Lyrarapax.

Lyrarapax is a new anomalocarid described on July 16, 2014. It’s the first known fossil of an anomalocarid that preserved the brain. The muscles of the swimming lobes are also preserved in the fossils. The study was published in the journal Nature, but I didn’t have access to the full article, only the abstract.

©lifebeforethedinosaurs.com

The fossils are from the Chengjiang biota of China and preserve the neural system and brain. The brain of Lyrarapax is very similar to a velvet worm’s brain. There have been some papers published speculating that anomolacarids might have been related to priapulids or certain other groups of worms. However, it was generally accepted that they were either arthropods or onychophorans (velvet worms), and these Lyrarapax fossils give really strong evidence for that.

©lifebeforethedinosaurs.com
My illustration of the head of Lyrarapax showing the brain and neural system.

Lyrarapax was only about 8cm long and did not have the fantail seen in some anomalocarids. Its claws were positioned horizontally, similar to Anomalocaris saron’s claws. In my opinion, Lyrarapax is similar to Amplectobelua, because the first pair of swimming lobes are very large, and the spine closest to the base of the claw is long and skinny. 

References:

Mysterious 500 Million-Year-Old Predators Are the Ancestors of Spiders

Brain structure resolves the segmental affinity of anomalocaridid appendages

Ctenoimbricata.

Ctenoimbricata (ten-oh-im-bri-kah-tuh) was an early echinoderm that looked a lot like a trilobite. It lived in the Cambrian, and the only two known specimens were found in Spain. It was described by researchers at the Natural History Museum of London and the University of Birmingham in 2012.

Ctenoimbricata was teardrop shaped, with many flat, triangular feeding appendages in the front. Like modern marine detritivores, it may have used its feeding appendages to put sand into its mouth, sort out the food from the sand, and spit out the excess sand. I think it probably would have eaten a small marine worm if it happened to catch one, like today's deep sea sea cucumbers do. 

©lifebeforethedinosaurs.com
Ctenoimbricata crawling on the sea floor

Ctenoimbricata was only 20 millimeters long, so it needed to have defenses. These were in the form of spines all over its body, similar to modern sea urchins. It was also probably slow, like modern echinoderms, and used tube feet to move around. It had hundreds, or maybe even thousands, of these tube feet, which are tiny, clear, gooey sticks, often with a suction cup-like device on the bottom used for moving around. 

©lifebeforethedinosaurs.com

Ctenoimbricata is a very important discovery because it is the oldest fossil that is definitely an echinoderm. The fossil was scanned and reconstructed, and the scientists found out it was bilaterally symmetrical, unlike other echinoderms, which have radial symmetry. This adds to the evidence that echinoderms and chordates may be related. 

©lifebeforethedinosaurs.com
Fossil of Ctenoimbricata

Thanks to Dr. Alien for first telling me about Ctenoimbricata!

References:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0038296

http://infaunalepiphany.wordpress.com/2012/06/09/from-worm-to-star-primitive-bilateral-echinoderms-from-the-cambrian-of-southern-europe/

http://emilyd47.blogspot.com/2012/06/ctenoimbricata.html

http://www.thisviewoflife.com/index.php/magazine/articles/bilateral-echinoderm-confirms-ancestry

Opabinia (Part 2)

Opabinia was a Cambrian invertebrate probably related to today's velvet worms. It was also related to Anomalocaris, which probably sometimes ate Opabinia. 


Opabinia's main food source was presumably worms, which were pulled out of their burrows by Opabinia's long proboscis, then torn up and eaten in its "pineapple ring"-shaped mouth located in a scoop on the underside of the creature's head. Another presumed food source of Opabinia was carcasses, especially of large animals such as Anomalocaris and Hurdia. 


One striking feature about Opabinia is that it possessed five huge eyes. Because of where Opabinia's eyes are positioned, it might have had 360 degree vision. It is thought that the eyes probably only detected motion. 


Opabinia swam by undulating the lobes on its sides. Each side possessed eleven lobes. For a burst of speed, Opabinia would have flicked its fins very quickly, similar to how a modern fish does a burst of speed. But Opabinia had a different fin arrangement than a modern fish. 


Opabinia was two to three inches long and probably swam along the bottom of the ocean. 

