Friday Fellow: Crystalline crestfoot

by Piter Kehoma Boll

Even in the smallest pools or ponds of freshwater lost in a field, the diversity of lifeforms is amazing. Sadly, these environments are one of the most damaged of all ecosystems on earth and we probably have led many tiny species to extinction. Today’s fellow, however, is still alive, and its name is Lophopus crystallinus, or as I decided to call it, the crystalline crestfoot.

lophopus_crystallinus

A colony of Lophopus crystallinus. Photo by Natural History Museum, London.*

The crystalline crestfoot is member of the phylum Bryozoa, sometimes called moss animals. In fact, it was the first bryozoan to be described. As other bryozoans, the crystalline crestfoot lives as a colony of individuals attached to substracts in the lakes and ponds where they exist, which includes Europe and North America. The individuals are not fully independent and have specialized functions within the colony, thus acting as a single superorganism. As a general rule, bryozoans, including the crystalline crestfoot, are filter feeders, extracting particles and microalgae from water.

Despite being considerable tolerant to eutrophication (increase of  organic matter in water) and heavy metal pollution, the crystalline crestfoot is yet threatened by other forms of human impact, such as climate change and certainly by the destruction of its habitat. Once an abundant species, the crystalline crestfoot is now rare and declining. It is currently regarded as a threatened species in the United Kingdom and is the only bryozoan to have a Species Action Plan. Let’s hope we can find a way to avoid it to be wiped out from this world.

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ResearchBlogging.orgReferences:

Elia, A., Galarini, R., Martin Dörr, A., & Taticchi, M. (2007). Heavy metal contamination and antioxidant response of a freshwater bryozoan (Lophopus crystallinus Pall., Phylactolaemata). Ecotoxicology and Environmental Safety, 66 (2), 188-194 DOI: 10.1016/j.ecoenv.2005.12.004

Hill, S., Sayer, C., Hammond, P., Rimmer, V., Davidson, T., Hoare, D., Burgess, A., & Okamura, B. (2007). Are rare species rare or just overlooked? Assessing the distribution of the freshwater bryozoan, Lophopus crystallinusBiological Conservation, 135 (2), 223-234 DOI: 10.1016/j.biocon.2006.10.023

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Friday Fellow: Crawling Spider Alga

by Piter Kehoma Boll

The world of unicelular creatures includes fascinating species, some of which were already presented here. And today one more is coming, the marine phytoplanctonic amoeboid protist Chlorarachnion reptans, which again is a species without a common name, so I created one: crawling spider alga.

chlorarachnion_reptans

A plasmodium of the crawling spider alga Chlorarachnion reptans. Photo by Wikimedia user NEON.*

The crawling spider alga was dicovered in the Canary Islands in 1930. It is an amoeboid alga that forms plasmodia (multinucleated networks) of cells connected by thin strips of cytoplasm (reticulopodia). The reticulopodia are also used to capture prey (bacteria and smaller protists, especially algae) working kind of like a spider web. Additionally, the crawling spider alga has chloroplasts, so being able to conduct photosynthesis. It is, therefore, a mixotrophic organism, having more than one way of feeding.

The chloroplasts of the crawling spider alga, as well of other species in its group, called Chlorarachniophyceae, have four membrane layers and appears to have evolved from a green alga that was ingested and became an endosymbiont. As a result, the chloroplast of the crawling spider alga has two sets of DNA, one from the original chloroplast that came from an endosymbiotic cyanobacteria (located inside the inner membrane) and one of the green algae (between the two inner and the two outer membranes).

Although traditionally seen as a group of algae, the chlorarachniophytes are not closely related to the more “typical” algae, such as red, green, brown and golden algae or diatoms. They are actually relatives of other protists with thin net- or thread- like pseudopods, such as radiolarians and foraminifers, forming with them the group Rhizaria.

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ResearchBlogging.orgReferences:

AlgaeBase. Chlorarachnion reptans Geitler. Available at <http://www.algaebase.org/search/species/detail/?species_id=59340&gt;. Access on March 5, 2017.

