this potential meal are eventually met with a quick bite before they can speed off. As convincing as this explanation may seem, it must be considered speculation until supported by observation.

feeding ecology and diet

Feeds on a variety of invertebrates and vertebrates, presumably using two behaviors: eats relatively small prey items, such as squids, crustaceans, and bristlemouths, whole or entirely in pieces; eats large prey, such as megamouth sharks, marlins, tunas, wahoos, dolphins, and other cetaceans, dugongs, and pinnipeds, by removing a single mouthful. This flexibility works well, especially in light of its oceanic distribution, where similar predators profit from the vertical and horizontal movements of prey organisms of varying sizes. It is not known if this species is routinely preyed upon by others.

reproductive biology

Males mature at 15 in (38 cm); females at 15.7–18.9 in (40–48 cm). Little first-hand information is known regarding the reproductive biology; but fertilization is presumably internal and development ovoviviparous. Although gestation period, number of embryos per litter, and size at birth are unknown, 6–12 eggs have been observed in the uteri of some specimens. Distributions of smaller sharks near oceanic islands have prompted some biologists to propose that young are born in coastal areas.

conservation status

Not threatened.

significance to humans

Because of its small size and scattered distribution, this shark has had little fishery value. It has been reported that this vicious shark has attacked castaways and even a scuba diver; but there is little hard evidence for this. Nonetheless, given its habit of attacking prey much larger than itself, it is likely that some adventurous diver operating offshore at night will eventually be bitten. In addition, based upon characteristic bitelike holes in the neoprene boot of a hydrophone mast, this species has been implicated in otherwise uneventful attacks on a U.S. nuclear submarine. Such attacks aside, the primary significance of this species to humans lies in its ability to astound with its ferocious design and devious behavior.

Greenland shark

Somniosus microcephalus

family

Somniosidae

taxonomy

Squalus microcephalus Bloch and Schneider, 1801, glacial seas ("Habitat in mari glaciali").

other common names

English: Ground shark, gray shark, gurry shark, sleeper shark; French: Laimargue du Groenland, leiche; German: Eishai; Spanish: Tollo de Groenlandia; Dutch: Apekalle, havkel; Inuktitut: Ekalugssuak, eqaludjuaq, iqalugjuaq; Norwegian: Haakjaerring.

physical characteristics

Large, stocky species; females at least 21 ft (6.4 m) and weighing 2,250 lb (1,020 kg), males typically smaller but at least 11 ft (3.3 m). Body "torpedo" shaped, head conical with blunt snout bearing large olfactory openings, body widest at about level of pectoral fins, eyes often infected by conspicuous parasitic copepods, spiracles obvious, mouth suctoral, lower jaw bearing a functional edge consisting of 48–53 teeth whose oblique cusps virtually overlap to form a continuous cutting edge, gill slits small, pectoral fins paddlelike, two spineless dorsal fins about equal size, anal fin lacking, caudal keels present, caudal fin semilunate and appearing powerful. Body brownish, purplish, or bluish gray, sometimes mottled by irregular spots, ventral surface minimally lighter than dorsum.

distribution

Polar and temperate seas, from high latitudes well above the Arctic Circle in waters adjoining the Atlantic Ocean to at least as far south in the Atlantic Ocean as 32°N on the Blake Ridge, approximately 230 mi (370 km) off the coast of Savannah, Georgia, United States. Most common north of Cape Cod, United States, in the western Atlantic and north of Great Britain in the eastern Atlantic. There are no incontrovertible records of Greenland sharks from the Southern Hemisphere or from the Pacific or Indian Oceans, although other sleeper sharks of the genus do inhabit those waters.

habitat

The only well-documented sharks to inhabit the Arctic, common in waters below 32°F (0°C) that are seasonally covered by sea ice. In northern portions of the range these sharks can be found lurking below landfast ice, or in open water at depths exceeding 500 ft (152 m), or in knee-deep shallows. At more southerly latitudes, they are usually only seen during the winter. However, this species probably goes unnoticed, residing year-round in cold, deep waters, where it has been seen at depths as great as 7,218 ft (2,200 m). These sharks may occasionally inhabit brackish waters, as indicated by reliable reports of individuals captured over 50 mi (80 km) upstream in the Saguenay River in Quebec, Canada.

