How Silurian echinoderms ate

This October 2015 video from Utah State University in the USA is called What does the fossil record reveal about the evolution of Echinoderms?

By Laurel Hamers, 7:05pm, September 12, 2017:

Like sea stars, ancient echinoderms nibbled with tiny tube feet

Rare 430-million-year-old fossils preserve signs of these tentacle-like limbs

Sea stars and their relatives eat, breathe and scuttle around the seafloor with tiny tube feet. Now researchers have gotten their first-ever look at similar tentacle-like structures in an extinct group of these echinoderms.

It was suspected that the ancient marine invertebrates, called edrioasteroids, had tube feet. But a set of unusually well-preserved fossils from around 430 million years ago, described September 13 in Proceedings of the Royal Society B, provides proof.

Usually, when an echinoderm dies, “the tube feet are the first things that go,” says Colin Sumrall, a paleobiologist at the University of Tennessee, Knoxville who wasn’t part of the study. “The thing that’s so stunning is that they didn’t rot away.”

An abundance of soft-bodied creatures from the Silurian Period, which lasted from 443 to 416 million years ago, are preserved in a fossil bed in Herefordshire, England. The edrioasteroids found in this bed were probably buried alive by volcanic ash, entrapped before their soft tissues could break down, says study coauthor Derek Briggs, a paleontologist at Yale University. Decaying tissue then left a void that was filled in by minerals, which preserved the shape of the appendages.

Briggs and his collaborators slowly ground three fossils down, taking pictures layer-by-layer to build up a three-dimensional view. The specimens are a new genus and species, the analysis revealed. Unlike relatively flat sea stars and sand dollars, the species — dubbed Heropyrgus disterminus — had a conical body about 3 centimeters long. Its narrower end anchored in the seabed. The other end sported a set of five plates partially covering dozens of tube feet arranged in a pentagonal ring.

Today’s echinoderms use hydraulic pressure in a water vascular system to extend and retract their tube feet, which serve a variety of roles. The feet can help animals pull in tiny particles of food, filter water or gases, and even inch along the seafloor. Based on the placement of H. disterminus’s tube feet (and the fact that it’s stuck in one place), the animal probably used the appendages mostly for feeding and gas exchange, Briggs suggests. The fossils didn’t preserve the internal tubing that hooks up to the tube feet, but Briggs’ team thinks that it’s a series of canals arranged like spokes connected to a wheel hub.

Sumrall isn’t surprised that this edrioasteroid had tube feet. “It’s exactly what we would have expected,” he says. But all other preserved tube feet to date come from classes of echinoderms that still have living relatives today. Edrioasteroids are less closely related to modern echinoderms, so this find broadens the range of species that scientists know sported the structures.

H. disterminus does have a few surprises, though: Its tube feet are found in two sets, in an arrangement not seen in any other echinoderms. And while it has five-point symmetry in its fleshy top part (like most other echinoderms), that transitions to eight-point symmetry in its long, columnar body.

Sea stars sighted predators 79 million years ago: here.


Brittle stars fossils discovery in Australia

This video says about itself:

13 August 2017

Australia was a different place 275 million years ago – wild storms surged through icy seas, and marine animals lived a tenuous existence. But brittle stars had a survival strategy.

From the University of Cambridge in England:

Meadow of dancing brittle stars shows evolution at work

August 14, 2017

Newly-described fossil shows how brittle stars evolved in response to pressure from predators, and how an ‘evolutionary hangover’ managed to escape them.

Researchers have described a new species of brittle star, which are closely related to starfish, and showed how these sea creatures evolved in response to the rise of shell-crushing predators during the late Palaeozoic Era. The results, reported in the Journal of Systematic Palaeontology, also suggest that brittle stars evolved new traits before the largest mass extinction event in Earth’s history, and not after, as was the case with many other forms of life.

A fossilised ‘meadow’ of dancing brittle stars — frozen in time in the very spot that they lived — was found in Western Australia and dates from 275 million years ago. It contains several remarkably preserved ‘archaic’ brittle stars, a newly-described genus and species called Teleosaster creasyi. They are the last known complete brittle stars of their kind, an evolutionary hangover pushed to the margins of the world’s oceans by the threat from predators.