EOL – Encyclopedia of Life. Chlorarachnion reptans. Available at <http://eol.org/pages/897235/overview&gt;. Access on March 5, 2017.

Hibberd, D., & Norris, R. (1984). Cytology and ultrastructure of Chlorarachnion reptans (Chlorarachniophyta divisio nova, Chlorarachniophyceae classis nova) Journal of Phycology, 20 (2), 310-330 DOI: 10.1111/j.0022-3646.1984.00310.x

Ludwig, M., & Gibbs, S. (1989). Evidence that the nucleomorphs of Chlorarachnion reptans (Chloraracnhiophyceae) are vestigial nuclei: morphology, division and DNA-DAPI fluorescence Journal of Phycology, 25 (2), 385-394 DOI: 10.1111/j.1529-8817.1989.tb00135.x

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Who came first? The comb or the sponge?

by Piter Kehoma Boll

The endless question is here again, but this time it appears to be settled. What animal group is the earliest of all? Who came first?

It is clear that there are five animal lineages that are usually regarded as monophyletic: sponges, placozoans, comb jellies, cnidarians and bilaterians. Let’s take a brief look at each of them:

Sponges (phylum Porifera) are always sessile, i.e., they do not move and are fixed to the substrate. They have a very simple anatomical structure. Their body is consisted of a kind of tube, having a large internal cavity and two layers of cells, an outer one and an inner one around the cavity. There are several small openings connecting the cavity to the outside, called pores, and one or more large cavities, called oscula (singular: osculum). Between the two cell layers there is a jelly-like mesohyl containing unspecialized cells, as well as the skeleton structures, including fibers of spongine and spicules of calcium carbonate or silica. Some species also secrete an outer calcium carbonate skeleton over which the organic part grows. Sponges lack muscles, nervous system, excretory system or any other kind of system. They simply live by beating the flagella of the choanocytes (the cells of the inner layer), creating a water flow entering through the pores and exiting through the osculum. The choanocytes capture organic particles in the water and ingest them by phagocytosis. All sponge cells can change from one type to another and migrate from one layer to another, so there are no true tissues.

porifera_body_structures_01

Body structures found in sponges. Picture by Philip Chalmers.*

Placozoans (phylum Placozoa) are even simpler than sponges, but they actually have true tissues. They are flat amoeboid organisms with two layers of epithelium, onde dorsal and one ventral, and a thin layer of stellate cells. The ventral cell layer is slightly concave and appears to be homologous to the endoderm (the “gut” layer) of other animals, while the upper layers is homologous to the ectoderm (the “skin” layer).

701px-trichoplax_adhaerens_photograph

Trichoplax adhaerens, the only species currently in the phylum Placozoa. Photo by Bernd Schierwater.**

Comb jellies (phylum Ctenophora) resemble jellyfishes, but a closer look reveals many differences. Externally they have an epidermis composed by two layers, an outer one that contains sensory cells, mucus-secreting cells and some specialized cells, like colloblasts that help capturing prey and cells containing multiple cilia used in locomotion, and an inner layer with a nerve net and muscle-like cells. They have a true mouth that leads to a pharynx and a stomach. From the stomach, a system os channels distribute the nutrients along the body. Oposite to the mouth there is a small anal pore that may excrete small unwanted particles, although most of the rejected material is expelled through the mouth. There is a layer of jelly-like material (mesoglea) between the gut and the epidermis.

bathocyroe_fosteri

The comb jelly Bathocyroe fosteri.

Cnidarians (phylum Cnidaria) have a structure similar to comb jellies, but not as complex. They also have an outer epidermis, but this is composed by a single layer of cells, and a sac-like gut surrounded by epthelial cells (gastrodermis), as well as a mesoglea between the two. Around the mouth there is one or two sets of tentacles. The most distinguishing feature of cnidarians is the presence of harpoon-like nettle cells, the cnidocytes, which are used as a defense mechanism and to help subdue prey.

800px-cross_section_jellyfish_en-svg

Body structure of a cnidarian (jellyfish). Picture by Mariana Ruiz Villarreal.

