Discover Diving
  • Home
    • Snorkel Safaris
    • Beach Ranger
  • Dive training
    • Getting started
    • More Scuba Training
    • Technical diving
    • Snorkel training
  • First Aid Training
  • Dive Charters
    • Booking with us
    • Dive sites
    • Accommodation
  • Services
    • COVID CPAP
    • Air and gas fills
    • Kit hire
    • Regulator servicing
    • Dry suit repairs
    • Cylinder testing
  • Shop
    • Online shop
  • Our Club
    • DIve planning
    • Snorkel Club >
      • Pool party 2019
    • Searchmembers
  • What's happening
    • SPLASH IN
    • Newsletters
    • Dive blog
    • Out and about
  • Contact

Michelle's blog

What are cuttlebones for?

21/11/2021

0 Comments

 
​As I child I had a budgerigar called Dinsdale. Dinsdale was a pretty happy bird who would cheerfully run round my desk, leaving special presents on my homework (!) and hop back into his cage on command. He loved hitting the bell that was attached to a little round mirror and pecking hard at his cuttlefish.  Of course, he didn’t really have a whole cuttlefish in the cage with him, just the hard, bony bit.

Cuttlefish bones aren’t actually bones at all, they are a special kind of shell.  And while we are at it, cuttlefish aren’t fish either. Cuttlefish are one of the Cephalopods and they have their own family name Sepiidae. The early ancestors had a shell for protection and existed before the first fish had evolved. Modern cuttlefish don’t have an external shell but rely on camouflage for evading predators. 

The common cuttlefish (Sepia officinalis) also produces a brown ink, which can be harvested from their ink sacs.  Most of us would recognise the colour of the ink from old fashioned brown sepia photos, and that’s how the ink got its name. The chemistry and biosynthesis of ink in cephalopods is fairly complex. It is a form of the common biological pigment melanin which is the same molecule responsible for your skin developing a tan after exposure to sunlight. Who’d have thought you and the cuttlefish would have so much in common? The eumelanin in the ink sacs is also found in fossils from the early Jurassic period around 200 million years ago.

For a soft bodied animal, it seems strange that there should be a good fossil record. The cuttlebone is generally well preserved. When the cuttlefish are alive the cuttlebone is a mix of chitin (a really large structural sugar molecule) and aragonite (one of the three forms of calcium carbonate). After the animal dies, the chitin will break down fairly readily but the aragonite persists. That means that it is possible to find fossilised remains of cuttlefish that are readily identifiable and from modern catches of cuttlefish, your budgie gets a calcium supplement.

The cuttlebone has a very specific function in the cuttlefish. It’s clearly not for defence – what use would an internal bone be? Cuttlefish have a short life span, maybe only 1-2 years and during that time they have a phenomenal growth rate (up to 10 kg) so for a cuttlefish conserving energy is critically important. The cuttlebone structure is full of holes and the cuttlefish can control liquid or gas into those spaces to effortlessly control its buoyancy.

The cuttlebone is a long oval structure made of around 100 chambers, with the chamber lying at the head end being the oldest, other layers are added as the cuttlefish grows. Lying along the cuttlebone is the siphuncle, which is a strand of tissue that connects all the small chambers.  In order to add water to the cuttlebone, the cuttlefish makes the blood in the siphuncle more salty by pumping salt out of the chamber. Water in the chamber is drawn out of the chamber and into the blood by osmosis and oxygen and carbon dioxide come out of solution and make up the volume in the chamber by diffusing from the siphuncle.  So it’s not true to say the siphuncle pumps the water….more that it pumps the salt and that causes the water to be drawn out. Siphuncles rarely get preserved in fossil records but you can usually see the notches in the cuttlebone where the siphuncle used to be.
​
Removing water from the chambers of the cuttlebone reduces the overall density and causes the cuttlebone to float. Cuttlefish aim to maintain neutral buoyancy and will swim up or down with the minimum of effort. In addition to this, the cuttlefish can control whether the chambers towards the head or the tail end are water filled or gas filled, making it’s journey from depth towards the surface even easier as it adjusts its trim. Next time you’re diving, be more cuttlefish, perfect buoyancy and perfect trim.
 

0 Comments



Leave a Reply.

    Author

    Michelle has been scuba diving for nearly 30 years. Drawing on her science background she tackles some bits of marine science. and sometimes has a sideways glance at the people and events that she encounters in the diving world.

    If you have a marine science question that's been bugging you, please get in touch.

    Categories

    All
    Basking Sharks
    Biosphere
    Dive Boat
    Dive Buddy
    Dive Centre
    Dive Equipment
    Dive Instructor
    Dive Training
    Drysuit
    Isle Of Man
    Marine Exploration
    Marine Life
    Media
    Safety
    Science
    Scuba Diving
    Snorkelling
    Winter Diving
    Wreck

    RSS Feed

    Archives

    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    April 2019
    September 2017
    August 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016

Come and discover diving in the Isle of Man!


Hours

Opening Hours
From 1/9/22 onwards:
Saturday 9-5
Sunday 9-4
​

Telephone

+44 (0)1624 833008

Email

info@discoverdiving.im
  • Home
    • Snorkel Safaris
    • Beach Ranger
  • Dive training
    • Getting started
    • More Scuba Training
    • Technical diving
    • Snorkel training
  • First Aid Training
  • Dive Charters
    • Booking with us
    • Dive sites
    • Accommodation
  • Services
    • COVID CPAP
    • Air and gas fills
    • Kit hire
    • Regulator servicing
    • Dry suit repairs
    • Cylinder testing
  • Shop
    • Online shop
  • Our Club
    • DIve planning
    • Snorkel Club >
      • Pool party 2019
    • Searchmembers
  • What's happening
    • SPLASH IN
    • Newsletters
    • Dive blog
    • Out and about
  • Contact