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The glass squid, Cranchia scabra
The Cranchiidae are a family of squid commonly known as “glass squid” which live in oceans around the world. The squid are of no interest to commercial fisheries (yet) and a great deal about this family remains completely unknown. Most of the 60 known species of cranchiidae are small and inconspicuous–indeed the majority are transparent and thus nearly invisible. However the largest known mollusk, the colossal squid (Mesonychoteuthis hamiltoni), is part of the family, (so it might be wise not to antagonize them on the playground).
Glass Squid (Taonius belone) off Hawaii. Photograph by R. Young.
Glass squid are notable for having stubby swollen-looking bodies and short arms except for one long pair of hunting tentacles. The majority of glass squid have bioluminescent organs which they use to hunt, to communicate and to disguise the faint shadows cast by their transparent bodies (predators of the deep can see even the faintest shadows cast by the dim light from the surface). The cranchiid squids themselves sport a variety of interesting and complex eyes which range from giant circular eyes to stalked eyes to telescoping eyes. This little gallery shows how delicate, diverse, and beautiful (and how utterly alien) these squid can be.
Banded Piglet Squid (Helicocranchia pfefferi) photo by keyofv
Bathothauma lyromma (note eyes on stalks!)
A drawing of the piglet squid (Helicocranchia pfefferi)
Sandalops melancholicus by Chun Carl
Teuthowenia megalops
Cranchia scabra
Juvenile cranchiid squid are part of the plankton and live near the surface where they hunt microscopic prey while trying to avoid thousands of sorts of predators. As they mature, they change shape and descend to deeper waters—indeed some species become practically benthic and can be found more than 2 kilometeres under the ocean. Glass squid move up and down the water column by means of a fluid filled chamber which contains an ammonia solution (which maybe explains why they are not on the human menu yet).
Belonella belone
Vitreledonella richardi (photo by Underseahunter Group)
Today we have a special (but largely visual) treat: the pelagic octopus Vitrelladonella richardi. This cephalopod is “transparent, gelatinous, and almost colorless.” Since they are not only transparent but also live in the deeper part of pelagic zone of the ocean (the portion which is near to neither the top nor the bottom) they are rarely seen and little is known about them. The females are ovoviviparous and broods her eggs within her body. Both genders are strongly bioluminescent and use light for hunting, communicating, and hiding (by mimicking the faint light from the surface they can become even more invisible). Even if we don’t know a huge amount about these octopuses, we are privileged to have some amazing photographs of them, thanks to the new generation of submersibles and submersible drones, which are exploring the pelagic regions of the ocean. Look at how exquisite and alien these octopuses appear! It’s hard to believe we share the planet with such strange animals…
Vitreledonella richardi (photo by Underseahunter Group)
Vampyroteuthis infernalis (from http://www.itsnature.org/sea/other/vampire-squid/)
As you probably know, the financial firm Goldman Sachs has been famously compared to a mollusk. During the bleakest depths of the great recession (assuming we are finally past such troubles) Matt Taibbi of Rolling Stone wrote, “The world’s most powerful investment bank is a great vampire squid wrapped around the face of humanity, relentlessly jamming its blood funnel into anything that smells like money.” Naturally, the unbelievably rich bankers were offended and the aggrieved and bombastic spokesman for the bank Lucas Van Praag, hilariously missed the point of the insult by correctly pointing out that vampire squid are actually very small and harmless to humans. Since then, the vampire squid has become the de facto mascot of Goldman Sachs and now represents the bank in political cartoons the same way Uncle Sam appears as the United States or a dragon represents China. The Goldman Sachs squid is usually portrayed as a giant squid dressed up in gothic garb and sporting a vampire’s voracious mien.
Gothic Squid: the reason nobody had a good job for the last three years?