Bilaterians (clade Bilateria) includes all other animals. They are far more complex and are characterized by a bilateral body, cephalization (they have heads) and three main cell layers, the ectoderm, which originates the epidermis and the nervous system, the mesoderm, which give rise to muscles and blood cells, and the endoderm, which develops into the digestive and endocrine systems.

500px-bilaterian-plan-svg

Basic bilaterian structure.

Traditionally, sponges were always seen as the most primitive animals due to their lack of true tissues, muscular cells, nervous cells and all that stuff. However, some recent molecular studies have put the comb jellies as the most primitive animals. This was highly unexpected, as comb jellies are far more complex than sponges and placozoans, which would suggest that muscles and a nervous system evolved twice in the animal kingdom, or that sponges are some weird simplification of a more complex ancestor, which would be very hard to explain. The nervous system of comb jellies is indeed quite unusual, but not so much that it needs an independent origin.

However, now things appear to be settled. A study published this month on Current Biology by Simion et al. reconstructed a phylogenetic tree using 1719 genes of 97 animal species, and applying new and more congruent methods. With this more refined dataset, they recovered the classical reconstruction that puts sponges at the base of the animal tree, a more plausible scenario after all.

But why other studies have found comb jellies as the most basal group? Well, it seeems that comb jellies have unusually high substitution rates, meaning that their genes evolve faster. This leads to a problem called “long branch attraction” in phylogenetic reconstructions. As DNA has only four different nucleobases, namely adenine, guanine, cytosine and thymine, each one can only mutate into one of the other three. When mutations occur very often, they may go back to what they were in long lost ancestor, leading to misinterpretations in the evolutionary relationships. That seems to be what happens with comb jellies.

So, it seems that after all the sponge indeed came first.

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References and further reading:

Borowiec ML, Lee EK, Chiu JC, & Plachetzki DC 2015. Extracting phylogenetic signal and accounting for bias in whole-genome data sets supports the Ctenophora as sister to remaining Metazoa. BMC Genomics 16: 987. DOI: 10.1186/s12864-015-2146-4

Littlewood DTJ 2017. Animal Evolution: Last Word on Sponges-First? Current Biology 27: R259–R261. DOI: 10.1016/j.cub.2017.02.042

Simion P, Philippe H, Baurain D, Jager M, Richter DJ, Di Franco A, Roure B, Satoh N, Quéinnec É, Ereskovsky A, Lapébie P, Corre E, Delsuc F, King N, Wörheide G, & Manuel M 2017. A Large and Consistent Phylogenomic Dataset Supports Sponges as the Sister Group to All Other Animals. Current Biology 27: 958–967. DOI: 10.1016/j.cub.2017.02.031

Wallberg A, Thollesson M, Farris JS, & Jondelius U 2004. The phylogenetic position of the comb jellies (Ctenophora) and the importance of taxonomic sampling. Cladistics 20: 558–578. DOI: 10.1111/j.1096-0031.2004.00041.x
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Friday Fellow: Amphibian chytrid fungus

by Piter Kehoma Boll

Today I’m bringing you a species that is probably one of the most terrible ones to exist today, the amphibian chytrid fungus, Batrachochytrium dendrobatidis, also known simply as Bd.

batrachochytrium_dendrobatidis

Several sporangia of Batrachochytrium dendrobatidis (spherical structures) growing on a freshwater arthropod. Photo by AJ Cann.*

The amphibian chytrid fungus, as its name says, is a chytrid, a fungus of the division Chytridiomycota, which include microscopic species that usually feed by degrading chitin, keratin in other such materials. In the case of the amphibian chytrid fungus, it infects the skin of amphibians and feeds on it. It grows through the skin forming a network of rhizoids that originate spherical sporangia that contains spores.

