Squalomorphi is a

superorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

sharks Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

, generally characterized by lacking traits such as an anal fin,

nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. Most ...

, or suborbital shelves in the cranium. Squalomorphs are also called squalea, or squaleans. There are about 163 living

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

in 11

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

. Squalean sharks are divided into six

orders Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * H ...

: Echinorhiniformes,

Hexanchiformes The Hexanchiformes Help:IPA/English, /hɛkˈsæŋkɪfɔːrmiːz/ are a primitive Order (biology), order of sharks, numbering just five extant species in two Family (biology), families, Chlamydoselachidae and Cow shark, Hexanchidae. Chlamydoselach ...

Squaliformes The Squaliformes are an order of sharks that includes about 126 species in seven families. Members of the order have two dorsal fins, which usually possess spines, they usually have a sharp head, no anal fin or nictitating membrane, and fi ...

, Squatiniformes, Pristiophoriformes and the extinct Protospinaciformes.

Extant orders

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

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 Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

. There are six living species in 4

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

, 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 120 species in 22 genera, and 6 families. * Family Centrophoridae (Gulper sharks) * Family Dalatiidae (Kitefin 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 photophores on their bodies. The members of this family are small, under long, and are ...

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

Squalidae Squalidae, more commonly known as dogfish, dog sharks, or spiny dogfish, are one of several families of sharks categorized under Squaliformes, making it the second largest order of sharks, numbering 119 species across 7 families. Having earned ...

(Dogfish sharks)

Order Echinorhiniformes

* Family Echinorhinidae (bramble 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 The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

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 also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

gill slits, which differ from the sawfish's

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. 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)