SCIENCE

Genetic research helps uncover the Atlantic sixgill shark. (National Geographic)

Are there any shark sanctuaries in the species range of the newly identified species? Use today’s MapMaker Interactive map to find out.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit, including a link to today’s MapMaker Interactive map.

Discussion Ideas

• So, tell us about the species of shark described in the new research.
  • The Atlantic sixgill shark (Hexanchus vitulus) lives in the deep, cold water of the tropical Atlantic Ocean. Individuals were studied around Belize, the Gulf of Mexico, and Bahamas.
  • Atlantic sixgill sharks are closely related to the two other sixgill species: bigeye sixgills and bluntnose sixgills. All sixgill species are most closely related to sevengill sharks and dogfish sharks. Sixgill sharks are sometimes called cow sharks or mud sharks.
    • As their name implies, sixgill sharks have six pairs of gill slits on either side of their head. (Most sharks have five; sevengills have … guess how many.)
    • Sixgills are among the most “primitive” of shark species, meaning their anatomy resembles fossils of shark ancestors.
    • Sixgills have unusual teeth. Teeth in their upper jaw are sharp, familiar points. (Like these.) Teeth in their lower jaw, however, are weird comb-like or saw-like plates. (Like these.)
    • Sixgills are ovoviviparous, meaning they do not lay eggs, like most fishes. Instead, mother sharks give birth to live pups—sometimes 100 at a time!

• How was the new species of sixgill discovered?
  • genetics. Researchers “analyzed 1,310 base pairs of two mitochondrial genes to see if there were enough molecular differences between samples.”
    • The discovery was not an entire surprise. Researchers had long suspected the Atlantic population of the bigeye sixgill was a separate species. The scientific name (Hexanchus vitulus) was first proposed in 1969.

• How do Atlantic sixgill sharks differ from their bigeye and bluntnose cousins?
  • genetics. The fish look and behave almost identically. The Atlantic sixgill was “hiding in plain sight” until researchers analyzed its DNA.
  • size. Atlantic sixgills are about 1.8 meters (6 feet) long, while their cousins can be nearly three times that length.
  • species range. Atlantic sixgills live in the tropical Atlantic, while their bigeye cousins mostly inhabit the tropical Pacific and Indian oceans.

TEACHERS TOOLKIT

Nat Geo: New Species of Shark Discovered in Deep Sea

Nat Geo: Shark Sanctuaries

(extra credit!) Marine Biodiversity: Resurrection of the sixgill shark Hexanchus vitulus Springer & Waller, 1969 (Hexanchiformes, Hexanchidae), with comments on its distribution in the northwest Atlantic Ocean