The infection caused by the amphibian chytrid fungus is called chytridiomycosis. It causes a series of symptoms, including reddening of the skin, lethargy, convlusions, anorexia and excessive thickening and shedding of the skin. This thickening of the skin leads to problems in taking in nutrients, releasing toxins and even breathing, eventually leading to death.

chytridiomycosis

An individual of the species Atelopus limosus infected by the amphibian chytrid fungus. Photo by Brian Gratwicke.**

Since its discovery and naming in 1998, the amphibian chytrid fungus has devastated the populations of many amphibian species throughout the world. Some species, such as the golden toad and the Rabb’s fringe-limbed treefrog, were recently extinct by this terrible fungus. This whole drastic scenario is already considered one of the most severe examples of Holocene extinction. The reason for such a sudden increase in the infections is unknown, but it may be related to human impact on the environment.

We can only hope to find a way to reduce the spread of this nightmare to biodiversity.

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ResearchBlogging.org
References:

Fisher, M., Garner, T., & Walker, S. (2009). Global Emergence of Batrachochytrium dendrobatidis and Amphibian Chytridiomycosis in Space, Time, and Host Annual Review of Microbiology, 63 (1), 291-310 DOI: 10.1146/annurev.micro.091208.073435

Wikipedia. Batrachochytridium dendrobatidis. Available at <https://en.wikipedia.org/wiki/Batrachochytrium_dendrobatidis&gt;. Access on March 4, 2017.

Wikipedia. Chytridiomycosis. Available at <https://en.wikipedia.org/wiki/Chytridiomycosis&gt;. Access on March 4, 2017.

Wikipedia. Decline in amphibian populations. Available at <https://en.wikipedia.org/wiki/Decline_in_amphibian_populations&gt;. Access on March 4, 2017.

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Friday Fellow: Mexican Giant Horsetail

by Piter Kehoma Boll

If you are walking through the forest of Central America, you may end up finding something that at first you could think is a group of bamboos, plants growing as a cylindrical segmented stem that can reach up to 7 m in height, as seen in the picture below:

equisetum_myriochaetum

A group of bamboos? Not exactly. Photo by Alex LomasAlex Lomas.*

Those are not actually bamboos, though, but specimens of the largest species of horsetail that exists today, the Mexican giant horsetail, Equisetum myriochaetum. It can be found growing naturally from Peru to Mexico in areas of fertile soil, especially along water bodies such as streams and swamps.

As other horsetails, the Mexican giant horsetail has an erect and hollow stem with very narrow leaves growing in a whirl around the “joints” of the stem. The leaves are very simple, similar to those of more primitive plants such as the spikemosses and ground pines, but are thought to be a simplification of more complex leaves, as they are more closely related to the complex-leaved ferns.

More than only the largest horsetail in the world, the Mexican giant horsetail is an important medicinal plant in Mexican folk medicine, being used to treat kidney diseases and type 2 diabetes mellitus. And as in many other occasions, laboratory studies confirmed that water extracts from the aerial parts of E. myriochaetum do indeed reduce the blood glucose levels of type 2 diabetic patients without reducing their insulin levels. One more point to traditional medicine.

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ResearchBlogging.orgReferences:

EOL – Encyclopedia of Life. Equisetum myriochaetum. Available at <http://eol.org/pages/6069616/overview&gt;. Access on March 4, 2017.

Revilla, M., Andrade-Cetto, A., Islas, S., & Wiedenfeld, H. (2002). Hypoglycemic effect of Equisetum myriochaetum aerial parts on type 2 diabetic patients Journal of Ethnopharmacology, 81 (1), 117-120 DOI: 10.1016/S0378-8741(02)00053-3

Royal Botanic Garden Edinburgh. Equisetum myriochaetum. Available at <http://www.rbge.org.uk/the-gardens/plant-of-the-month/plant-profiles/equisetum-myriochaetum&gt;. Access on March 4, 2017.

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Shaking dinosaur hips and messing with their heads

by Piter Kehoma Boll

This week brought astonishing news regarding the phylogeny of dinosaurus, as you perhaps have heard or read. New anatomical evidences have completely rebuilt the basis of the dinosaur family tree and I’m here to explain a little bit of what happened.

