CULTURAL QA 01-2024-06 Q What arethe major animal phyla and the characteristics of each? I'm looking for 10 different phyla.
A Gary Meaney,author of Zoology's Greatest Mystery (2022)6h For those who aren’t familiar with the term, we divide the animal kingdom into very broad groups called phyla.A single phylum can contain an extraordinary diversity of species - we, Homosapiens, share ours with beings that look more like aliens than animals. Evenstill, there are a lot more than ten of them. Believe it or not, we currently recognise over 30 living animal phyla! Let’s meet them all. 1. As humans, ourphylum is called the Chordates. This group includes the vast majority of “familiar” animals- our fellow mammals, as well as reptiles, birds, and amphibians… all the large land-dwellingcreatures of the Earth. All the fish too - both the bony variety, andthose whose skeletons are made of cartilage, like sharks. People often use the word“vertebrates” interchangeably with “chordates”, butthis isn’t entirely true. The animals I just mentioned represent the vertebrates, asthey all have a backbone. However, there are other chordates which don’t! Instead, these creatures have a primitive rodof elastic material called a notochord. Think of it as a precursor tothe backbone - our ancient ancestors had one, hundreds of millions of yearsago. There are two groupsof non-vertebrate chordates alive today. The former are incredibly strange, jelly-like animals, whichroot themselves to the seabed and siphon water through their bodies, filteringtheir tiny plankton food from it. I could never do their weirdness justice inthis short paragraph, but I wrote a full answer on them a while ago. The latter - the lancelets - are also found in the oceans. They have a verysimple body plan, with a sleek blade-like form, a tail fin for swimming, and amouth full of little tentacles. It’s likely that the first ever chordates toevolve, more than half a billion years ago, resembled lancelets! 2 The second phylumwe’ll meet is called the Echinoderms. Together with another which I’llmention in a moment, theseguys are the closest cousins of the chordates, though you wouldn’t think itfrom looking at them! This group includes starfish, their more slendercousins the brittle stars, as well as sea urchins, sea cucumbers and themesmerising feather stars, pictured third below. Echinoderms are very unique because of their symmetry.Most animals, including us, have what’s called bilateral symmetry- the left sideof their body is more or less a mirror image of the right side. Think of astarfish, however; it instead has evolved “pentaradial” symmetry. Its body canbe divided into five identical parts arranged around a central axis. The sameis true for all echinoderms! 3 There is a very obscure phylum which representsthe closest relatives of the echinoderms:the Hemichordates. Some, termed acorn worms, live inside burrows in sedimentson the sea floor. They are rather slimy creatures which often bear anuncomfortable resemblance to certain human anatomy. An acorn worm is picturedbelow. Others live together in colonies, clusters of manyfilter-feeding individuals, whose tentacles sift through the water for food. Hemichordates get their namefrom the supportive rod-like structure found within them - it’s almostlike the notochord or backbone which defines us chordates. As we continue, the animals we’ll to meet are even moregenetically distant to us humans, and in many cases, more bizarre. 4 First, though, let’s check in with another set offamiliar faces - the Arthropods. The diversity of arthropods cannot beunderstated - out of the 1.5 million animal species we have classified, theyalone account for more than a million, and there are doubtless many millionsmore waiting to be discovered. With this phylum,we’re talking about insects, spiders, scorpions, crabs, lobsters, barnacles,millipedes, centipedes and so so much more. They’ve conquered every environment on Earth andrange in size from utterly microscopic plankton to the gigantic Japanese spidercrab. The exoskeleton - an armour plating made of tough chitin - is what definesthe arthropods. 5 The famous Tardigradesare another phylum- though they might look a bit likearthropods, they have their own distinct group. Also known as water bears, they have eight legs, andtypically grow to just half a millimetre in length. They can be foundeverywhere - mosses, soil, leafy forest floors, coastal sands, riverbeds,sediments at the bottom of the sea. Indeed, they are notorious for theirmind-blowing ability to withstand just about every set of conditions scientiststhrow at them. Some tardigrades cansurvive temperatures of -273 degrees Celsius - yes, absolute zero. Other species have endured 150degrees Celsius! Pressures that would crumple most animals like a cokecan? No problem. Radiation sufficient to obliterate a human? That’s nothing. These water bears arepractically indestructible! 