©lifebeforethedinosaurs.com
Opabinia searching for food.

Opabinia's closest relative was the Australian Myoscolex. Unlike Opabinia, it had no tail fan, and the eyes closest to the back had long stalks that curved backwards. So Myoscolex basically had eyes on the back of its head. And it needed to have eyes on the back of its head, because Anomalocaris, a top predator, was also present in Australia in the Cambrian, and it would have eaten Myoscolex. 


Opabinia was found on the other side of the world from Myoscolex, in British Columbia. 

©lifebeforethedinosaurs.com
Opabinia (top) compared with Myoscolex (below)

Opabinia also has modern relatives called Onychophora, or velvet worms. They live on land, mostly in Australia, and inhabit wet forests. They normally live in families inside logs in the day, but at night they come out to find food. There are usually up to fifteen velvet worms in a family. Velvet worms usually grow up to about 1-1/2 inches. 


Opabinia is actually quite similar to velvet worms if you look at it the right way. Because Opabinia is now thought to have had legs, if you take away all the fins and the proboscis, leave only two tiny eyes and add antennae, you get a velvet worm. 


Another modern relative to Opabinia is the tardigrade, which looks like a very short, stubby, microscopic velvet worm. One striking feature about the tardigrade is that it is nearly impossible to naturally kill, although it is probably very easy to intentionally kill by smushing it. It can be frozen, heated, and even put into space. Scientists put tardigrades into space without a spacesuit or a jar of air...and they survived!!!

©lifebeforethedinosaurs.com
A modern velvet worm on a forest floor. 

References:


http://rstb.royalsocietypublishing.org/content/271/910/1.short


http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=93&ref=i&


http://evolution.berkeley.edu/evolibrary/article/cambrian_06


http://paleobiology.si.edu/burgess/opabinia.html


http://dsc.discovery.com/news/2008/09/09/tardigrade-space.html


http://www.amazon.com/Space-Visual-Encyclopedia-DK-Publishing/dp/075666277X/ref=sr_1_3?ie=UTF8&qid=1342545454&sr=8-3&keywords=the+visual+encyclopedia+of+space

New research on Pikaia from Simon Conway Morris and Jean-Bernard Caron.

In Pikaia gracilens Walcott, a stem-group chordate from the Middle Cambrian of British Columbia, published online March 4, 2012, Simon Conway Morris and Jean-Bernard Caron confirmed that Pikaia was a chordate after all. They looked at the anatomy of 114 specimens of Pikaia (I thought there were only 16 known Pikaias!)and found myomeres, v-shaped blocks of skeletal tissue that are only found in chordates. The scientists also found evidence of a vascular system, and found that at least part of the alimentary canal was preserved in almost every specimen. 


Externally, Pikaia was mostly just a flattened, tie-shaped body tapering from a tiny head. It had tentacles on its head, two antennae, and a thin dorsal fin. 


What was first thought to be the notochord in Pikaia is now interpreted as a "dorsal organ," which was possibly hollow. This doesn't mean there's no notochord. Under this dorsal organ there is a thread of tissue that is now interpreted as the notochord and nerve chord. 


I've only read the abstract, but when I read the actual article I'll learn more information. 

Louisella.

Louisella was a priapulid worm that has been found in the Burgess Shale in British Columbia. It was one foot long, which meant it was the largest priapulid in the Burgess Shale. 

Louisella was a slender worm with feathery papillae running down the bottom of its body in two rows. These were possibly gills. It had a long proboscis on its head. Before the proboscis it had a ring of spikes pointing forward, which I think kind of looks like a crown. 

Like most Cambrian priapulids, Louisella was a predator, consuming small creatures such as hyoliths and swallowing them whole, front first. If Louisella swallowed hyoliths from the rear end, the spines of the hyolithid would get stuck in the worm's throat, possibly stab it, and prevent Louisella from eating any more hyoliths. Unlike its ferocious relative Ottoia, Louisella presumably was not as active, but it was almost certainly more active that Selkirkia, which would have found it hard to move in the first place.

