Swiming sea cucumbers, video


This 14 June 2019 video says about itself:

Weird and Wonderful: Swimming sea cucumbers

It can be hard to move from place to place for many animals that live on the seafloor and move slowly. Most sea cucumbers (Holothurians) live a sedentary life on the bottom of the ocean, eating sediment or detritus that rains down from above. But some sea cucumbers leave the life of eating and pooping on the seafloor temporarily by swimming. They may do this as a defense behavior, or to find a mate. Sea cucumbers have made remarkable adaptations to master the challenges of living in the deep sea.

For more information on the importance of holothurians in deep ecosystems see here.

Advertisements

Cambrian age sea star ancestor discovery


This June 2018 video is called The Evolution of Echinoderms.

From Ohio State University in the USA:

Scientists discover evolutionary link to modern-day sea echinoderms

Research team solves fossil mystery, identifies new species

May 2, 2019

Scientists at The Ohio State University have discovered a new species that lived more than 500 million years ago — a form of ancient echinoderm that was ancestral to modern-day groups such as sea cucumbers, sea urchins, sea stars, brittle stars and crinoids. The fossil shows a crucial evolutionary step by echinoderms that parallels the most important ecological change to have taken place in marine sediments.

The discovery, nearly 30 years in the making, was published recently in the Bulletin of Geosciences and provides a clue as to how creatures were able to make the evolutionary leap from living stuck to marine sediment grains — which were held together by gooey algae-like colonies, the original way that echinoderms lived — to living attached to hard, shelly surfaces, which is the way their modern-day descendants live now on the bottom of the ocean.

“It throws light on a critical time, not just in the evolution of organisms, but also in the evolution of marine ecosystems,” said Loren Babcock, co-author of the study and professor of earth sciences at Ohio State. “This represents a creature that clearly was making the leap from the old style of marine ecosystems in which sediments were stabilized by cyanobacterial mats, to what ultimately became the present system, with more fluidized sediment surfaces.”

The creature, a species of edrioasteroid echinoderm that Babcock and his researchers named Totiglobus spencensis, lived in the Cambrian Period — about 507 million years ago. (The Earth, for the record, is about 4.5 billion years old.) A family of fossil hunters discovered the fossil in shale of Spence Gulch, in the eastern part of Idaho, in 1992, and donated it to Richard Robison, a researcher at the University of Kansas and Babcock’s doctoral adviser. That part of the country is rich with fossils from the Cambrian period, Babcock said.

For years, the fossil puzzled both Babcock and Robison. But the mystery was solved a few years ago, when Robison’s fossil collection passed to Babcock after Robison’s retirement.

Once Babcock had the fossil in his lab, he and a visiting doctoral student, Rongqin Wen, removed layers of rock, exposing a small, rust-colored circle with numerous tiny plates and distinct arm-like structures, called ambulcra. Further study showed them that the animal attached itself to a small, conical shell of a mysterious, now-extinct animal called a hyolith using a basal disk — a short, funnel-like structure composed of numerous small calcite plates.

The discovery was a type of scientific poetry — years earlier, Babcock and Robison discovered the type of shell that this animal appeared to be attached to, and named it Haplophrentis reesei.

The edrioasteroid that Babcock and Wen discovered apparently lived attached to the upper side of the elongate-triangular hyolith shell, even as the hyolith was alive. They think a sudden storm buried the animals in a thick layer of mud, preserving them in their original ecological condition.

Echinoderms and hyoliths first appeared during the Cambrian Period, a time in Earth’s history when life exploded and the world became more biodiverse than it had ever been before. The earliest echinoderms, including the earliest edrioasteroids, lived by sticking to cyanobacterial mats — thick, algae-like substances that covered the Earth’s waters. And until the time of Totiglobus spencensis, echinoderms had not yet figured out how to attach to a hard surface.

“In all of Earth’s history, the Cambrian is probably the most important in the evolution of both animals and marine ecosystems, because this was a time when a more modern style of ecosystem was first starting to take hold,” Babcock said. “This genus of the species we discovered shows the evolutionary transition from being a ‘mat-sticker’ to the more advanced condition of attaching to a shelly substrate, which became a successful model for later species, including some that live today.”

