Tigerfish
Tigerfish is the common name for a variety of species from several different families of fish, usually on account of their colouration or otherwise fearsome appearance.
Several species in the genus Hydrocynus of the family Alestiidae are called "tigerfish" and are particularly prized as gamefish. These African fish are found in many rivers and lakes on the continent and are fierce predators with distinctive protruding teeth.
The two most common species are probably most recognizable in Southern Africa. The first is the Goliath Tiger (Hydrocynus goliath), which is found in the Congo River system, the largest of the family. The second-largest, and the southernmost species, is the Tigerfish (Hydrocynus vittatus), commonly found in the Zambezi River and in the two biggest lakes along the Zambezi, Lake Kariba in Zambia, Zimbabwe, and Cabora Bassa in Mozambique and Jozini dam in South Africa.
The name "tigerfish" has occasionally been used for species of cichlid in the genus Rhamphochromis. These are large, silver-colored fishes that may have one or two black horizontal lines running the length of the body. These fish are native to Lake Malawi in Africa. They can measure up to 2 meters (6 ft. 7 in.) in length and weigh up to 50 kg (105 lbs.) They also have very sharp teeth that can rip through skin easily; however, they are not known to eat humans.
Tigerfish can be considered Africa's equivalent of the South American piranha, though they belong to a completely different family, as they are famous for their ferocity when hunting. They have razor-sharp teeth that are interlocking, along with streamlined, muscular bodies built for speed. Tigerfish are aggressive predators. A tigerfish has a gas-filled sac in its body that it uses as a sound receiver. This transmits vibrations from the water, enabling it to detect any animals nearby and respond accordingly. A school of juveniles can tackle animals of almost any size, including any land animals that stray too close to the water's edge. Adults tend to travel in smaller groups of four or five, but they are no less dangerous. Even an individual can take down prey as large as itself. When food is scarce or the competition for food is too great, tigerfish may resort to cannibalism. This is particularly common in the dry season. Tigerfish have also been known to attack humans, these attacks can be devastating owing to their sharp teeth and aggressive hunting tactics.
Senegal Bichir
The Senegal Bichir, Polypterus senegalus, also known as the Gray Bichir and Cuvier's Bichir, is sometimes called the "dinosaur eel" at many local pet chains - a misnomer, as the creature is not an eel. It is a fish, a prototypical species of the Polypterus genus, meaning most of its features are held across the genus.
The body is long and about as deep as it is wide. A serrated dorsal fin runs along most of the body until it meets the caudal fin. The pectoral fins attach just behind and below the gill openings and are the primary means of locomotion, providing a slow, graceful appearance. P. senegalus is smaller than its brethren, reaching about 35.5 cm (14").
The head is small and lizard-like with a gaping mouth and small eyes on either side. Since its eyesight is poor the bichir primarily hunts by smell. External nostrils protrude from the nose of the fish to enable this.
The fish has a pair of primitive lungs instead of a swim bladder, allowing it to periodically gulp air from the surface of the water. In the aquarium bichirs can be observed dashing to the surface for this purpose. Provided the skin remains moist, the creature can remain out of the water for near indefinite periods of time.
This bichir's skin serves as a particularly effective armor.
Bichirs are predatory fish and in captivity will take any live or dead animal that can be swallowed or broken apart and then swallowed. The only thing preventing a bichir from emptying an aquarium of smaller fish is its speed; the pectoral fins only allow for slow cruising, and while it can achieve amazing bursts of speed, it can't catch fish of average speed. Given enough time, any fish that can fit in the bichir's mouth will be eaten; this fish should not be kept with any other fish smaller than three inches.
Ocean Gyre
A gyre in oceanography is any large system of rotating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis Effect; planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque). The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, but it is most commonly used in oceanography, to refer to the major ocean systems.
The following are the five most notable gyres: North Atlantic, South Atlantic, Indian Ocean, North Pacific and South Pacific.
Tropical gyres are less unified and tend to be mostly east-west with minor north-south extent. These include the Atlantic Equatorial Current System, Pacific Equatorial Current System and the Indian Monsoon Gyres.
The center of a subtropical gyre is a high pressure zone. Circulation around the high pressure is clockwise in the northern hemisphere and anticlockwise in the southern hemisphere, due to the Coriolis effect. The high pressure in the center is due to the westerly winds on the northern side of the gyre and easterly trade winds on the southern side of the gyre. These cause frictional surface currents towards the latitude at the center of the gyre. The build-up of water in the center of the gyre creates equatorward flow in the upper 1,000 to 2,000 m (3,300 to 6,600 ft) of the ocean, through rather complex dynamics. This equatorward flow is returned poleward in an intensified western boundary current.