© MARIANNE COLLINS

I believe that Louisella's large head spines prevented other priapulids from swallowing it while Louisella was small. The only priapulid that would have been likely to try to eat it would be Ottoia, which swallowed its prey head first. And if for some reason an Ottoia tried to swallow Louisella from the rear end, Louisella could just turn around and stab it. These spines would probably work against any other predator that tried to eat it. Even an arthropod would let Louisella go if it was stabbed in the right place, such as a joint or, as in the case of some arthropods, its softer underbelly. This is similar to the defense of Fieldia, which had a whole head covered in long, needle-like spines. But this is just my hypothesis about the use of the large spines on Louisella's head.

© SMITHSONIAN INSTITUTION – NATIONAL MUSEUM OF NATURAL HISTORY. PHOTOS: JEAN-BERNARD CARON

Some of the fossils of Louisella are very slender, while others are flatter and more sea cucumber-like. The holotype was one of these flattened specimens, which is what probably led Charles Doolittle Walcott to classify it as a holothurian, or sea cucumber. 

FOSSIL MALL

References:

http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=75&ref=i&

http://www.paleo.pan.pl/people/Dzik/Publications/PaleobiologyDzik.pdf

http://www.fossilmall.com/EDCOPE_Enterprises/invertebrates/invert12/invfossil-12.htm

The Crucible of Creation: The Burgess Shale and the Rise of Animals by Simon Conway Morris

http://en.wikipedia.org/wiki/Louisella

Siphusauctum.

Siphusauctum is a newly discovered animal from the Burgess Shale. It is one of the weirdest animals from the Burgess Shale ever found. Siphusauctum was described by Jean-Bernard Caron, Curator of Invertebrate Paleontology at the Royal Ontario Museum, and Lorna J. O'Brien from the Department of Ecology and Evolutionary Biology at the University of Toronto, and was just announced.

One of the most obvious things about Siphusauctum is how enigmatic it is. It looked like a ctenophore on a stalk. Some scientists believe that it is related to the mysterious Dinomischus. Siphusauctum and Dinomischus both have a stem and a round calyx, but they are actually very different. Dinomischus's calyx is more like a flower than a ctenophore.

© Marianne Collins

Siphusauctum had a two-layered stem and a holdfast at one end, which was probably used to anchor it to the sea floor. It presumably could draw its holdfast into the stem and move along the sea floor to find a new place to anchor itself.

Siphusauctum had a very simple gut, which was just a tube with a round part at the end, which was the stomach. It just sucked in water along with tiny creatures and plants, which were its food.

The size range for Siphusauctum is 19 mm to 223 mm. There are variable sizes for stems, holdfasts, and calyxes on different individuals of the species. One thing that stands out about it are the comb rows on its calyx, which resemble those of ctenophores. Although the two are unrelated, Siphusauctum has noticeable similarities with the ctenophores.

Siphusauctum are sometimes found in large clusters, suggesting that the animal lived in groups, like the possibly related Herpetogaster, also from the Burgess Shale. Its species name is S. gregarium because it was gregarious, meaning it lived in groups. Siphusauctum also resembles some crinoids, except crinoids had tentacles and Siphusauctum did not.

References:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029233

http://news.utoronto.ca/university-torontoroyal-ontario-museum-scientists-discover-unusual-tulip-creature

Protopriapulites.

Protopriapulites (pro-toe-pry-uh-pew-LITE-ees) was a priapulid worm that I think looked more like a peanut than a worm. It was about one centimeter long. Some fossils showing the gut full of mud indicate that Protopriapulites may have fed on detritus from the sea floor in the same way that the spiny Burgess Shale worm Fieldia did.

© Life Before the Dinosaurs 2012

Protopriapulites is known from the Chengjiang in China. It had a ball-shaped posterior, a head similar to that of Ottoia, and a proboscis similar to that of Fieldia. I believe that the ball-shaped posterior of Protopriapulites may have helped anchor it in its burrow, and if a predator tried to grab its head, it would not be able to pull the worm out of its burrow. So the predator would probably be discouraged and look for something else to eat. 

Protopriapulites was noticeably similar to Paleopriapulites, another peanut-shaped worm from the Chengjiang, except Protopriapulites had a spiral gut and Paleopriapulites did not.

Protopriapulites is a common species of priapulid worm in the Chengjiang.