behavior

Somniosus means "sleeper" in Latin, and certainly this shark lives up to its name. Accounts of the lethargic nature of this fish are widespread, including accounts of them being hauled up on hooks with hardly a fight. In describing fresh-caught specimens, Hansen (1963) wrote, "owing to the sluggishness of this fish, it could sometimes be a little difficult to judge if it was dead or alive." How this most sluggish species is capable of catching swift prey such as chars and seals remains a mystery. Although it has never been observed, some Norwegian fisherman believed that a brightly colored parasitic copepod that infects the eyes of many of these sharks might serve as a lure to attract curious prey within striking distance. Nonetheless, those copepods do appear to cause enough damage to the eyes such that one might surmise that this shark does not rely on keen vision to capture its dinner. In some instances sound or olfaction may be the key, and fishing, sealing, and whaling operations have been noted to attract them.

feeding ecology and diet

The examination of stomach contents and studies of stable isotopes indicate that these sharks feed at a number of trophic levels, and while they can swallow smaller prey whole, they also feed in a piecemeal fashion by scooping large, melon ball–like chunks from larger items. Their diet has included jellyfishes, brittle stars, sea urchins, amphipods, crabs, snails, squids, and seabirds; a variety of fishes such as small sharks, skates, herrings, chars, salmons, eels, capelins, redfishes, sculpins, lumpfishes, cods, haddock, wolfishes, and halibuts; as well as marine mammals such as seals and narwhals. As well as preying on live organisms, these sharks are well known to gluttonously consume animals compromised by fishing gear, along with almost any carrion. The latter habit prompted whalers to give them the unflattering name of gurry or "garbage" sharks. In some areas the flesh is toxic to both humans and dogs, and must be properly prepared before consumption. In addition, the flesh of some sharks is heavily contaminated with persistent organic pollutants that probably enter the sharks via their diet. Although this species will eat others of its kind that are compromised by fishing gear, it is not known whether it is normally preyed upon by species other than humans. Limited growth data on these sharks suggests they grow slowly and that some individuals may live for over 100 years.

reproductive biology

Little is known about the reproductive biology of this species; but presumably fertilization is internal and development is ovoviviparous. Information regarding age at first maturity, gestation period, numbers of embryos per litter, and size at birth are nonexistent, except for some information from a single report of a 16 ft (5 m) long female that contained 10 embryos. The pups appeared full term and the single embryo measured was about 14 in (36.7 cm) long. Based on maximum size, males probably mature at a smaller size than females. Given the great size of this species and the tendency for it to eat anything in its path, it is possible that shallow nursery areas segregate neonates and juveniles from adults.

conservation status

Not threatened.

significance to humans

Regardless of its large size, this species is inoffensive to humans, and no authenticated attacks have been reported. This fish has been employed in various ways by Inuit communities; the flesh consumed by humans and sledge dogs, the liver providing a fine oil, the teeth and rough skin used for cutting and scraping. Europeans, Greenlanders, and Icelanders have also fished the species for similar purposes. Directed commercial fisheries existed from about the mid-1800s until about the mid-1900s. Other than relatively small numbers taken by some traditionalists, most captured today are probably taken as bycatch in fisheries directed at other fishes such as turbots. In some areas these sharks have been so numerous and destructive to fishery equipment and operations that they have been looked upon as a nuisance and were sometimes targeted by operations aimed at reducing their abundance.

Piked dogfish

Squalus acanthias

family

Squalidae

taxonomy

Squalus acanthias Linnaeus, 1758, European sea ("Oceano europaeo").

other common names

English: Grayfish, spiny dogfish, spurdog; white-spotted spurdog; French: Aiguillat commun; German: Gemeiner dornhai; Spanish: Mielga; Danish: Pighai; Dutch: Dornhaai; Norwegian: Pighaa.

physical characteristics

A small shark; total length of females 4 ft (120 cm), weight up to 21.6 lb (9.8 kg); total length of males 3 ft (160 cm). Body quintessentially sharklike, snout narrow, eyes large, spiracles present, mouth with similarly shaped teeth in top and bottom jaws, 28 teeth in top jaw and 22–24 teeth in bottom jaw, first and second dorsal fins each bearing a dorsal spine, second dorsal spine more pronounced than first, anal fin lacking, caudal keels present, caudal fin without subterminal notch on upper lobe. Dorsal surface of body usually slate-colored, flanks each with a row of small white spots that are most conspicuous on younger fish, ventral surface light gray to white.