The researchers, from the University of Cambridge, suggest that while other species of brittle stars evolved in response to predators such as early forms of rays and crabs, these archaic forms simply moved to where the predators weren’t — namely the seas around Australia, which during the Palaeozoic era was pushed up against Antarctica. In these cold, predator-free waters, the archaic forms were able to grow much larger, and lived at the same time as the modern forms of brittle star, which still exist today.

Brittle stars consist of a central disc and five whip-like appendages, which are used for locomotion. They first appear in the fossil record about 500 million years ago, in the Ordovician Period, and today there are about 2,100 different species, mostly found in the deep ocean.

Early brittle stars were just that: brittle. During the Palaeozoic Era, when early shell-crushing predators first appeared, brittle stars made for easy prey. At this point, a split in the evolutionary tree appears to have occurred: the archaic, clunky brittle stars moved south to polar waters, while the modern form first began to emerge in response to the threat from predators, and was able to continue to live in the warmer waters closer to the equator. Both forms existed at the same time, but in different parts of the ocean.

“The threat from predation is an under-appreciated driver of evolutionary change,” said study co-author Dr Kenneth McNamara of Cambridge’s Department of Earth Sciences. “As more predators began to appear, the brittle stars started to evolve more flexible bodies, which enabled them to either burrow into the sediment, or to move more rapidly to escape.”

About 250 million years ago, the greatest mass extinction in Earth’s history — the Permian-Triassic extinction event, or the “Great Dying” — occurred. More than 90% of marine species and 70% of terrestrial species went extinct, and as a result, most surviving species underwent major evolutionary changes as a result.

“Brittle stars appear to have bucked this trend, however,” said co-author Dr Aaron Hunter, a visiting postdoctoral researcher in the Department of Earth Sciences. “They seem to have evolved before the Great Dying, into a form which we still see today.”

Meadows of brittle stars and other invertebrates such as sea urchins and starfish can still be seen today in the seas around Antarctica. As was the case during the Palaeozoic, the threat from predators is fairly low, although the warming of the Antarctic seas due to climate change has been linked to the recent arrival of armies of king crabs, which represent a real threat to these star-filled meadows.

Big sea cucumber in Egypt

This video says about itself:

This Bizarre Sea Creature is Snake-like and Has Tentacles | National Geographic

25 July 2017

Meet one of the world’s longest sea cucumbers, which has tentacles on its head.

A diver filmed this bizarre sea creature at the bottom of the Red Sea off Egypt. It’s likely its species is Synapta maculata—one of the world’s largest sea cucumbers. They can grow to be seven to ten feet long, and they filter feed by capturing floating organic matter with their feather-like tentacles.

Sea lily fossils discovery in World War I trenches

This 2015 video from the USA is called Everything About Crinoids

From Ohio State University in the USA:

Rock exposed in World War I trenches offers new fossil find

Sea lily ancestors spent youth hitchhiking around ancient oceans, discovery suggests

April 3, 2017

Summary: An unusual fossil find is giving scientists new ideas about how some of the earliest animals on Earth came to dominate the world’s oceans.

An international research team found 425-million-year-old fossilized remnants of juvenile crinoids, a distant ancestor of today’s sea lilies, encased in iron oxide and limestone in the Austrian Alps.

Researchers collected the rock from a formation on the border between Italy and Austria known as the Cardiola Formation, which was exposed in trenches dug during World War I.

Crinoids were abundant long ago, when they carpeted the sea floor. Most stalked crinoid fossils depict spindly, plantlike animals anchored to sea floor rocks, explained William Ausich, professor of earth sciences at The Ohio State University and co-author of the study in the open-access journal Geologica Acta.

Fossils of juvenile crinoids are rare, he said.

Rarer still is that these newly uncovered crinoids weren’t attached to rocks when they died. Whatever they were attached to during their young lives didn’t survive fossilization.

“The fossils indicate that they were either attached to objects floating in the water at the time, or attached to another bottom dweller that lacked preservable hard parts,” said Ausich said.

They might have clung to free-floating algae beds or swimming cephalopods, either of which could have carried them far away from where they formed as larvae.

Modern sea lilies reproduce by ejecting sperm and eggs into the water. Larvae grow into free-floating juvenile animals and eventually attach to the ocean bottom, where they grow to adulthood within 18 months.