Image from Fossil Mall

Protopriapulites is mentioned in the book The Cambrian Fossils of Chengjiang, China, which I received from Kamakanui, one of my readers. It is an amazing book mentioning some of the weirdest animals in the Chenjiang. It also has many obscure creatures which are hard to find on the internet, such as Protopriapulites. There is a whole section full of the enigmas of the Chengjiang, such as Facivermis. Each section has a certain phylum that the creatures mentioned in it belong to, in this case Protopriapulites would be listed under "priapulida." This book has tons of information on all these mysterious and obscure creatures.

References:

The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life, Blackwell Publishing, pg. 66 & 67.


http://www.fossilmall.com/EDCOPE_Enterprises/Chengjiang/chengjiangfossils91/chengjiangfossils-91.htm

Helmetia.

Helmetia was an unusual trilobite-like arthropod with eyes on the bottom of its head, and a broad, flat body. Having eyes on the bottom of its head would have blinded it if it crawled across the ocean floor, and its broad, flat body would have been buoyant and made it hard for Helmetia to get down to the sea floor in the first place, just like something flat will not sink in quicksand. Helmetia could reach lengths of about 19 cm, which was quite large for a Cambrian animal.

© SMITHSONIAN INSTITUTION – NATIONAL MUSEUM OF NATURAL HISTORY. PHOTO: JEAN-BERNARD CARON

Helmetia is obviously well-armored and large, so it probably didn't have too many predators. Large anomalocarids were the only animals big enough to even try to eat Helmetia. Helmetia had hard spines on the edges of its armor and its flat shape also would have made it hard for an anomalocarid to grip it. All its armor probably would have made Helmetia a slow swimmer, but this probably did not make it vulnerable.

Helmetia was presumably a filter feeder, feeding on plankton, bacteria, and other microscopic living things that floated around in the water column.


Fossils of Helmetia are extremely rare. They have been found in the Burgess Shale and were discovered by Charles Doolittle Walcott.

© Life Before the Dinosaurs 2012

References:

http://www.trilobites.info/triloclass.htm

http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=65&m=4&&ref=i#description

Odaraia.

Odaraia (oh-duh-RAY-uh) was a bizarre-looking creature that has been found only in the Burgess Shale. Charles Doolittle Walcott described this animal in 1912. The species name is Odaria alata, which is the only known species, except for a possible member of the genus from the Chengjiang in China, Odaraia? eurypetala. Although Odaraia  may have had four eyes, this is still disputed because the other two eyes on the fossils may have been something else.

Odaraia was first described as a crustacean, although it is now believed to have been a stem group arthropod. Odaraia presumably lived by swimming upside down in the water column as it searched for prey, which it sifted out of the water with its legs and ate. One of its most notable features was its three tail fins, which helped it stabilize in the water.

Odaraia had a large carapace that covered a fair amount of its body, including its legs. This meant that it would be impossible for Odaraia to walk on the bottom of the ocean, but it would be easy for it to swim.

References:

The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life, Blackwell Publishing, pg. 142. Many thanks to LBtD fan Kamakanui for this generous gift!

http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=89&ref=i&

http://en.wikipedia.org/wiki/Odaraia

Conodonta.

Conodonts were bizarre, fish-like probable chordates that may have resembled modern lampreys. They first evolved in the Cambrian, or possibly even the Precambrian, and died out in the Triassic-Jurassic extinction.

Conodonts were eel-shaped in form and most had large eyes, at least in comparison to the body. They had various toothy blades in the mouth to form what is known as "the conodont apparatus," which vaguely resembles the radula of a snail or slug.

Conodonts were probably capable of maintaining a cruising speed, but could not perform bursts of speed because their eel-like form would probably get them all tangled up. They would then be easy prey for any kind of predator trying to eat them. They probably swam in about the same style as an eel or loach. Although they had sharp teeth, they probably were not predators. Instead, they supposedly used "the conodont apparatus" as a sort of baleen to filter plankton from the water.

The largest conodont that has been found so far is Promissum, which reached lengths of 16 inches. Specimens of Promissum can be found in the Soom Shale of South Africa. Unlike most conodonts, Promissum had smaller eyes relative to body size. Promissum was about as long as an average house cat's body, without the head or tail.

The fist conodont specimens found were its individual toothy bars known as "conodont elements."

