"click here to view a slideshow of some of the creatures mentioned in this article"

Experts compiling a massive marine-life census have also uncovered an Antarctic expressway where octopuses ride a flow of extra salty water, sharks congregating in a deep sea "café", and a new mid-Atlantic subsea "continent".

The World Conference on Marine Biodiversity, which opens in Spain tomorrow, will hear that at least 110 new species have been confirmed among more than 5,300 "possibles" during the ten-year census, which will be completed in 2010.

The number of fish species alone is expected to be boosted by 4,000 – one quarter – to 16,000, because just 5 per cent of the world's oceans have yet been surveyed. More than 2,000 scientists from 82 countries are taking part in the project, including the UK.

Myriam Sibuet, a French deep-sea explorer and vice-chair of the census, said: "The impressive number of landmark findings over the past two years reveals the richness of what remains to be discovered."

The latest new creatures include giant Macroptychaster sea stars, found off New Zealand, which grow up to 2ft (60cm) across. Sea spiders as large as dinner plates have also been seen.

A giant 1.3ft (40cm) aplacophoran mollusc, Chaetoderma felderi, was collected in the deep off Louisiana in the United States – twice as long as the previous largest in its sub-class.

Giant bacteria have been discovered in the eastern south Pacific, which researchers believe may be "living fossils" that developed in the earliest ocean when there was little or no oxygen.

They even think this ability to survive without oxygen could provide an important clue in the search for extraterrestrial life.

Other discoveries include evidence that most deep-sea octopus species evolved from a common ancestor in Antarctica.

They started migrating more than 30 million years ago using a northbound "thermohaline expressway" of very salty, high-oxygen water as the continent cooled and its ice sheet grew.

Spread round the globe, many different octopus species evolved, some losing their defensive ink sacs which were redundant in the pitch-dark depths.

Satellite tagging of white sharks has shown they travel long distances every winter to spend six months in the Pacific, making frequent, repeated communal dives to "cafés" 975ft (300m) deep. Scientists believe these may be important for feeding or reproduction.

Researchers are also surveying a "new continent" – the mid-Atlantic Ridge, up to 1.5 miles (2.5km) deep, which is home to hundreds of species rare or unknown elsewhere. It includes the Ashadze, the world's deepest known active hot vent, 2.5 miles (4.1km), down and populated by anemones, worms and shrimp.