At least, that’s what sea lilies do today. This fossil find suggests that their distant ancestors sometimes settled on objects that carried them far from home before they reached reproductive age.

“We now have important information about the behavior of these ancient organisms, and a clue as to why they had such a wide geographic distribution,” Ausich said.

With long, stem-like bodies topped with feathery fronds, crinoids resembled flowers, though the center of the “flower” was a mouth, and the “petals” were arms that captured plankton for food. At the other end of the creature was star-shaped organ called a holdfast, which gripped the seafloor.

While some of today’s sea lilies are able to detach their holdfasts from the seafloor and walk short distances on their arms, they don’t do it often. If their crinoid ancestors spent their entire adult lives similarly anchored to one spot, they couldn’t have spread worldwide without help.

Fossilized holdfasts are all that remain of the young crinoids uncovered in the Alps, and that’s not unusual, Ausich said.

“The hard part about studying the fossils that I study is that they need to be buried alive in order to be completely preserved,” he explained. “Crinoids and other echinoderms have a skeleton comprised of innumerable individual calcite plates held together by various connective soft tissues. These tissues begin to decompose within a day of an organism’s death.

“So, having only parts [of crinoids] rather than whole organisms is actually the norm — as frustrating as that may be.”

The sediment that eventually covered these young crinoids must have been rich in iron, because the holdfasts were preserved as minerals of iron oxide — and that detail is unusual, he added.

Today, the fossil holdfasts look like rusty star-shaped rings. The stars measure only 1 to 4 millimeters across, meaning they came from very young, post-larval juveniles.

The tiny fossils might have been hard to isolate from the surrounding rock, but researchers were able to take advantage of the presence of iron oxide to dissolve the limestone and pull the fossils from the resulting slurry with a magnet.

Researchers had actually collected rock samples from the Cardiola Formation long ago, Ausich said. The area contains abundant fossils, including ancient corals and trilobites. But only recently did anyone discover that these particular rock samples also contained the crinoid holdfasts.

Researchers are interested in crinoids not just because they’re part of Earth’s history, but because the various crinoid species were able to survive millions of years of climate changes to become the sea lilies we know today.

How baby starfish eat

This video from the USA says about itself:

15 November 2016

Eat, Prey, Swim: Dynamic vortex arrays created by starfish larvae

William Gilpin, Stanford University
Vivek N. Prakash, Stanford University
Manu Prakash, Stanford University

We show the surprising flow patterns created by a starfish larva, which churns the water around its body as it searches for algae, its primary food source. These vortices are unique to many invertebrates, which often struggle to obtain sufficient nutrients during the early stages of their development.

Our video shows how millions of years of evolution have allowed the larva to master fluid physics in order to solve the unique dilemma of feeding at the microscale. But this innovation comes with a price: the vortices decrease the animal’s swimming speed, and thus its ability to change locations and escape predators. By studying how physical forces shape the adaptation of simple animals, we hope to uncover the subtle manner in which physics shapes evolution.

From Science News:

Baby starfish whip up whirlpools to snag a meal

by Emily Conover

12:00pm, December 23, 2016

A baby starfish scoops up snacks by spinning miniature whirlpools. These vortices catch tasty algae and draw them close so the larva can slurp them up, scientists from Stanford University report December 19 in Nature Physics.

Before starfish take on their familiar shape, they freely swim ocean waters as millimeter-sized larvae. To swim around on the hunt for food, the larvae paddle the water with hairlike appendages called cilia. But, the scientists found, starfish larvae also adjust the orientation of these cilia to fine-tune their food-grabbing vortices.

Scientists studied larvae of the bat star (Patiria miniata), a starfish found on the U.S. Pacific coast, by observing their activities in seawater suffused with tiny beads that traced the flow of liquid. Too many swirls can slow a larva down, the scientists found, so the baby starfish adapts to the task at hand, creating fewer vortices while swimming and whipping up more of them when stopping to feed.

Sea cucumber biology, video

This video says about itself:

30 September 2016

In this entertaining short video, Jonathan explains the basic biology of sea cucumbers. A sea cucumber is a relative of starfish and sea urchins contained within the phylum Echinodermata.

Brittle stars of Terschelling island

This video, recorded on 25 July 2016 on Terschelling island in the Netherlands, shows brittle stars.