References:

http://www.ucl.ac.uk/GeolSci/micropal/conodont.html

http://en.wikipedia.org/wiki/Conodont

http://oceans1.csusb.edu/cdont_art.htm

Royal Ontario Museum Burgess Shale Fossil Gallery.

I first found The Royal Ontario Museum Burgess Shale Fossil Gallery before it was even finished being made, because I'm always using the internet to research fossils. The Royal Ontario Museum had to keep people from going to the website for a while because they were not done with it. But now they are done and it is amazing. 


I love that this fossil gallery tells you maximum size, supposed diet, abundance, classification, and morphology. It also has pictures of fossils, drawings, and even some videos. You can zoom in on the fossils and drawings to see them up close. At first it seems blurry, but then it clears and you can see amazing details. The Royal Ontario Museum Burgess Shale Fossil Gallery is the best place to find information and pictures of Burgess Shale fossils. The Gallery even features fossils that were discovered last year, in 2010. 

One of the most notably strange animals in the Burgess Shale that is featured in the ROM Fossil Gallery is Herpetogaster collinsi, which is weird. It had a flexible and extendible stalk, with a disc to anchor it to sponges. It had a sea cucumber-shaped body on top of the stalk. The body had thirteen segments, a circular mouth on top, and two branching tentacles on top of the head on either side of the mouth. Its maximum length was 48 mm. One amazing specimen of Herpetogaster collinsi shows many individual specimens attached to a single Vauxia gracilenta sponge. 

© ROYAL ONTARIO MUSEUM. PHOTOS: JEAN-BERNARD CARON

Another amazing animal in the ROM Fossil Gallery is Odontogriphus omalus. The fossil shown below preserves Odontogriphus grazing on mats of the cyanobacteria Morania. Odontogriphus omalus was an early slug-like mollusk, related to the more heavily armored Wiwaxia. 

© ROYAL ONTARIO MUSEUM. PHOTOS: JEAN-BERNARD CARON

A strange ctenophore that is featured in the ROM Fossil Gallery is Xanioascus canadensis. It looked like a balloon with eggs inside of it. It also had twenty-four comb rows, which are the rows of cilia that propel a ctenophore through the water. Modern ctenophores only have eight comb rows. Fossils of X. canadensis are usually found torn, suggesting that these ctenophores were very fragile and could be easily torn. One of the coolest things about the ROM Fossil Gallery is that they feature some very obscure animals and show a lot of information that most people cannot find anywhere else on the internet. Xanioascus canadensis is one of the very obscure creatures in the ROM Fossil Gallery. 

© MARIANNE COLLINS

I recommend that anyone searching for obscure Burgess Shale animals, or even non-obscure Burgess Shale animals, should go to the ROM Fossil Gallery. They have a lot of information, even the meaning of the names, which is something that I love to know. This Gallery has a wide range of Burgess Shale life, even cyanobacteria and algae. In my opinion, it's the best place to find information on Burgess Shale fossils. 


References:

http://burgess-shale.rom.on.ca/en/fossil-gallery/list-species.php
"Materials for this virtual exhibit – called 'The Burgess Shale' – were produced and/or compiled by Parks Canada (for the Parks Canada section) and the Royal Ontario Museum (for all other sections) for the Canadian Heritage Information Network (Virtual Museum of Canada program) for the purposes of providing the public with information about the Burgess Shale."

Anomalocaris (Part 2).

I've written about this animal before, but there is more information that I would like to talk about.

Anomalocaris was a very widely distributed Cambrian animal. Their remains have been found in at least China, Australia, Nevada, Pennsylvania, California, Georgia, Utah, Canada, and Greenland. Adults were normally about three feet long, but some could have grown up to six feet. Fossils of Anomalocaris canadensis show that it had a skinny head and long eye stalks, so it could have been able to turn its head and swivel its eyes while it was hunting for prey.

Some scientists believe that Anomalocaris ate trilobites. This evidence comes from Anomalocaris briggsi coprolites found in Australia, which contain pieces of trilobite exoskeletons, as well as trilobites with bite marks in them, which are found in many places. Some scientists don't believe that Anomalocaris normally ate trilobites because its mouth parts may not have been hard enough to penetrate trilobite exoskeletons. Anomalocaris mouth part fossils do not show any signs of being worn down by trilobite exoskeletons. But to some scientists this just points to the spines on the mouth parts being pliable but hard. So it's possible that Anomalocaris did still normally eat trilobites.

