Chordata · chordates

Spiny dogfish

Squalus acanthias

Squalidae · spurdogsIUCN: Vulnerable
Spiny dogfish
Photo: Doug Costa, NOAA/SBNMS · Public domain · Wikimedia Commons · resized

A small schooling shark with a spine in front of each dorsal fin, abundant off New England.

Fun factIts pregnancy lasts up to two years, among the longest of any vertebrate.

Waters
Worldwide, Northeast US
Depth zone
Coastal shallows & estuaries, Continental shelf
Diet
Fish, squid & crustaceans
Size
Up to 1.6 m

Classification

Chordata › Chondrichthyes › Squaliformes › Squalidae

  1. Kingdom Animalia animals
    • Many-celled organisms that eat other living things for energy (heterotrophs)
    • Cells have no cell walls
    • Most can move at some stage of life
  2. Clade Bilateria bilateral animals
    • Body has a left and right side that mirror each other (bilateral symmetry)
    • Head end with concentrated nerves; three tissue layers
    • Includes about 99% of all living animal species
  3. Clade Deuterostomia deuterostomes
    • In the embryo, the first opening becomes the anus and the mouth forms second
    • Includes echinoderms and chordates
  4. Phylum Chordata chordates
    • At some stage of life: a stiffening rod along the back (notochord)
    • A hollow nerve cord along the back (dorsal)
    • Slits in the throat (pharyngeal slits) and a tail past the anus
  5. Subphylum Vertebrata vertebrates
    • A skull (cranium) protecting a brain
    • Backbone or similar support around the nerve cord
    • Includes fishes, amphibians, reptiles, birds, and mammals
  6. Infraphylum Gnathostomata jawed vertebrates
    • Jawed vertebrates: jaws formed from gill arches
    • Paired fins or limbs
    • Includes all fishes except hagfish and lampreys, plus all tetrapods
  7. Class Chondrichthyes cartilaginous fishes
    • Skeleton made of cartilage, not bone
    • Skin covered in tooth-like scales (denticles)
    • Teeth constantly replaced; males have claspers for mating
  8. Subclass Elasmobranchii sharks & rays
    • Sharks and rays: five to seven separate gill slits on each side
    • Many rows of replaceable teeth
  9. Clade Selachii sharks
    • Sharks: gill slits on the sides of the head
    • Pectoral fins not joined to the head
  10. Superorder Squalomorphii squalomorph sharks
    • Most have no anal fin; cow and frilled sharks are the exception
    • Includes dogfish, sleeper, and angel sharks
  11. Order Squaliformes dogfish sharks
    • Dogfish sharks: no anal fin
    • Many have spines before the dorsal fins; some glow (bioluminescence)
  12. Family Squalidae spurdogs
    • Spurdogs: a spine in front of each dorsal fin
  13. Genus Squalus
    • Species in the same genus are very close relatives and often look alike.
  14. Species Squalus acanthias Spiny dogfish

Closest relatives in the guide