The intensified western boundary current of the North Atlantic Gyre is the Gulf Stream, in the North Pacific it's the Kuroshio Current, in the South Atlantic it's the Brazil Current, in the South Pacific it's the East Australian Current, and in the Indian Ocean it's the Agulhas Current.
Subpolar gyres form at high latitudes (around 60°). Circulation of surface wind and ocean water is anticlockwise in the Northern Hemisphere, around a low-pressure area, such as the persistent Aleutian Low and the Icelandic Low. Surface currents generally move outward from the center of the system. This drives the Ekman transport, which creates an upwelling of nutrient-rich water from the lower depths.
Subpolar circulation in the southern hemisphere is dominated by the Antarctic Circumpolar Current, due to the lack of large landmasses breaking up the Southern Ocean. There are minor gyres in the Weddell Sea and the Ross Sea, the Weddell Gyre and Ross Gyre, which circulate in a clockwise direction.
Basilosaurus
Basilosaurus ("King Lizard") is a genus of cetacean that lived from 40 to 34 million years ago Its fossilized remains were first discovered in the southern United States (Louisiana), and were initially believed to be some sort of reptilian sea monster, hence the suffix -"saurus", but later it was found that was not the case. Fossils from at least two other species of this taxon have been found in Egypt and Pakistan. in the Late Eocene.
Basilosaurus averaged about 18 meters (60 ft) in length, and is believed to have been the largest animal to have lived in its time. It displayed an unparalleled degree of elongation compared with modern whales. Their very small vestigial hind limbs have also been a matter of interest for paleontologists. The species is the state fossil of Mississippi and Alabama in the United States.
During the early 19th century in the American South, Basilosaurus cetoides fossils were so common (as well as large) that they were regularly used as furniture. Vertebrae were sent to the American Philosophical Society by a Judge Bly of Arkansas and Judge John Creagh of Clarke County, Alabama. Both fossils ended up in the hands of the anatomist Dr. Richard Harlan, who requested more examples from Creagh. With some reservation, Harlan speculated that the fossils belonged to a (50 m [166 ft] long) marine reptile, for which he suggested the name Basilosaurus, meaning “King reptile”.
When the British anatomist Sir Richard Owen studied the spine, mandibular fragments, arms, and ribs (more recently found) he proclaimed them to be mammalian. Owen proposed renaming the find to Zeuglodon cetoides (“whale-like yoke teeth”), which is now a junior synonym; though the latter is considered by many to be a more fitting name, the first-published name always takes precedence. The name Zeuglodon refers to the double rooted teeth typical of marine mammals.
In 1845, “Dr.” Albert Koch heard stories of giant bones in Alabama, and went down to cobble together a full skeleton. He eventually created a huge 114-foot (35 m) skeleton of a “sea serpent” he called "Hydrarchos", which he displayed in New York City, and later Europe. It was eventually shown to have come from 5 different individuals, some of which were not Basilosaurus. The remains were eventually destroyed in the Great Chicago Fire.
Fossil finds of another species, Basilosaurus isis, have been found in the aptly named Valley of the Whales in Egypt. The fossils were very well preserved, hind limbs included, and were rather numerous. Paleontologist Philip Gingerich, who organized several expeditions to the valley, speculated that Egyptian crocodile worship may have been inspired by the huge skeletons that lay there. Fossil remains of another species, Basilosaurus drazindai, have been found in Pakistan. Another fossilized species named Basiloterus husseini was its closest known relative, but was not as large or elongated.
Seven-Arm Octopus
The Seven-arm Octopus (Haliphron atlanticus) is the largest known species of octopus based on scientific records, with a total estimated length of 4 m and weight of 75 kg. However, there have been disputed claims of even larger octopuses of the species Enteroctopus dofleini.
The Seven-arm Octopus is so named because in males the hectocotylus (a specially modified arm used in egg fertilization) is coiled in a sac beneath the right eye. Due to this species' thick gelatinous tissue, the arm is easily overlooked, giving the appearance of just seven arms. However, like other octopuses, it actually has eight.
In 2002, a single specimen of giant proportions was caught by fisheries trawling off the eastern Chatham Rise, New Zealand. This specimen, the largest of this species and of all octopuses, was the first validated record of Haliphron from the South Pacific. It had a mantle length of 0.69 m, total length of 2.90 m, and weight of 61.0 kg, although it was incomplete.
The type specimen of H. atlanticus was collected in the Atlantic Ocean at 38°N 34°W. It is deposited at the Zoologisk Museum, University of Copenhagen.
