'Squat lobster' photobombs Shackleton's Endurance ship

Filter-feeders were expected but this squat lobster was a very pleasant surprise

While the world gaped at the extraordinary preservation of Shackleton's Endurance ship, one group of people were agog at something else in the crystal clear underwater footage.

These were polar biologists, and they were wrapped up in the different animals they could see.

There were the expected invertebrates - filter-feeders such as sea anemones and sea lilies - but some surprises, too.

The star, undoubtedly, was the squat lobster seen climbing over the wreck.

It was scuttling past a porthole on the famous wooden ship which sank to the bottom of the Weddell Sea in 1915 after being crushed by sea-ice.

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Squat lobsters aren't really lobsters at all, being more closely related to some species of crabs.

It's hard to be sure given the resolution of the released imagery but the animal could be from the Munidopsis genus, says Dr Huw Griffiths from the British Antarctic Survey (BAS), who was not on the expedition to find Endurance.

"Munidopsis is a genus of squat lobster with over 200 known species," he told BBC News.

"Its members are mainly found on continental slopes and on abyssal plains. One record of a species, M. albatrossae, was found in 2006 in the Bellingshausen Sea on the western side of the Antarctic Peninsula.

"But this is a first for the Weddell Sea, if you discount fossils found on Seymour Island further to the north."

Munidopsis squat lobsters will live at great depth. One species is known to eat wood

Confirmation will require further analysis of the much higher resolution imagery gathered by the Endurance22 project.

Its submersibles were equipped with 4K cameras that swept back and forth across the wreck to make a detailed photogrammetric record.

The lost ship from Sir Ernest Shackleton's ill-fated Imperial Trans-Antarctic expedition of 1914-1917 was identified on Saturday after a two-and-a-half-week search.

That there are so many filter-feeders covering the wreck is no surprise.

These animals will colonise anything that stands proud of the ocean floor, which in this region of the Weddell Sea would include boulders dropped by passing icebergs. Getting even just a few centimetres above the sediment gives greater opportunity to catch particles of food in the bottom currents.

Creatures such as sea squirts will pump water in and out through their two syphons to collect plankton and "marine snow", which is essentially dead things and faeces that rain down from the sea surface.

• Sea lilies are the stalked variety of crinoids

• Adult animals anchor themselves to the seabed

• Their crowns try to bend into the water current

• Feathery pinnules catch floating food particles

• This detritus is propelled down towards a mouth

Water current from the right in image

One organism in the new pictures of Endurance really catches the eye - and that's a yellow crinoid, or sea lily - an animal, not a plant. It's anchored just under the taffrail, or hand rail, on the stern of the ship.

There's an interesting fan-like structure near the ship's wheel that Dr Michelle Taylor reckons is a hydroid.

"Hydroids are colonial animals that live in little box-like high rises together," the Essex University marine biologist told BBC News.

"They are the fine, slightly stingy, fur that you find covers the bottom of boats very quickly. Pop your head into any dock and look for anything with very fine hairs and that's probably a hydroid."

It was widely anticipated that Endurance would be in a decent state of preservation.

The types of worms that routinely devour wooden structures at higher latitudes are not present in the waters around the White Continent.

This in part is because of the absence of a source of wood going into the ocean in that region. There are no forests on Antarctica and there haven't been for millions of years.

Organisms adapted to such nourishment would therefore have slim pickings.

Marine zoologist Prof Simon Cragg from Portsmouth University says the Antarctic Circumpolar Current that moves around the White Continent also works to keep wood borers from moving closer to the polar south.

"Shipworms have been the bane of wooden ships throughout history and determined ship design from the classical Greek period through to Nelson's time and even today. Decay of wood by marine bacteria and marine fungi is very slow, especially at low temperatures," he added.

Marine biologists have had only the briefest of glimpses of what's living on Shackleton's ship. The Endurance22 project released just a 90-second sequence of video on Wednesday. When longer views become available, who knows what else will be revealed to have taken up residence.

"There are plenty of mysteries left to solve," said Dr Griffiths.

The Endurance was trapped in sea-ice for months before sinking to the deep in 1915

The project to find the lost ship was mounted by the Falklands Maritime Heritage Trust (FMHT), using a South African icebreaker, Agulhas II