Life on Earth began in the sea, which is why there is a far greater diversity of life forms (phyla) living in the sea than on land. These include some bizarre adaptations not seen elsewhere, such as deadly fishes that look like rocks, hungry worms like colourful feather-dusters, crabs that make gardens of other creatures on their backs, and microscopic worms that live between grains of sand, to the largest living animals on the planet – the whales.
Not only are there many more phyla of marine animals, but their body plans, colours, patterns, appendages and other features often appear to be radically different from those more familiar terrestrial animals. These adaptations generally relate to a particular biological function that confers a survival advantage to species living in the sea, and which have persisted for many millions of years. Consequently, many marine animals alive today do have not appear to have changed substantially from their ancestors in these ancient seas, hundreds of millions of years ago, long before life colonised the land. These range from camouflage or warning (toxic, dangerous) colouration, patterns and behaviours, to strange appendages each adapted for walking, swimming, feeding, communicating, mating and fighting – sometimes all found on the one species. Other species have evolved more concealed features, such as producing unique chemicals for digesting food, fighting, and defending against other animals, of which some have lead to discoveries of new kinds of life enhancing drugs for human-kind. Today, however, we know most about marine biodiversity from only the first 30 metres or so surrounding our continents and islands, and consequently there are undoubtedly many more species awaiting discovery than we presently know.
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