distribution

Antitropical marine and estuarine waters throughout the Atlantic and Pacific Oceans and adjoining seas, encompassing boreal to warm-temperate waters in the Northern Hemisphere and antiboreal to warm-temperate regions in the Southern Hemisphere.

habitat

Inhabits inshore and offshore waters associated with continental and insular shelves. Given its migratory nature and widespread abundance, this small dogfish utilizes a broad scope of habitats. Can be found as in waters as shallow as the intertidal zone, although may venture as deep and probably deeper than 2,952 ft (900 m). Seem to prefer waters about 42–46°F (6–8°C); however, tolerates up to 59°F (15°C). May make short upstream incursions utilizing the saltwater wedges of tidal rivers.

behavior

Although they cannot be characterized as being swift, these sharks are strong swimmers and can maintain a steady cruising pace. Gregarious fishes, they typically gather and migrate in large schools consisting of equally sized individuals. Schools of large adult females tend to be more common inshore; schools of juveniles are more common offshore. In the northwestern Atlantic Ocean, their north-south seasonal migration usually places them in the northernmost part of their range near Labrador by early fall, and in the southernmost part of their range off the Carolinas to northeastern Florida by midwinter. In addition to these seasonal movements, they also exhibit general movements inshore during warmer months and movements offshore as it gets colder. Tagging studies have shown that some journey over long distances, with certain transoceanic wanderings in the North Atlantic and North Pacific Oceans totaling 994–4,039 mi (1,600–6,500 km).

feeding ecology and diet

Typically feeds in packs, often moves into an area and lays waste to or drives off most fishes. In any wide portion of their range, fishes usually constitute the largest percentage of the diet, followed by squids and other invertebrates. A list of stomach contents would mimic a relatively thorough inhabitant list for many waters. In the northwestern Atlantic Ocean, small schooling fishes such as herrings, menhadens, capelins, sand lances, and mackerels offer them ample opportunity to gorge. Although their relatively small size limits their lethal abilities, fishes as large as cods and haddocks can fall prey to these ravenous squaliforms. Because of their vast appetites, these fishes can grow about 0.6–1.4 in per year (1.5–3.5 cm), and estimates of their longevity based on the interpretation of growth rings on their spines are commonly about 40 years, but may be as long as 100 years. Because of their relatively small size, they are preyed upon by large sharks and teleosts, seals, killer whales, and of course, humans.

reproductive biology

More is known about the reproductive biology of this fish than about that of any other shark, skate, or ray. Males reach maturity at about 11 years old, females at 18–21 years. Fertilization is internal, development is ovoviviparous, and gestation may last from 18–24 months. Litter size ranges from 1–15 pups; however, six or seven is typical. At birth the neonates are usually about 10 in (26 cm) long.

conservation status

Considered to be overexploited in many regions and listed by the IUCN as Lower Risk/Near Threatened. However, in many parts of its range, this is probably the most abundant shark, and can be so common that within the Gulf of Maine, to "mention all the localities from which they have been reported would be simply to list every seaside village and fishing ground from Cape Cod to Cape Sable" (Bigelow and Schroeder, 1953).

significance to humans

Almost anyone who has taken an advanced course in biology has toiled to locate the cranial nerves of these fishes. Their flesh has been eaten fried (as in "fish and chips"), broiled, and baked by humans, and ground into meal for pet food. They have also been the bane of many commercial fisheries for driving valuable catches away, beating other fishes to the bait, and ruining nets full of keepers. Furthermore, they can administer a merciless sting with their sharp spines.

Resources

Books

Bigelow, H. B., and W. C. Schroeder. "Sharks." In Fishes of the Western North Atlantic: Lancelets, Cyclostomes, and Sharks. Sears Foundation for Marine Research Memoir no. 1, pt. 1, edited by J. Tee-Van, C. M. Breeder, S. F. Hildebrand, A.E. Parr, and W. C. Schroeder. New Haven: Yale University Press, 1948.

——. Fishes of the Gulf of Maine. Fishery Bulletin 74. Washington, DC: U.S. Fish and Wildlife Service, 1953.

Burgess, G. H. "Spiny Dogfishes: Family Squalidae." In Bigelow and Schroeder's Fishes of the Gulf of Maine, edited by B. B. Collette and G. Klein-MacPhee. Washington, DC: Smithsonian Institution Press, 2002.