In the early part of the Cambrian Period — which started about 538 million years ago — echinoderms likely lived on that algae-like substance in shallow seas that covered many areas of the planet. The algae, Babcock said, probably was not unlike the cyanobacterial mats that appear in certain lakes, including Lake Erie, each summer. But at some point, those algae-like substances became appealing food for other creatures, including prehistoric snails. During the Cambrian, as the population of snails and other herbivores exploded, the algae-like cyanobacterial mats began to disappear from shallow seas, and sediments became too physically unstable to support the animals — including echinoderms — that had come to rely on them.

Once their algae-like homes became food for other animals, Babcock said, echinoderms either had to find new places to live or perish.

Paleontologists knew that the creatures had somehow managed to survive, but until the Ohio State researchers’ discovery, they hadn’t seen much evidence that an echinoderm that lived this long ago had made the move from living stuck to cyanobacterial-covered sediment to living attached to hard surfaces.

“This evolutionary choice — to move from mat-sticker to hard shelly substrate — ultimately is responsible for giving rise to attached animals such as crinoids,” Babcock said. “This new species represents the link between the old lifestyle and the new lifestyle that became successful for this echinoderm lineage.”

Sea cucumber fossil relative discovery


This is a 3D reconstruction of Sollasina cthulhu. Tube feet are shown in different colors. Credit: Imran Rahman, Oxford University Museum of Natural History

From the University of Oxford in England:

Cthulhu‘ fossil reconstruction reveals monstrous relative of modern sea cucumbers

New species of extinct sea cucumber named Sollasina cthulhu, for its resemblance to H.P. Lovecraft’s famous monster

An exceptionally-preserved fossil from Herefordshire in the UK has given new insights into the early evolution of sea cucumbers, the group that includes the sea pig and its relatives, according to a new article published today in the journal Proceedings of the Royal Society B.

Palaeontologists from the UK and USA created an accurate 3D computer reconstruction of the 430 million-year-old fossil which allowed them to identify it as a species new to science. They named the animal Sollasina cthulhu due to its resemblance to monsters from the fictional Cthulhu universe created by author H.P. Lovecraft.

Although the fossil is just 3 cm wide, its many long tentacles would have made it appear quite monstrous to other small sea creatures alive at the time. It is thought that these tentacles, or ‘tube feet’, were used to capture food and crawl over the seafloor.

Like other fossils from Herefordshire, Sollasina cthulhu was studied using a method that involved grinding it away, layer-by-layer, with a photograph taken at each stage. This produced hundreds of slice images, which were digitally reconstructed as a ‘virtual fossil’.

This 3D reconstruction allowed palaeontologists to visualise an internal ring, which they interpreted as part of the water vascular system — the system of fluid-filled canals used for feeding and movement in living sea cucumbers and their relatives.

Lead author, Dr Imran Rahman, Deputy Head of Research at Oxford University Museum of Natural History said:

“Sollasina belongs to an extinct group called the ophiocistioids, and this new material provides the first information on the group’s internal structures. This includes an inner ring-like form that has never been described in the group before. We interpret this as the first evidence of the soft parts of the water vascular system in ophiocistioids.”

The new fossil was incorporated into a computerized analysis of the evolutionary relationships of fossil sea cucumbers and sea urchins. The results showed that Sollasina and its relatives are most closely related to sea cucumbers, rather than sea urchins, shedding new light on the evolutionary history of the group.

Co-author Dr Jeffrey Thompson, Royal Society Newton International Fellow at University College London, said:

“We carried out a number of analyses to work out whether Sollasina was more closely related to sea cucumbers or sea urchins. To our surprise, the results suggest it was an ancient sea cucumber. This helps us understand the changes that occurred during the early evolution of the group, which ultimately gave rise to the slug-like forms we see today.”

The fossil was described by an international team of researchers from Oxford University Museum of Natural History, University of Southern California, Yale University, University of Leicester, and Imperial College London. It represents one of many important finds recovered from the Herefordshire fossil site in the UK, which is famous for preserving both the soft as well as the hard parts of fossils.

The fossil slices and 3D reconstruction are housed at Oxford University Museum of Natural History.

Sea cucumber poop helps ecosystems


This 3 September 2018 video says about itself:

Sea Cucumber Poop Is Surprisingly Good For the Ecosystem | Nat Geo Wild

There are about 1,250 different species of sea cucumber across the world’s oceans. This is Thelenota anax. And yes, it’s doing what you think it’s doing. Sea cucumber poop is surprisingly important for the ecosystem.

