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Woodblock prints of ages past show giant octopuses ripping apart boats and feasting on sailors like popcorn. These artifacts of ancient sea-lore make for rousing images, but they are quite wrong: octopuses are fierce and cunning hunters but they present little danger to humans—with a noteworthy exception. The truly dangerous octopuses are not giant monsters (perhaps the artists of yesteryear were thinking of the mighty giant squid?) but rather tiny jewel-like beauties from the genus Hapalochlaena which includes only three or four species. Known as blue-ring octopuses the tiny creatures swim in tide pools and shallows of the Indo-Pacific Ocean from Japan down to Australia (where they are most prevalent). Blue-ringed octopuses live on shrimp, crabs, minnows, and horseshoe crabs. They are tremendous hunters who use camouflage, stealth, and guile to catch their prey. However, these tools pale before their greatest weapon: the little octopuses are among the most poisonous creatures on planet Earth.
Like the flamboyant cuttlefish, the blue-ringed octopus does not like to bite without giving warning but advertises its toxicity with vivid coloration. The octopus can conceal itself with tremendous prowess however, as soon as it becomes aware of a predator or some other threat, it dials up its coloration changing from muted reef tones to brilliant yellow with iridescent blue rings. If you see something like this in the ocean, for heaven’s sake don’t touch it. The octopus’s warning colors let ocean predators know to leave it alone but immediately attract humankind’s magpie urge to grab shiny things. Although blue-ringed octopuses are good natured and have been known not to bite people who were provoking them rather intensely, their bites have caused more than seventy recorded fatalities in Australia. The octopus has a tiny beak and often a victim does not realize they have been bitten until they began to fall into paralysis and their respiration starts to fail.
The venom of the blue ringed octopus is a complicated pharmacological cocktail which includes tetrodotoxin, 5-hydroxytryptamine, hyaluronidase, tyramine, histamine, tryptamine, octopamine, taurine, acetylcholine, and dopamine. The most active ingredient tetrodotoxin blocks the sodium channels which conducting sodium ions (Na+) through a cell’s plasma membrane. This causes total paralysis for the octopus victim, however if clever and persistent rescuers are present at the time of the bite they can rescue the unfortunate soul with continuous artificial respiration. This is no small matter as bite victims are often rendered completely unresponsive by the paralytic victim. Although completely conscious they are unable to communicate in any way or even breathe. If artificial respiration is initiated immediately and continued until the body can metabolize and eliminate the toxin, bite victims can survive (although it sounds like rather an ordeal).
Blue ringed octopuses are tender and solicitous mothers. The mother octopus lays a clutch of approximately 50 eggs in autumn which she incubates beneath her arms for about six months (during which time she is unable to eat). When the eggs hatch, the mother octopus dies. The baby octopuses reach sexual maturity in about a year. Despite their cleverness and beauty, the animals are as ephemeral as they are deadly.
There are about 120 living species of marine mammals (although that total may tragically become much smaller in the very near future). Of this number, only one species is herbivorous. The mighty dugong (Dugong dugon) is the last animal of its kind, a gentle lumbering remnant of the giant herds of sirenian grazers which once graced the world’s oceans. Dugongs are distinct from the three extant species of manatees (the world’s other remaining sirenians) in that they never require fresh water at any point of their lives. Additionally dugongs possess fluked tails in the manner of dolphins and whales.
Dugongs live in shallow tropical waters of the Indian Ocean and the Pacific Ocean. They range from Madagascar to the Philippines, but are only common along the north coast of Australia (where conservation efforts and a limited human population have allowed them to live in peace). Dugongs can swim in deep oceans for a limited time, but prefer to stay on continental shelves where they can feed on seagrass and marine algae. Their all-salad diet does not prevent them from growing to substantial size: some individuals have been known to reach more than 3.5 meters in length (11 feet) and weigh over 950 kilograms (nearly a ton). Although Dugongs can live more than seventy years, they reproduce extremely slowly. Females gestate for over a year and then suckle their calf for around 18 months. Calves may stay with their mothers for many years after being weaned and need almost contact with their mothers for security and affection until they are almost grown. Young dugongs swim with their short paddle-like flippers, but adults use their tail for propulsion and only steer with their flippers.
Dugongs have a variety of vocalizations with which they communicate. Usually they live in small family units. Great herds are not unknown but seagrasses do not grow in sufficient quantity to support such numbers together for long.
Like the other sirenians, Dugongs have dense bones with almost no marrow (a feature known as pachyostosis). It has been speculated that such heavy skeletons help them stay suspended just beneath the water in the manner of ballast. The lungs of dugongs are extremely elongated, as are their large elaborate kidneys (which must cope with only saltwater). Additionally, the blood of dugongs clots extremely rapidly.
Dugongs face a number of natural threats, particularly storms, parasites, and illnesses. Because of their large size they are only preyed upon by alpha predators such as large sharks, killer whales, and salt-water crocodiles. As with other marine animals, the greatest dangers facing dugongs come from humankind. For millennia Dugongs have been hunted for meat, oil, and ivory. Traditional medicine from various portions of their range (wrongly) imputes magical properties to parts of their bodies. Worst of all, dugongs are frequent victims of boat collisions or are killed as by-catch by fishermen trying to catch something else.
One of the most delicate and exquisite shells of the world belongs to the Venus Comb Murex (Murex pectin) a predatory snail which hunts in the tropical waters of the Indo-Pacific. The snail is covered by over one hundred tapered spines which protect it from predators and support the creature (in the fashion of a snowshoe) when it traverses soft muds. The Venus Comb Murex hunts small mollusks, tunicates, worms, and crustaceans. When one handles the delicate 15 cm long shell it is strange to imagine that it belonged to a fearsome hunter. The Venus Comb Murex is a member of the Murexes, medium to large gastropods within the family Muricidae. Murexes were described by Aristotle–who used the exact same name for them.