Castro, J., and R. L. Brudek. "A Preliminary Evaluation of the Status of Shark Species." In Fisheries Technical Paper 380. Rome: Food and Agriculture Organization of the United Nations, 1999.

Compagno, L. J. V. "Sharks of the World: Part 1: Hexanchiformes to Lamniformes." FAO Fisheries Synopsis 125, vol. 4, pt. 1. Rome: Food and Agriculture Organization of the United Nations, 1984.

——. "Systematics and Body Form." In Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes, edited by W. C. Hamlett. Baltimore, MD: Johns Hopkins University Press, 1999.

——. "Checklist of Living Elasmobranchs." In Sharks, Skates, and Rays: The Biology of Elasmobranch Fishes, edited by W. C. Hamlett. Baltimore: Johns Hopkins University Press, 1999.

de Carvalho, M. R. "Higher-Level Elasmobranch Phylogeny, Basal Squaleans, and Paraphyly." In Interrelationships of Fishes, edited by M. L. J. Stiassny, L. R. Parenti, and G. D. Johnson. San Diego: Academic Press, 1996.

Last, P. R., and J. D. Stevens. Sharks and Rays of Australia. Melbourne, Australia: CSIRO Division of Fisheries, 1994.

Shirai, S. "Phylogenetic Interrelationships of Neoselachians (Chondrichthyes: Euselachii)." In Interrelationships of Fishes, edited by M. L. J. Stiassny, L. R. Parenti, and G. D. Johnson. San Diego: Academic Press, 1996.

Periodicals

Beck, B., and A. W. Mansfield. "Observations on the Greenland Shark, Somniosus microcephalus, in Northern Baffin Island." Journal of the Fisheries Research Board of Canada 26 (1969): 143–145.

Berland, B. "Copepod Ommatokoita elongata (Grant) in the Eyes of the Greenland Shark: A Possible Cause of Mutual Dependence." Nature 191 (1961): 829–830.

Borucinska, J. D., G. W. Benz, and H. E. Whiteley. "Ocular Lesions Associated with Attachment of the Parasitic Copepod Ommatokoita elongata (Grant) to Corneas of Greenland Sharks, Somniosus microcephalus (Bloch & Schneider)." Journal of Fish Diseases 21 (1998): 415–422.

Caloyianis, N. "Greenland Sharks." National Geographic 194, no. 3 (1998): 60–71.

Drainville, G., and L. Brassard. "Le requin Somniosus microcephalus dans la Rivière Saguenay." Le Naturaliste Canadien 87 (1960): 269–277.

Fisk, A. T., S. A. Tittlemier, J. L. Pranschke, and R. J. Norstrom. "Using Anthropogenic Contaminants and Stable Isotopes to Assess the Feeding Ecology of Greenland Sharks." Ecology 83 (2002): 2,162–2,172.

Francis, M. P., J. D. Stevens, and P. R. Last. "New Records of Somniosus (Elasmobranchii: Squalidae) from Australia, with Comments on the Taxonomy of the Genus." New Zealand Journal of Marine and Freshwater Research 22 (1988): 401–409.

Hansen, P. M. "Tagging Experiments with the Greenland Shark (Somniosus microcephalus Bloch and Schneider) in Subarea 1." Special Publication, International Commission of Northwest Atlantic Fisheries 4 (1963): 172–175.

Herdendorf, C. E., and T. M. Berra. "A Greenland Shark from the Wreck of the SS Central America at 2,200 Meters." Transactions of the American Fisheries Society 124 (1995): 950–953.

Jahn, A. E., and R. L. Haedrich. "Notes on the Pelagic Squaloid Shark Isistius brasiliensis." Biological Oceanography 5(1987): 297–309.

Johnson, C. S. "Sea Creatures and the Problem of Equipment Damage." U.S. Naval Institute Proceedings 1978 (August 1978): 106–107.

Koefoed, E. "A Uterine Foetus and the Uterus from a Greenland Shark." Fiskeridirektoratets Skrifter, Serie Havundersøkelser 11, no. 10 (1957): 8–12.

Nakano, H., and M. Tabuchi. "Occurrence of the Cookiecutter Shark, Isistius brasiliensis, in Surface Waters of the North Pacific Ocean." Japanese Journal of Ichthyology 37 (1990): 60–63.

Widder, E. A. "A Predatory Use of Counterillumination by the Squaloid Shark, Isistius brasiliensis." Environmental Biology of Fishes 53 (1998): 267–273.

George W. Benz, PhD