Goldman Sachs indeed deserves such opprobrium for crafting shell-game style derivatives and credit default swaps which helped bring about the recession (while making the bank richer) but what did the actual vampire squid do? The real victim of the quotation was this fascinating oddity of a cephalopod which shares similarities between squids and octopuses and thus merits placement in its own unique taxonomic order, the Vampyromorphida. As Van Praag observed, vampire squid are indeed quite small: they seldom exceed 6 inches (15 cm) with another 6 inches for their tentacles. Although they have eight arms, like octopuses, the creatures additionally possess unique retractile sensory filaments and immense blue-red eyes to help them apprehend their black surroundings. They have two light-sensitive photo-receptors on their head and their bodies are covered with photophores, specialized organs capable of producing light. The photophores at the tips of the arms are larger than the rest and appear as white spots. Vampire squid use these photophores to communicate, to dazzle predators, to hypnotize prey, and to hide themselves by mimicking ambient surface light.
An illustration of the vampire squid by Citron
Vampire squid live in the benthic depths of the ocean 2,000-3,000 feet (600-900 meters) below sea level. They “fly” through their habitat by means of ear-like fins which project from their mantle. To deal with the inhospitable conditions of such depths, they have large gills and hemocyanin-rich blue blood. Much like ground-water dwelling catfish mentioned in a previous post, their velvety/slimy skin is oxygen permeable in order to exploit the precious oxygen to the maximum extent. To quote Wikipedia “The animals have weak musculature but maintain agility and buoyancy with little effort thanks to sophisticated statocysts (balancing organs akin to a human’s inner ear) and ammonium-rich gelatinous tissues closely matching the density of the surrounding seawater.”
Ballooning defensive behavior (photo by R. Flood)
Unlike most cephalopods, Vampire Squid lack ink sacs (which would be of little use in the nearly lightless depths). To make up for the loss, they possess sacs of brightly bioluminescent mucous which they squirt out at predators to dazzle and confuse them. Such a defense costs the squid dear and is only undertaken as a measure of last resort. Additionally when confronted by predators, the vampire squid can inflate its webbing to appear bigger (as in the photo above). The “squids” prey on larval fish, copepods, prawns, cnidarians, and other deep sea arthropods. They are eaten by deep sea fish and by deep diving marine mammals like whales, seals, and sea lions. Little is known of their reproductive cycle although young squid pass through various stages of morphologic form possessing first one set of fins, then two sets of fins, and then one again.
Stauroteuthis syrtensis (photo by David Shale and Claire Nouvian)
One of the reasons I chose mollusks as a topic is to illustrate how diverse life on our own planet is. The mollusks are an insanely heterogeneous phylum of creatures and they have been successful around the globe for the last 540 million years (at least). Even today in the ultracompetitive Holocene world, mollusks thrive just about everywhere. To illustrate this point I am showcasing the enigmatic deep water octopus Stauroteuthis, of which two species are currently known. These octopuses are only found more than 700 meters underwater in the Atlantic Ocean. Although they are most common around 2 kilometers beneath the surface the creatures have been spotted as far as 4 kilometers down. The Stauroteuthids are small benthopelagic octopuses (they are free-swimming but live in close proximity to the ocean floor).
(photo by David Shale)
The Tree of Life Web Project gives us the following overview of Stauroteuthid morphology:
Stauroteuthids are peculiar, gelatinous cirrates with a mantle opening that forms a complete tube around the funnel. They also have peculiar gills and internal shells and a large web that is nearly equally developed between all arms. When observed from submersibles, this octopod commonly has its arms and web formed into a bell-shape (bell-shape posture). Sometimes when the octopod is disturbed, it will inflate the web and draw the arms together at their tips to form a “balloon” with the arms and web (balloon posture). These postures are thought to be involved in feeding and/or defense.
That is nearly all we know about them—it is difficult to study creatures which live 2 kilometers underwater. However I have left out the most exciting fact: the Stauroteuthids are bioluminescent. Certain muscle cells around the suckers have been replaced with photophores which allow the Stauroteuthid octopuses to light up their eight legs like plane runways. The purpose of this luminescence is unknown but it is believed to be for predatory purposes (the lights are thought to direct prey to the octopus’ beak). Possibly the lights also help the octopuses to find and communicate with mates.
Bioluminescent Suckers (photo by ORCA)
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