Anomalocaris fossils are most commonly found as disarticulated pieces, but well-preserved juveniles and some well-preserved adults are known.

Although A. canadensis had its claws curled up under its head. A. saron had its claws stretched out sideways in front of its face so they would have acted like scissors, where the spikes on one claw faced the spikes on the other claw. But there are other differences between the two species. A. saron had legs and cerci, while A. canadensis did not. But they did share the same basic structure. Some scientists believe Anomalocaris pennsylvanica was just a non-Canadian A. canadensis, but they might be different species.

References:

http://www.trilobites.info/anohome.html

http://en.wikipedia.org/wiki/Anomalocaris

http://whyevolutionistrue.wordpress.com/2010/11/17/a-new-anomalocaris-mystery/

Graptolithinia.

Graptolithinia is a class of shelled hemichordates that lived from the Cambrian to the Carboniferous. One of the first graptolites was called Chaunograptus, from the Burgess Shale. Chaunograptus made a living by hitching onto other animals like sponges and arthropods. Later graptolites, like Monograptus, had pelagic lifestyles and drifted with the ocean currents in the open sea. But one group of Graptolites, the dendroids, retained a benthic or a parasitic lifestyle.

The name graptolite means "writing on the rocks" in Greek, which refers to the fact that most graptolite fossils look like hieroglyphics. In life, some graptolites, like Monograptus, may have resembled hacksaw blades, where others, like Didymograptus, resembled pinking shears. There were hundreds, probably even thousands, of different forms of graptolites. The morphology of graptolites was very diverse.

The Ordovician graptolite Didymograptus.

Some graptolites were benthic, some were parasitic, some were pelagic, and there were many forms of graptolites living each of those lifestyles. Graptolites were hemichordates. They were not chordates, but they were very important in chordate evolution leading up to humans.

The Ordovician graptolite Phyllograptus. 

Graptolites are index fossils for the Ordovician and Silurian. Some graptolites are very common, like ammonites, which are also good index fossils. Most good index fossils are common, widely distributed, and from a limited time span. This helps scientists date rocks.

The Devonian graptolite Spirograptus. 

References:

http://www.ucmp.berkeley.edu/chordata/hemichordata.html

http://www.asoldasthehills.org/Graptolites.html

http://en.wikipedia.org/wiki/Graptolithinia

http://paleo.cortland.edu/tutorial/misc%20fossils/miscfossils.htm

Happy Halloween!

Diania cactiformus costume? Yes.

Agnostida.

Agnostid trilobites, or Agnostida, are bizarre trilobites that lived from the early Cambrian to the Ordovician mass extinction. In some Cambrian rocks, Agnostids are extremely common, and they are also spread all over the world in the fossil record. But in the Ordovician period, Agnostids become rare. But I believe they were probably still widespread.

A few Agnostid trilobite drawings of different species. [Artist unknown].

Most, but not all, Agnostids were blind, and they all were isopygous (meaning the pygidium, or tail, was the same size as cephalon, or head). Unlike other trilobites, Agnostids only had two or three thoracic segments, and like the order Nekaspida, which include Naraoia, some scientists do not believe that they are even trilobites. Instead they think that both these orders are more closely related to crustaceans than trilobites, but not stem group or crown group crustaceans.

Agnostid legs were unique among the appendages of trilobites, because most trilobites have legs similar to those of a pill bug. Agnostids have their own unique arrangement of legs and other appendages.

The ventral view of Agnostus, showing the legs and other appendages. 

Scientists disagree about whether Agnostids were benthic or pelagic. They seem to be benthic, because they are found with other benthic trilobites, and also have no eyes, which suggests that they would not be living at the surface where there is a lot of sunlight to help them see. But some scientists think they were pelagic because they are widespread, and usually pelagic animals can get to places more quickly and easily than benthic animals.