Sea Squirt
Tunicates, also known as urochordates, are members of the subphylum Tunicata or Urochordata, a group of underwater saclike filter feeders with incurrent and excurrent siphons that is classified within the phylum Chordata. While most tunicates live on the ocean floor and are commonly known as sea squirts and sea pork,others – such as salps, doliolids and pyrosomes – live above in the pelagic zone as adults.
Most tunicates feed by filtering sea water through pharyngeal slits, but some are sub-marine predators such as the Megalodicopia hians. Like other chordates, tunicates have a notochord during their early development, but lack myomeric segmentation throughout the body and tail as adults. Tunicates lack the kidney-like metanephridial organs, and the original coelom body-cavity develops into a pericardial cavity and gonads. Except for the pharynx, heart and gonads, the organs are enclosed in a membrane called an epicardium, which is surrounded by the jelly-like mesenchyme. Tunicates begin life in a mobile larval stage that resembles a tadpole, later developing into a barrel-like and usually sedentary adult form.
Tunicates apparently evolved in the early Cambrian period, beginning c 540 million years ago. Despite their simple appearance, tunicates are closely related to vertebrates, which include fish and all land animals with bones.
Most tunicates are hermaphrodites. The eggs are kept inside their body until they hatch, while sperm is released into the water where it fertilizes other individuals when brought in with incoming water.
Some larval forms appear very much like primitive chordates with a notochord (stiffening rod). Superficially, the larva resemble small tadpoles. They swim with a tail, and may have a simple eye, or Ocellus, and balancing organ, or Statolith. Some forms have a calcereous spicule that may be preserved as a fossil. They have appeared from the Jurassic to the present, with one proposed Neoproterozoic form, Yarnemia.
The larval stage ends when the tunicate finds a suitable rock to affix to and cements itself in place. The larval form is not capable of feeding though it may have a digestive system, and is only a dispersal mechanism. Many physical changes occur to the tunicate's body, one of the most interesting being the digestion of the cerebral ganglion, which controls movement and is the equivalent of the human brain. From this comes the common saying that the sea squirt "eats its own brain". In some classes, the adults remain pelagic (swimming or drifting in the open sea), although their larvae undergo similar metamorphoses to a higher or lower degree.
Once grown, adults can develop a thick covering, called a tunic, to protect their barrel-shaped bodies from enemies.
Tunicates are suspension feeders. They have two openings in their body cavity: an in-current and an ex-current siphon. The in-current siphon is used to intake food and water, and the ex-current siphon expels waste and water. The tunicate's primary food source is plankton. Plankton gets entangled in the mucus secreted from the endostyle. The tunicate's pharynx is covered by miniature hairs called ciliate cells which allow the consumed plankton to pass down through to the esophagus. Their guts are U-shaped, and their anuses empty directly to the outside environment. Tunicates are also the only animals able to create cellulose.
Tunicate blood is particularly interesting. It contains high concentrations of the transition metal vanadium and vanadium-associated proteins as well as higher than usual levels of lithium. Some tunicates can concentrate vanadium up to a level one million times that of the surrounding seawater. Specialized cells can concentrate heavy metals, which are then deposited in the tunic.
Glass Sponge
Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed silaceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma.
Glass sponges are relatively uncommon and are mostly found at depths from 450 to 900 metres (1,480 to 3,000 ft) although the species Oopsacas minuta has been found in shallow water, while others have been found much deeper. They are found in all oceans of the world, although they are particularly common in Antarctic waters.
They are more-or-less cup-shaped animals, ranging from 10 to 30 centimetres (3.9 to 12 in) in height, with sturdy lattice-like internal skeletons made up of fused spicules of silica. The body is relatively symmetrical, with a large central cavity that, in many species, opens to the outside through a sieve formed from the skeleton. Unlike other sponges, they tend to be present as individuals, rather than forming large fused colonies. They are generally pale in colour.
Much of the body is composed of syncitia, extensive regions of multinucleate cytoplasm. In particular, the epidermal cells of other sponges are absent, being replaced by a syncitial net of amoebocytes, through which the spicules penetrate. Unlike other sponges, they do not possess the ability to contract.
One ability they possess is a unique system for rapidly conducting electrical impulses across their bodies, making it possible for them to respond quickly to external stimuli. Glass sponges like "Venus' Flower Basket" have a tuft of fibers that extends outward like an inverted crown at the base of their skeleton. These fibers are 50 to 175 millimetres (2.0 to 6.9 in) long and about the thickness of a human hair. They work as optical fibers somewhat similar to those used in modern telecommunication networks.
These creatures live for a very long time, but the exact age is hard to measure; one study based on modelling gave an estimated age of a specimen of Scolymastra joubini as 23,000 years, which is thought impossible, but is the basis for a listing of ~15,000 years in the AnAge Database.
