They are found in areas from the tropics to the icy waters of the Arctic
and the Antarctic. The family contains both benthic and pelagic species
which range in size from approximately 40cm to over 6m in length.
General body shape - They generally have broad heads with short, flattish snouts. The mouth is positioned on the underside of the head. Some sleeper sharks are bioluminescent.
Eyes - Many of these sharks dwell at depths where there is little or no light, so they don't rely heavily on their vision. This is a good thing as some of them, such as the Greenland shark, are prone to a copepod parasite called Ommatokoita elongata which attaches itself to the cornea and can cause impaired vision or even blindness.
Teeth - The upper teeth are small and needle-like while the lower teeth are broader and flatter.
Gills - Five pairs of gill slits and large spiracles.
Fins - Both the first and second dorsal fin are low and quite small relative to the shark's body. Fin spines are present on both dorsal fins of all genera except Scymnodalatias and Somnosius.
No anal fin present. Relatively small pectoral and pelvic fins. Caudal fin heterocercal with the upper lobe being longer than the lower lobe.
These sharks are often considered to be slow and sluggish though research suggests that sharks such as the Greenland are formidable predators and can catch large, fast moving prey such as sea birds and seals.
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