Look up a chambered nautilus in a book or on the web will reveal they are in the same class of mollusks as octopuses, squid and cuttlefish. The first thing that sets this cephalopod apart from the rest of the group is that the nautilus date back more than 500 million years, and were once the dominant form of life in the ocean. And to share a night dive with one of these true living fossils is a very fortunate event.

It's large, fan-like fins wave and flare like the skirts of a Flamenco dancer, revealing vibrant shades of rust and orange with flashes of royal blue as it hunts its prey under the cover of night. As beautiful as its dance may be, one prick from one of its long dorsal spines will inflict a very painful burning sensation.

Renowned diving physiologist Dr Neal W Pollock filmed a EUROTEK TEKTalk where he discussed the foundations of decompression physiology, M Values and what Gradient Factors are.

Pollock is the Research Director at Divers Alert Network (DAN) and a Research Associate at the Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center. Both positions are based in Durham, North Carolina.

Sweden's military has now analyzed the video footage provided by Swedish wreckhunter group Ocean X Team and concluded that it is the wreck of a Russian submarine that sank after a collision with a Swedish vessel in 1916 during the First World War. Ocean X was the team who also found the "Baltic anomali"