Sea stars keep kelp forests alive


This December 2017 video says about itself:

Sunflower Seastar: Terrifying Predator? | National Geographic

This animal is more than three feet wide and one of the fastest animals in its biome! It’s also a very efficient scavenger.

From Simon Fraser University in Canada:

Sea stars critical to kelp forest resilience

August 13, 2018

A study by Simon Fraser University resource and environmental management researcher Jenn Burt reveals that sunflower sea stars play a critical role in the resilience of B.C. [British Columbia] ‘s kelp forests, which are among the most productive ecosystems on Earth. Similar to land-based forests, kelp forests provide essential habitat for species and also help remove CO2 from the atmosphere.

Burt and her team discovered sea otters and sunflower stars are complementary predators of sea urchins, which inhabit rocky reefs and voraciously eat kelp. Without natural predators, sea urchins quickly devour entire kelp forests.

“We showed that sea otters feed on large sea urchins, whereas the sunflower sea stars eat the small and medium-sized urchins that otters ignore”, says Burt. “We observed kelp density was highest at reefs with both sea otters and sunflower stars.”

The researchers made this discovery after Sea Star Wasting Disease killed 96 per cent of the sunflower star biomass on the Central coast in 2015 and 2016. During this period there was a 311 per cent increase in small and medium-sized sea urchins, which corresponded to a 30 per cent decrease in kelp density.

Burt says ecological surprises such as mass mortality events can reveal new insights into species interactions and ecosystem dynamics. She says these will become more important to learn from as climate change and other stressors make our future ocean ecosystems more unpredictable.

The combination of ocean warming and an infectious wasting disease has devastated populations of large sunflower sea stars once abundant along the West Coast of North America in just a few years, according to research co-led by the University of California, Davis, and Cornell University published Jan. 30 in the journal Science Advances: here.

California sheephead and spiny lobsters may be helping control sea urchin populations in Southern California kelp forests, where sea otters — a top urchin predator — have long been missing, according to a new study. The research provides new insight into the complex predator-prey relationships in kelp forests that can be seen in the absence of sea otters: here.

Sea urchins have gotten a bad rap on the Pacific coast. The spiky sea creatures can mow down entire swaths of kelp forest, leaving behind rocky urchin barrens. An article in the New York Times went so far as to call them “cockroaches of the ocean.” But new research suggests that urchins play a more complex role in their ecosystems than previously believed: here.

Sea urchins seeing with their feet


This 2016 video says about itself:

Conceived in the open sea, tiny spaceship-shaped sea urchin larvae search the vast ocean to find a home. After this incredible odyssey, they undergo one of the most remarkable transformations in nature.

From Lund University in Sweden:

Sea urchins see with their feet

June 12, 2018

Sea urchins lack eyes, but can see with their tentacle-like tube feet instead, previous research has indicated. Now, researchers at Lund University in Sweden have tested their vision in a new study, and shown that while sea urchins have fairly low resolution vision — it is good enough to fulfill their basic needs.

Sea urchins are currently the only animals that have been shown to see without having eyes. They see using light-sensitive cells in their tube feet, which resemble tentacles and, like the spines, are all over the body. You could say that the entire sea urchin is one single compound eye”, says John Kirwan, who conducted the study as a part of his doctoral thesis, together with colleagues at Lund University.

The tube feet have other functions besides registering light. They are used for feeding and in some species are used by the sea urchin for locomotion. Others are used to attach to surfaces or as levers to correct its position when upside down.

John Kirwan studied the sea urchin species Diadema africanum. The experiments placed the animals in water inside strongly illuminated cylinders that had various dark images on the walls.

“Ordinarily, sea urchins move towards dark areas in order to seek cover. When I notice that they react to certain sizes of images but not to others, I get a measurement of their visual acuity”, explains John Kirwan.

To obtain further data, he carried out another experiment in which he showed rapidly growing figures above the sea urchins, as a way of conjuring up an image of an approaching predator. He then registered how large the figures had to be before the sea urchins would defend themselves by directing their spines towards the shadow above.

The acuity of vision was calculated using X-ray tomography and electron microscopy.

John Kirwan’s calculations show that of the 360 degrees surrounding the sea urchin an object must take up between 30 and 70 degrees for the sea urchin to see it. Humans only need an object to take up 0.02 degrees in order to detect it, making it clear that their eyesight is poor in comparison with human eyesight.

“However, this is still sufficient for the animal’s needs and behaviour. After all, it’s hardly poor eyesight for an animal with no eyes”, John Kirwan concludes.