As we all know, Dinosaurs include a great variety of beasts, from the meat-eating theropods to the long-necked sauropods and from the horned ceratopsians to the armored ankylosaurs, among many others.

largestdinosaursbysuborder_scale

Silhouette of a human compared to the largest known dinosaurs of each major group. Picture by Matt Martyniuk.*

For more than a century now, dinosaurus have been divided into two groups, called Ornithischia and Saurischia. Ornithischia (“bird-hipped”) includes dinosaurus whose pelvic bones are more similar to what is found in birds, with a pubis directed backward. Saurischia (“lizard-hipped”), on the other hand, have a pubis directed forward, as in reptiles in general. This grouped the theropods and the sauropods in the same group as Saurischia while other dinosaurus were grouped as Ornithischia. But birds are actually theropods, thus being lizard-hipped dinosaurus and not bird-hipped dinosaurus! Confusing, isn’t it? So let’s take a look at their hips:

Pelvic_bones

Comparison of the hips of a crocodile (Crocodylus), a sauropod (Diplodocus), a non-avian theropod (Tyrannosaurus), a bird (Apteryx), a thyreophoran (Stegosaurus), and an ornithopod (Iguanodon). Red = pubis; Blue = ischium; Yellow = ilium. Picture by myself, Piter K. Boll.**

As you can see, the primitive state, found in crocodiles, sauropods and early theropods, is a pubis pointing forward. A backward-pointing pubis evolved at least twice independently, both in more advanced theropods (such as birds) and the ornithischian dinosaurus. But could we be so certain that Tyrannosaurus and Diplodocus are more closely related to each other (forming a clade Saurischia) just because of their hips? Afterall, this is a primitive hip, so it is very unlikely to be a synapomorphy (a shared derived character). Nevertheless, it continued to be used as a character uniting sauropods and theropods.

A new paper published by Nature this week, however, showed new evidences that point to a different relationship of the groups. After a detailed analysis of the bone anatomy, Matthew G. Baron, David B. Norman and Paul M. Barrett have found 20 characters that unite theropods with ornithischians and not with sauropods. Among those we can mention the presence of a foramen (a hole) at the anterior region of the premaxillary bone that is inside the narial fossa (the depression of the bone that surrounds the nostril’s opening) and a sharp longitudinal ridge along the maxilla.

skulls

The skulls of both ornithischians and theropods (above) show an anterior premaxillary foramen in the narial fossa (shown in yellow) and and a sharp ridge on the maxilla (shown in green), as well as other characters that are not present in sauropodomorphs and herrerasaurids (below). Composition using original pictures by Carol Abraczinskas and Paul C. Sereno (Heterodontosaurus), Wikimedia user Ghedoghedo (Eoraptor and Herrerasaurus), and flickr user philosophygeek (Plateosaurus).**

In his blog Tetrapod Zoology, Dr. Darren Naish comments the new classification and points out some problems that arise with this new view. One of them is the fact that both theropods and sauropodomorphs have pneumatic (hollow) bones, while ornithischians do not. If the new phylogeny is closer to the truth, that means that pneumacity evolved twice independently or evolved once and was lost in ornithischians.

He also mentions that both ornithischians and theropods had hair-like or quill-like structures on their skin. In theropods this eventually led to feathers. Could this be another synapomorphy uniting these groups? Maybe… but when we think that pterosaurs also had “hairs”, one could also conclude that a “hairy” integumentary structure was already presented in the common ancestor of dinosaurus. In this case, perhaps, we only had not found it yet on sauropods. Now imagine a giant Argentinosaurus covered with feathers!

One concern that appeared with this new organization is whether sauropodomorphs would still be considered dinosaurs. The term “dinosaur” was coined by Richard Owen in 1842 to refer to the remains of the three genera known at the time, Iguanodon, Hylaeosaurus and Megalosaurus, the first two being ornithischians and the latter a theropod. As a consequence, the original definition of dinosaur did not include sauropods. Similarly, the modern phylogenetic definition of dinosaur was “the least inclusive clade containing Passer domesticus (the house sparrow) and Triceratops horridus“. In order to allow Brachiosaurus and his friends to continue sitting  with the dinosaurs, Baron et al. suggested to expand the definition to include Diplodocus carnegii. So, dinosaurus would be the least inclusive clade containing P. domesticusT. horridus and D. carnegii.

