Squalomorphii is a superorder of cartilaginous fishes, generally characterized by lacking traits such as an anal fin, nictitating membrane, or suborbital shelves in the cranium. Also called squalea, or squalean sharks. There are about 163 living

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

in 11

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

. Squalean sharks are divided into four orders: the

Hexanchiformes The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seven extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens. Hexanchif ...

, Squaliformes, Squatiniformes, and Pristiophoriformes.

Classification

Order Hexanchiformes

The order Hexanchiformes is a very small and primitive order consisting of cow sharks and frilled sharks. These sharks have only 1 dorsal fin, 6-7 gill slits, and no nictitating membrane on the eyes. Cow sharks are fairly large and stocky, while frilled sharks are smaller and have eel-like bodies. The oldest fossils from this order can be dated back to the mid-

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

. There are six living species in 4 genera, and 2 families. * Family Hexanchidae (Cow sharks) * Family Chlamydoselachidae (Frilled sharks)

Order Squaliformes

The order Squaliformes is a large, ancient order of sharks. Sharks from this order have two dorsal fins -usually with spines-, no anal fin, and no nictitating membrane on the eyes. Squaliform sharks are extremely variable in size and shape, and can be found in most marine habitats throughout the world. Like Hexanchiformes, members of Squaliformes can be found as early as the Jurassic period. There are around 126 species in 23 genera, and 7 families. * Family Centrophoridae (Gulper sharks) * Family

Dalatiidae The Dalatiidae are the family of kitefin sharks of the order Squaliformes (the term "kitefin shark" also refers specifically to the species '' Dalatias licha''). Members of this family are small, under long, and are found worldwide. They have ci ...

(Kitefin sharks) * Family

Echinorhinidae ''Echinorhinus'' is the only extant genus in the family Echinorhinidae. Taxonomy Echinorhinidae are traditionally classified in the order Squaliformes, together with kitefin and gulper sharks.Compagno, 2005. "Sharks of the World". However, a ...

(Bramble sharks) * Family

Etmopteridae The Etmopteridae are a family of sharks in the order Squaliformes, commonly known as lantern sharks. Their name comes from the presence of light-producing photophore A photophore is a glandular organ that appears as luminous spots on vari ...

(Lantern sharks) * Family Oxynotidae (Rough sharks) * Family

Somniosidae The Somniosidae are a family of sharks in the order Squaliformes, commonly known as sleeper sharks. The common name ''"sleeper shark"'' comes from their slow swimming, low activity level, and perceived non-aggressive nature. Distribution and ha ...

(Sleeper sharks) * Family Squalidae (Dogfish sharks)

Order Squatiniformes

The order Squatiniformes is a small order of highly specialized and recognizable sharks called angel sharks. The angel sharks have flattened bodies and broad pectoral fins, as well as camouflaged coloration. These characteristics allow angel sharks to blend in with their benthic environments. Members of Squatiniformes have been found since the late Jurassic period. There are 23 species in 1 genus, and 1 family. * Family Squatinidae (Angel sharks)

Order Pristiophoriformes

The order Pristiophoriformes is a small order of unique sharks called sawsharks. Sawsharks have a long snout covered in teeth, between 5-6 gill slits, and no anal fin. They also have a pair of barbels usually located halfway down the snout. Sawsharks are frequently confused with sawfish, which are members of the ray order Pristiformes. Sawsharks can be discerned from sawfish thanks to their

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

gill slits, which differ from the sawfish's

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

gill slits. These sharks can mostly be found in deep benthic environments. Fossils of members of this order have been found since the late Jurassic period.Froese, Rainer, and Daniel Pauly, eds. (2013). "Pristiophoridae" in FishBase. October 2013 version. There are 8 species in 2 genera, and 1 family. * Family Pristiophoridae (Saw sharks)

Classification

Order Hexanchiformes

Order Squaliformes

Order Squatiniformes

Order Pristiophoriformes

References

Further reading