Image of a Colossal Squid ((Mesonychoteuthis hamiltoni) Image by By © Citron, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=7757015

Dear Readers, if you were asked what the heaviest invertebrate in the world was, you would probably guess (as I did) that it might be some huge beetle, or a massive stick insect. But in fact we would all be out by a factor of about 1,000, because the heaviest invertebrate on earth is in fact the Colossal Squid, which is thought to weight in at about 1,500 lb (700 kilograms), to be between 33 and 46 feet (10 –  14 metres long), and to have the largest eyes of any creature yet discovered – one specimen had eyes that were 16 inches (40 cms) across.

Alas, this creature of the abyssal depths has only previously been seen by humans when dead or dying animals have been found, sometimes when the squid are taking fish from fishing lines and getting themselves entangled. The beaks of the squid were also often found in the stomachs of sperm whale  – they’re thought to make up a large part of the diet of these cetaceans, and the size of the squid was estimated from these indigestible parts. The depth at which the squid swim depends on their age and size, with the largest and oldest squid being found in the bathypelagic zone, 4,000 metres below the surface. No wonder the squid have such huge eyes – it’s dark down there, but it’s thought that the squid can detect such things as the disturbance in photoluminescent plankton caused by either prey fish or predators as they move through clouds of the tiny organisms.

Beak of a Colossal Squid (Photo by By GeSHaFish – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=26210490)

So, you all know that I love cephalopods, and one reason for mentioning the Colossal Squid today is that a juvenile has actually been filmed in the wild for the first time. Not part of a squid. Not a pale and wasted adult at the point of depth. Not a disintegrating corpse. An actual live teenage squid, going about its business unmolested (well, apart from an automatic deep-sea camera of course). I love that we know even less about the depths of the ocean than we do about the surface of the moon.

You can see the Colossal Squid (only 30 cms long!) here. Maybe one day a submersible will see an adult Colossal Squid. Let’s hope it doesn’t end up like the scenes from Jules Verne’s  ‘20,000 Leagues Under the Sea’. In fact, I suspect that the squid would disappear off into the darkness at speed. They are intelligent animals, after all.

Original illustrations from Jules Verne’s ‘20,000 Leagues Under the Sea’ by A. de Neuville and E. Riou [1870], from https://www.researchgate.net/figure/The-original-monster-from-Twenty-thousand-leagues-under-the-sea-Despite-its-name_fig2_267732069