In this new family tree, the name Saurischia would still be used, but to refer only to the sauropodomorphs and some primitive carnivores, the herrerasaurids. The new clade formed by uniting theropods and ornithischians was proposed to be called Ornithoscelida (“bird-legged”), a name coined in 1870 to refer to the bird-like hindlimbs of both theropods and ornithopods (the subgroup of ornithischians that includes dinosaurs such as Iguanodon and the duck-billed dinosaurs).

What can we conclude with all that? Nothing will change if you are just a dinosaur enthusiast and do not care about what’s an ornithischian and a saurischian. Now if you are a phylogeny fan, as I am, you are used to sudden changes in the branches. Most fossils of basal dinosaurs are incomplete, thus increasing the problem to know how they are related to each other. Perhaps this new view will last, perhaps new evidence will change all over again the next week.

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ResearchBlogging.orgReferences and further reading:

Baron, M., Norman, D., & Barrett, P. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution Nature, 543 (7646), 501-506 DOI: 10.1038/nature21700

Naish, D. (2017). Ornithoscelida Rises: A New Family Tree for DinosaursTetrapod Zoology.

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Friday Fellow: Divergent Dinobryon

by Piter Kehoma Boll

Let’s return once more to the troublesome and neglected protists. This time I’m bringing you another tiny but beautiful alga, more precisely a golden alga. Its name is Dinobryon divergens and as usual there is no common name, so I invented one by simply translating the scientific name, thus I’ll call it the divergent dinobryon.

The divergent dinobryon is part of the class Chrysophyceae, commonly known as golden algae. Measuring about 50 µm in length, it lives in temperate lakes around the world and forms colonies composed of about 6 to 50 ovoid cells that are surrounded by a vase-like shell (lorica) of cellulose, as seen in the picture below.

dinobryon_divergens

A branching colony of Dinobryon divergens. The cells are clearly visible inside the lorica. Photo by Frank Fox.*

During colony formation, an original cell divides and one of the two daughter cells slides to the opening of the lorica and starts to construct a new one. It starts by creating the base of the lorica, which has a funnel shape and is attached to the inner wall of the original lorica. With further divisions, the colony starts to grow in a tree-like form. And the most interesting part is that the cells have two flagella and use them to swim, pulling the whole colony through the water.

As with other golden algae, the divergent dinobryon produces an internal siliceous structure that is globose, hollow and has a single opening connecting to the outside. This structure is called a statospore or stomatocyst and allows the cell to enter a resting state (cyst). The statospore is an important structure to help distinguish different species of golden algae.

The divergent dinobryon is a mixotrophic organism, meaning that it feeds by photosynthesis and by ingesting food too, especially bacteria. Kind of an interesting fellow, don’t you think?

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ResearchBlogging.orgReferences:

Franke, W., & Herth, W. (1973). Cell and lorica fine structure of the chrysomonad alga, Dinobryon sertularia Ehr. (Chrysophyceae) Archiv für Mikrobiologie, 91 (4), 323-344 DOI: 10.1007/BF00425052

Herth, W. (1979). Behaviour of the chrysoflagellate alga, Dinobryon divergens, during lorica formation Protoplasma, 100 (3-4), 345-351 DOI: 10.1007/BF01279321

Karim, A., & Round, F. (1967). Microfibrils in the lorica of the freshwater alga Dinobryon New Phytologist, 66 (3), 409-412 DOI: 10.1111/j.1469-8137.1967.tb06020.x

Sandgren, C. (1981). Characteristics of sexual and asexual resting cyst (statospore) formation in Dinobryon cylindricum Imhof (Chrysophyta) Journal of Phycology, 17 (2), 199-210 DOI: 10.1111/j.1529-8817.1981.tb00840.x

Sheath, R., Hellebust, J., & Sawa, T. (1975). The statospore of Dinobryon divergens Imhof: Formation and germination in a subarctic lake Journal of Phycology, 11 (2), 131-138 DOI: 10.1111/j.1529-8817.1975.tb02760.x

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