Squaliformes

## Defining Features

Commonly known as the "sleeper" or "dogfish" sharks, Squaliformes is a part of the Elasmobranchii class that is characterized by an absence of the anal fin. Sleeper sharks typically have two dorsal fins and five pairs of gill slits as well as large, almond-shaped eyes. They may have spines along one or both of their dorsal fins and many species are bioluminescent. They also have large, conspicuous spiracles above and behind each eye. The jaws in many species have strong cutting teeth in short mouths and Squaliformes reproduce through ovoviviparity. They also do not have a nictating membrane.

## Habitat and Range

Dogfishes are generally bottom-dwelling, and reside in the deep ocean, reaching depths as far as 20,000 feet. As a result, they are not commonly encountered by divers, and not extensively studied. They can be found everywhere in the ocean, although many species reside around temperate or tropical latitudes and inhabit nearshore waters associated with continental insular shelves and slopes.

## Fisheries Conservation and Concern

Squaliformes sharks are often hunted by humans for medicinal purposes as well as for food. However, research surrounding the human impact on these populations still remain scarce as they reside in deep waters and are not often subject to study.

## Closest Relatives

Echinorhiniformes, Pristiophoriformes, Squantiniformes, Hexanchiformes

## Example Species in Squaliformes

### Greenland Shark

#### *Somniosus microcephalus*

Defining Features: The Greenland shark is a member of the sleeper shark family known as the Somniosidae. It is also the longest living known vertebrate. It's coloration ranges from grey to brown, and it's characterized by a round snout and small fins compared to it's body size. Radio carbon dating of isotopes within the shark eye lens estimate that the creature can live up to 500 years. It can grow up to a length of 7 meters.

Range & Habitat: Greenland sharks prefer colder, deeper climates, and they can be found anywhere from the surface to as far as 2000 meters in depth. They reside in the Arctic and North Atlantic oceans. These sleeper sharks are slow moving, swimming at rates less than 3 km an hour.

IUCN Concern: The Greenland shark is considered a near threatened species by the IUCN. They are hunted for their liver oil, as one large specimen can produce up to 30 gallons.

### Portuguese Shark

#### *Centroscymnus coelolepis*

Defining Features: Portuguese Sharks are defined by their stout bodies and two small dorsal fins. In their jaws they have an upper set of teeth that are long and pointed and a lower set that are short and broad. As juveniles Portuguese sharks are dark blue, as they grow they will turn black, and then brown when the reach maturity. As with all other Squaliformes they have no anal fin.

Range & Habitat: The Portuguese shark covers many areas including the North Atlantic Ocean, the Western Mediterranean Sea, and some areas of the Western Pacific Ocean. They live in areas of great depths going from 3000 to nearly 9000 feet deep. They typically are found in cold water with a temperature around 5-6 degrees Celsius.

IUCN Concern: Near Threatened

## Example Species in the Gulf of Maine

### Spiny Dogfish

#### *Squalus acanthias*

Defining Features: The spiny dogfish, also commonly known as the "Cape Dogfish," or "Springfish," resides around the Gulf of Maine. Spiny Dogfish are slim, they have a narrow, pointed snouts, and characteristic white spots along their body. They have two dorsal fins, along with two, ungrooved spines. Males can grow up to 3.3 feet, while females grow to about 4 feet.

Range & Habitat: The spiny dogfish can be found in the North Atlantic and the North Pacific Oceans, in temperate and subarctic areas. In the Northwest Atlantic areas, they are found from Labrador to Florida and most abundant in Nova Scotia and Cape Hatteras.

IUCN Concern: Spiny dogfish are not over-fished and not subject to over-fishing.

## References

Fish Base: https://www.fishbase.in/summary/OrdersSummary.php?order=Squaliformes

Elasmo-Research: http://www.elasmo-research.org/education/ecology/id-squaliformes.htm

Britannica: https://www.britannica.com/animal/Greenland-shark

NOAA Fisheries: https://www.fisheries.noaa.gov/species/atlantic-spiny-dogfish

Shark Insider: https://www.sharksider.com/portuguese-dogfish-shark/