The World’s Biggest Chordates!

What is a chordate?

The chordates are a group (actually, a phylum) of animal. They are distinguished from other animals in that they have something like a “backbone” – a tube down their back, containing an important nerve. Most chordates are vertebrates. In vertebrates, this tube is usually made of vertebra, a special kind of bone, with flexible plates between each vertebra allowing the animal to bend its back to a certain degree. The world’s largest chordate is a vertebrate, and is, in fact, the world’s largest animal – Blue Whale. Other features most chordates share are :

• A tail, which it moves using muscles,
• A hollow or slitted mouth,
• An area at the back of the throat for making mucous (that’s right, almost all chordates make snot!).

What kinds of chordates are there?

The phylum of the chordates, called Chordata, is divided three main groups (called subphyla). These in turn are divided into a large number of classes.

• The Vertebrates : in these animals, the cord is usually made of bones. This includes us, and also the Blue Whale, as well as fish, birds, reptiles and amphibians. Over 57000 of the 63000 species of chordate are actually vertebrates.
  • The fish – actually, there are several quite different classes of animals, all called fish. The most well-known are the Cartiligenous fishes (Condrichthyes) and the Bony fishes (or “normal” fish!) which includes the two classes Actinopterygii and the Sarcopterygii. A list of all the known classes of fish follows.
    • The Acanthodii, sometimes called Spiny Sharks, are an extinct group of fish that had some characteristics of Cartiliginous fish, and others of bony fish.
    • The Actinopterygii are the largest class of fish, in fact, the largest class of vertebrates! There are 27000 species of these, “ray-finned” fish, living in both sea and fresh water.
    • The Cephalaspidomorphs are a group of extinct jawless fishes. Actually, scientists are divided as to what animals exactly should belong to this group – some say the lampreys should be included, others disagree.
    • The Condrichthyes are the cartiligenous fishes, including sharks and rays. These fish don’t have true bone, instead, their skeleton is made of cartilige.
    • The Conodonts : a group of extinct worm-like animals, known mainly from their fossilized teeth.
    • The Hyperoartia is the class of the Lampreys, a group of eel-shaped sea animals, that are so different from fish, that scientists put them in a different group altogether.
    • The Myxini : these are the Hagfish – they look a bit like eels, and can tie themselves into knots.
    • The Placoderms : another group of extinct fish, which had hard plates to protect their heads.
    • The Pteraspidomorphs : a group a extinct fish, which didn’t have jaws.
    • The Sarcopterygii, or lobe-finned fish, include the lungfish, and the once-thought-extinct coelacanths.
  • The other classes of vertebrate are
    • The amphibians (Amphibia). These are the frogs, newts, toads, salamanders, axolotls. These are vertebrates that can breathe both air and water.
    • The reptiles (Sauropsida). These are the turtles, lizards, snakes and other land vertebrates with scales.
    • Synapsida is a group of creatures most of us would call dinosaurs, but which differed from other dinosaurs so much they were given their own class.
    • The birds (Aves). Mostly feathered, and mostly able to fly.
    • The mammals (Mammalia). These warm-blooded creatures mostly have hair, and all give milk to their young.
• Cephalocordata is a group of animals whose back-“bone” actually is not made of bone, but by a tough leathery tube.
• Finally, the Urochordata are animals which have a nerve cord along their back, but only as young. When they grow up, the cord disappears. There are three classes of urochordata.
  • Baby sea squirts (Ascidiacea) look like little tadpoles, and swim about. The adult, however, attaches itself to a rock, loses its tail (and nerve cord), and filters its food from the water that passes it by.
  • The Thaliacea are like the sea squirts in many ways, but just float around for their whole lives instead of attaching to a rock.
  • The Larvacea build cellulose bubbles around themselves that they use like a filter to concentrate their food.

What is the world’s biggest chordate?

The world’s largest chordate in every way is the Blue Whale. It can grow up to 30 metres (100 feet) long or more, and weigh around 140 tonnes – that’s 140000 kg, or 300000 pounds! It is even bigger than the largest dinosaurs ever were. Sadly, it almost went the way of the dinosaurs in the 20th century, due to whaling. Hunting of Blue Whales was banned in the 1960s, and finally ended in the 1970s. Even now, the population of blue whales is still less than 1% of what it was before whaling began, and some scientists fear they may never recover their former numbers.