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Monsters in a barrel, sea slugs and the art of (man-o) war

The views expressed are those of the author and are not necessarily those of Scientific American.


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Still from Coral Morphologic's film 'Man O War'

Because I’ll never grow tired of seeing incredible footage of sea creatures, here are a few of the best ones I’ve seen lately.

First up, a video by a group called Coral Morphologic, which is an art-science project led by James Cook University-educated marine biologist Colin Foord, and American musician Jared McKay. “With the aquarium as our primary medium, we explore the artistic possibilities of living coral reef organisms via HD videography and site-specific artworks,” Foord and McKay say on their website, which features videos of anemone birth, a coral nursery and the tiny heart urchin pea crab. The video below, which was a special installment of their Natural History film series last year, celebrates the gorgeous, loopy tendrils of the Portuguese man-o-war (Physalia physalis) that tumble like curled ribbons from an obscured, gas-filled bladder.

‘Man O War’ from CORAL MORPHOLOGIC on Vimeo.

Unlike jellyfish, the Portuguese man-o-war is not a single organism, but a colony of four different kinds of smaller animals, called polyps and medusae, that have highly specialised body types to allow for very different functions. The gas-filled bladder, otherwise known as the pneumatophore or sail, is one, and its function is to keep the colony together. Then there’s the dactylozooids, or tentacles, which are responsible for finding and capturing food using cnidocytes, or stinging cells. The gastrozooids are the feeding and digesting organisms, while the gonozooids are in charge of producing gametes for reproduction.

The first recorded human death by man-o-war occurred in 1987, when a 67-year-old woman was swimming at Riviera Beach in Florida. Before this, researchers had thought that as much as 15 m of tentacular contact was needed to kill a human, but the team reporting on the death in Annals of Emergency Medicine estimated from the woman’s sting marks that she had only touched between 3 and 6 metres-worth of tentacles. At the time of reporting, a young boy had died in Australian waters having been exposed to just 1.5 m of tentacles. The researchers suggested that despite the fact that the victims only had stings on relatively small areas of their bodies, both deaths occured at a time of year when man-o-wars reach full maturity, so these indivisuals were likely at their most robust and venomous.

Phronima – Monsters in Barrels from Parafilms on Vimeo.

Rumoured to be the inspiration for Alien’s queen alien morph, Phronima sedentaria is a tiny and translucent deep-sea predator that feeds off gelatinous animals and lives inside their corpses. Found all over the world in temperate, subtropical and tropical waters, the female Phronima can grow up to 42 mm long, while the males only reach around 15 mm long.

The females will capture prey such as siphonophores (a group that includes corals and jellyfish) and barrel-shaped, planktonic tunicates called salps and cut into them using their sharp claws. According to a 1988 paper published in Journal of Crustacean Biology by Carol E. Diebe from the Museum of New Zealand Te Papa Tongarewa, one particular female she observed, “entered the salp, cut out the brain and gill bar, and consumed them, ate the stomach and its contents, and then remained relatively quiescent for approximately five hours. The female then resumed eating the salp, cutting off strips of tissue at both ends, and removing pieces of the internal organs, eating only the muscle bands”.

At this point, she will continue manipulating the gelatinous remains of the salp into a barrel shape by scraping the walls smooth over many hours. Once the barrel is complete, the female will use her new gelatinous home to propel herself through the ocean in search of more food. She will lay her eggs inside the barrel, and raise and feed her progeny there until they’re old enough to leave. Rather fittingly, the Greek origin of the word ‘Phronima’ means “clever”

‘The Lettuce Slug’ from CORAL MORPHOLOGIC on Vimeo.

Another of the Coral Morphologic videos, this one shows the super-strange lettuce sea slug (Elysia crispata),  which performs a process known as kleptoplasty to stay alive. This involves eating the cell sap of algae, and instead of digesting all of it, will funnel some of it, including the chloroplasts that algae use to conduct photosynthesis, through specialised passages in the digestive tract. They are then stored in appendages called parapodia, and here they will remain for up to four months and undergo photosynthesis to provide the sea slug with extra energy at times when food is scarce.

And finally, the real-life Pokemons, Glaucus atlanticus and Glaucus marginatus, commonly known as blue dragons. With very few relatives to speak of, these sea slugs are the only two species that belong the family Glaucidae. They mostly float upside-down on the surface of the ocean, sucking in air and storing it in their stomachs for bouyancy. Unlikely predators of the Portuguese man-o-war, blue dragons are immune to its toxins, and this allows them to eat everything, including the tentacles. They can then store the toxins in sacs on their cerata, which are those finger-like projections, so they can inflict nasty stings to their own would-be predators later on.

The main differences between these two species are that G. marginata has more cerata than G. atlanticus, but G. atlanticus has a much longer tail, or metapodium. And growing to 3 cm in length, G altanticus is much larger than G. marginata, which only stretches up to 12 mm in length.

Pre-order my new book, Zombie Tits, Astronaut Fish and Other Weird Animals (due for release next month), here.

Bec Crew About the Author: Bec Crew is a Sydney-based science writer and award-winning blogger. She is the author of 'Zombie Tits, Astronaut Fish and Other Weird Animals' (NewSouth Press). Follow on Twitter @BecCrew.

The views expressed are those of the author and are not necessarily those of Scientific American.





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