Some Agnostids could have been benthic predators that cannibalized and hunted in packs. Agnostids can commonly be found sheltered inside the remains of dead animals, including the abandoned tubes of the priapulid Selkirkia. Since the ones found in Selkirkia all have their head facing out of the tube, it indicates that they must have backed in for shelter and protection. Since the molted skins of Agnostids have not been found inside the tubes of Selkirkia, it means that they probably did not go into the tubes to molt.

References:

http://www.ucmp.berkeley.edu/arthropoda/trilobita/agnostida.html

http://www.trilobites.info/ordagnostida.htm

http://en.wikipedia.org/wiki/Agnostida

Skeemella.

Skeemella is a Cambrian animal that is found in Utah and is known from one specimen. The specimen has two halves: a posterior half and an anterior half. Although some scientists in China believe Skeemella is an arthropod, some American scientists believe it is a Vetulicolian.

Anterior half of Skeemella.
[Source: University of Kansas Division of Invertebrate Paleontology]

Skeemella had a long, skinny tail with two flukes that formed a paddle at the end of the tail. This picture shows Skeemella, the large elongate animal, and a group of the trilobite Peronopsis. The Peronopsis are probably searching for carcasses of Elrathia kingii, because they were some of the most common food sources that a scavenger like Peronopsis would be able to eat.

I believe that Skeemella may have been nocturnal, because its long tail would drag behind and in the day could be seen and grabbed by a predator. But in the nighttime, the big predators were either sluggish, inactive, or could not see well in the darkness, so Skeemella could be safe. But that's just my hypothesis.

My interpretation of Skeemella with a group of Paronopsis.

Skeemella had a tough carapace shaped like a fingernail, a beak-shaped mouth, no eyes, and two lobe-like extensions on the glob-like anterior part of the body.

Skeemella swimming slowly above the Cambrian sea floor in search of detritus or plankton.

References:

http://kumip.ku.edu/cambrianlife/Utah-Vetulicolians.html

http://www.fossilmuseum.net/Fossil_Sites/Chengjiang/Vetulicolia-Fossils.htm

Fieldia lanceolata.

Fieldia lanceolata is an odd species of Burgess Shale priapulid worm covered almost completely in spines. The longest spines were on Fieldia's head and looked like tiny spears. F. lanceolata was about 5 cm long and is the smallest Burgess Shale priapulid worm I know of. 

When Walcott found the first specimen of this worm, he thought it was an arthropod carapace. When he later found another specimen of Fieldia, he accidentally classified it as a different animal and called it "Ottoia minor." But the species "Ottoia minor" is now called Ancalagon minor, and is a totally different species than Fieldia, but is closely related in the priapulid stem group Archaeopriapulida. 

F. lanceolata had a short proboscis that may or may not have been been retractable or bendable like those of other priapulid worms. Its spines may have enabled it to push itself through the mud and burrow, or protect itself from predators. F. lanceolata devoured large amounts of sediment. We know that because some fossils of this worm have large amounts of mud in their gut. 

My interpretation of Fieldia lanceolata with mud in its gut.
© Life Before the Dinosaurs 2011

References:


http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=54&ref=i&


http://en.wikipedia.org/wiki/Fieldia_(worm)

Naraoia.

Naraoia (nuh-ROY-uh) was a soft-shelled trilobite-like animal with a posterior shield and an anterior shield. Walcott described Naraoia as a crustacean because of its large carapace. But now it is believed to be a trilobite-like animal because scientists know that it had soft parts under the carapace.

Even though Naraoia could swim for a very short period of time, its armor was too heavy to allow Naraoia to swim for very long. Naraoia probably crawled along the sea floor in search of prey. Some specimens of Naraoia show bite marks, so it was probably good prey for predators such as anomalocarids. Naraoia could be up to 4 cm long.

Click the image to see Naraoia crawl across the sea floor.

This fossil of N. compacta is one of the best preserved Burgess Shale fossils. It's a complete specimen and has well-preserved appendages. According to Stephen Jay Gould, it can be photographed unretouched, unlike most other Burgess Shale fossils.

References:

http://www.trilobites.info/naraoia.htm

http://evolution.berkeley.edu/evolibrary/article/_0/cambrian_17

http://paleobiology.si.edu/burgess/naraoia.html

http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=86&ref=i&

Wonderful Life, Stephen Jay Gould, pg. 87