Ghost catsharks

When ghost catsharks are born, the embryos have two rows of large tooth-like denticles on their back, which the scientists believe they use to hatch themselves out of the egg capsule.

Apristurus are a deepwater genus of the catshark family, or Scyliorhinidae.  This single genus of shark represents many different species living in deepwaters (>500 m) across the globe.  They are problematic to scientists because the different species look so similar that they are extremely difficult to tell apart.  Dr. Kazuhiro Nakaya, from Hokkaido University in Japan, is one of the few people in the world who can do just that. 

Dr. Nakaya is working on a worldwide revision of the genus Apristurus, and when he is done hopes to have a more complete view of what species comprise the group, and where they are found geographically.  For Dr. Nakaya, who has examined specimens on both sides of the north Atlantic, MAR-ECO represents a unique opportunity to examine specimens that bridge the gap between these waters, and may help to complete our understanding of their distribution. 

In addition, his work will allow other marine scientists to tell these species apart through the use of key characters.  These key characters, obvious on some marine organisms, are often quite subtle in cat sharks. 

Over many years, through repetitive observations, Dr. Nakaya has mapped out a series of measurements which have significance for this genus.  It is these measurements that allow him to compare one species to another, and ultimately distinguish them.  Once this work is completed and tested, then hundreds of measurements can be reduced to only a few critical ones that alone can tell the species apart.  When these are revealed, other scientists will be able to use them to rapidly identify species.  This in turn can permit other studies in categories such as ecology, population and evolution.

Some facts about the ghost catshark, Apristurus manis:

  • Ghost catsharks lay eggs
  • They have an organ called a shell gland, which produces a capsule for the embryo (see photo of egg capsule)
  • Embryos, when born, have two rows of large tooth-like denticles on their back, believed to aid in the hatching process (see photo)
  • Ghost catsharks, like other deepwater shark species, have enormous livers that partially function as a buoyancy device, allowing the animal to suspend itself in the water column
  • Ghost catsharks seem to have two distinct color phases, dark brown and tan
  • Ghost catsharks have longer tails than the other catsharks species they share habitat with.  The function of this longer tail is unknown.