Sea snake toxins are far more venomous than the toxins of land snakes. While some species have gentle dispositions and bite only when provoked, others are much more aggressive, especially during mating season. Postsynaptic neurotoxins in the venom are capable of paralysing the respiratory system of the victim.
All sea snakes have paddle-like tails and many have laterally compressed bodies that give them an eel-like appearance. They do not have gills and must surface regularly to breathe. They are found in warm coastal waters from the Indian Ocean to the Pacific.
Box jellyfish are well-known for their incredibly potent venom. The species Chironex fleckeri, Carukia barnesi and Malo kingi are among the most venomous creatures in the world. Stings from these and a few other species in the class are extremely painful and can be fatal. Each tentacle includes about 500,000 cnidocytes. Each cnidocyte contains a nematocyst, a harpoon-shaped microscopic mechanism that injects venom into the victim.
The amount of venom in one box jellyfish is said to be enough to kill 60 humans with one sting. Deaths attributed to box jellyfish range from 20 to 40 annually in the Philippines, but the US National Science Foundation believes this figure could be a serious underestimate. Notorious species of box jellies are restricted to the tropical Indo-Pacific, with other species found in tropical oceans worldwide.
The name of the stonefish originates from the stonefish’s ability to camouflage itself with a grey and mottled colour similar to that of a stone. It is one of the most venomous fish currently known in the world. Stonefish secrete potent neurotoxins from glands at the base of thirteen dorsal spines which stick up when disturbed or threatened.
When the stonefish is disturbed, the amount of venom injected into the victim is proportional to the amount of pressure applied. Muscle weakness, shock and temporary paralysis are all symptoms of stonefish venom, though their severity depends on the number of spines involved and their penetration depth.
Stonefish are primarily marine and found in the coastal regions of Indo-Pacific oceans as well as off the coast of Florida and in the Caribbean.
The tiger shark is a large macropredator, capable of attaining a length of over 5 m (16 ft). The dark stripes on its body resemble the patterning of a tiger, lending themselves to the shark’s name. The stripes fade as the shark matures.
The tiger shark is a solitary and mostly nocturnal hunter. They probably have the most perfect teeth structure of all sharks. Due to its tendency to eat virtually anything it encounters, including inedible man-made objects that linger in its stomach, the tiger shark has been nicknamed “the garbage can of the sea”. Even terrestrial mammals have been found in their stomachs.
Tiger sharks are second only to the Great White in terms of numbers of human fatalities recorded. The tiger shark is found in many tropical and temperate waters and is especially common around central Pacific islands.
Pufferfish are generally believed to be the second-most poisonous vertebrates in the world, after the golden poison frog. Internal organs such as the liver, and sometimes the skin, are highly toxic to most animals when eaten. Nevertheless, the meat of some pufferfish species is considered a delicacy in Japan, called fugu.
Pufferfish ‘puff up’ to protect themselves by ingesting large amounts of water, causing them to expand to several times their normal size.
Pufferfish tetrodotoxin paralyses the diaphragm muscles and stops any human victim from breathing. Tetrodotoxin is up to 1,200 times more deadly than cyanide to humans and has no known antidote. People who live longer than 24 hours typically survive, although possibly after a coma lasting for several days. Pufferfish are most diverse in the tropics, relatively uncommon in the temperate zone and completely absent from cold waters.
Stingrays are usually very docile and curious. Their typical reaction is to flee any disturbance. Nevertheless, certain larger species may be more aggressive and should be approached with caution as the stingray’s defensive reflex – use of its poisoned stinger – may result in serious injury and death. The location of the penetrative injury caused by the stinger can also play a role in any fatal accidents, as was the case in the death of wildlife personality Steve Irwin.
The venomous barb is covered in many flat spines that feature two grooves on their undersides. These contain venom-secreting cells, enclosed in an epidermis that rips open when embedded in flesh. Furthermore the spines are made of vasodentin, a cartilaginous product that easily cuts flesh.
Stingrays are common in coastal tropical and subtropical marine waters throughout the world.
The existence of the colossal squid is no myth. Current estimates put its maximum size at 12–14 metres (39–46 ft), making it the largest known invertebrate. Unlike the giant squid, whose arms and tentacles only have suckers lined with small teeth, the colossal squid’s limbs are also equipped with sharp hooks: some swivelling, others three-pointed.
The colossal squid also has the largest eyes documented in the animal kingdom; the eyes of one partly collapsed specimen measured 27 cm (11 in). The beak of the colossal squid is the largest known of any squid.
It is believed that the colossal squid’s main predator is the sperm whale. Much of the information known about the colossal squid has been garnered from samples taken from the stomachs of sperm whales. Primarily, the colossal squid is an inhabitant of the entire circumantarctic Southern Ocean.
The Moray eel’s jaws are wide and frame a protruding snout. They are fierce predators with most possessing large teeth used to tear flesh or grasp slippery prey items.
Morays are frequently thought of as particularly vicious or ill-tempered animals. In truth, morays normally hide from humans in crevices and would rather flee than fight. They are shy and attack humans only in self-defence, or when they have lost their fear of humans. One occasion in 2005 when a Moray eel bit off the thumb of a diver was due to a lack of caution – divers often fed one particular large Moray eel and when struggling to open a packet of sausages for the eel the diver suffered a regrettable but perhaps predictable misfortune.
Eels that have eaten certain types of toxic algae can cause ciguatera fish poisoning if eaten. They are present in warmer oceans all around the world and typically found around coral reefs.