6 Next we come to the Velvet Worms, who are the only animalphylum that is found only on land, never in the sea. There are “only” about two hundredspecies, all of which roam tropical or subtropical regions of the world. Velvetworms have loads of little stubby legs - up to 86 - each one tipped with a tinypair of claws. Up close, they almost look cute! Don’t get on their bad side, though. When threatened, velvet worms spray twin streamsof slime from their face! This sticky substance can also be used to trapunsuspecting prey. 7 Now, the ubiquitous Nematodes, alsoknown as roundworms. According to the latest estimates, there may be a million species ofnematodes wriggling around this planet. As is the case for the arthropods andtardigrades, it seems there is no environment roundworms can’t conquer -they’ve even been found several kilometres below the Earth’s surface! Even more incredibly, it’s thought that there are about 500trillion of them alive. That accounts for about 8 in every 10 individualanimals in the world! This leads to the unexpected factoid that the averagenumber of legs for an animal is about zero. Roundworm expert Nathan Cobb put itbest: “In short, if all the matter inthe universe except the nematodes were swept away, our world would still bedimly recognizable, and if, as disembodied spirits, we could then investigateit, we should find its mountains, hills, vales, rivers, lakes, and oceansrepresented by a film of nematodes.” 8 The Nematomorphs, or horsehair worms, lookvery similar to nematodes at first glance, but some fundamental differencesearn them a phylum of their own. Adult horsehair worms live in streams, puddles, ponds and the like, buttheir larvae (babies) are parasites of insects, especially grasshoppers. Thus, they spend thefirst phase of their life inside an insect host, before taking on theirfree-swimming final form and emerging. The larvae often manipulate their hosts in terrifying ways.One species, for example, is a parasite of praying mantises, living insidetheir eyes. Amazingly, it can alter the cells in the mantis’ eyes such that itbecomes attracted to horizontally polarised light, a specific form of lightthat reflects off the surface of water bodies. Zombie-like, the bug makes abeeline for the water and drowns, allowing the nematomorph to complete its lifecycle. 9 Now for a bunch moreobscure small phyla. The Mud Dragons might have the coolestname of any animal phylum hands down, though admittedly it sells them as slightly more exciting creatures thanthey actually are. Mud dragons rarely exceed a millimetre in length, and have asegmented body covered in spines, but no legs. As their name suggests, they dwell in the mud at thebottom of the ocean. Back in the Cambrian times, about half a billion years ago,the early mud dragons grew far larger than their modern counterparts. We now go from a cool name to a funny name - however, Ihesitate to write it here, lest Quora flag my answer as inappropriate! You canprobably guess it from the picture, in any case. 10 For the time being, I will use the phylum’smore scientific name, the Priapulids. As another clue, this name comesfrom Priapus, the Greek god of fertility. Like their aforementioned cousins the mud dragons, priapulids live in the siltbeneath shallow waters. They can be a lot bigger though, at up to 40 centimetres in length. 11 Let’s now meet the mostmysterious animal phylum of all: the Loriciferans. To date, we’ve described about 40 species, the first of which was only found inthe ‘80s! They evaded discovery for so long due to their unique lifestyle:they cement themselves to grains of gravel on the seafloor, seldom ever comingloose from their substrate. They’retiny, too, though beautiful under the microscope Just a couple years ago, a species was discovered livinginside a pool of brine (exceptionally salty seawater) that had gathered at the bottom of a deep basin in theMediterranean Sea. This environment is completely devoid of oxygen, andis one of the few ecosystems on Earth that is not based on energy from the Sun,and photosynthesis. This makes loriciferans the only multi-celled organisms inthe world that can spend their entire lives without oxygen! 12 We now return toanother well-known phylum, the Molluscs. Mollusc diversity is breathtaking - the group includessquids, octopuses, cuttlefish, snails, slugs, clams, and a host of other slimy wonders. One of their distinguishingfeatures is an organ called the radula - essentially, a long tongue covered inthousands of microscopic razor-sharp teeth, which emerges from themouth during feeding. Almost all molluscs have one! Among their ranks, they boast the largest invertebrate onEarth: the colossal squid,which may weigh up to 700 kg, and measures ten metres in length. Some ofits relatives - octopuses, most famously - also seem to be the world’s mostintelligent invertebrates! Molluscs are cousins to various phyla which aren’t quite asflashy or interesting to the layperson, so I’ll do a quick whirlwind tour ofthem. 13 You’ve got the Brachiopods,which look a bit like clams superficially. Look closely at the photo below and you’ll see thecreature’s so-called lophophore: a U-shaped arrangement of countless hairs inside the “mouth”.These hairs are wiggling constantly, so as to keep water circulating throughthe body. The Horseshoe Wormsalso have a lophophore, but this time the crown of tentacle hairs is circular, and it’s out ondisplay, not enclosed within any kind of shell. They use this organ tofilter-feed; it’s almost like a fishing net, passively catching tiny morsels offood from the passing sea water. Some horseshoe worms have striking vividcolours! 14 Few animals look morealien than the Entoprocts. These minuscule beings live in the sea, but don’tswim; rather, they stay rooted to a stable surface. The entoproct body is shapedlike a wine glass, with a central stem at the base and a ring of tentaclesforming a “cup”. Theyare hermaphrodites - there are no distinct males or females, that is - andfascinatingly they reproduce via cloning! Most species live in vast colonies of countless individuals,which are all fused to each other, connected by common tubes called stolons.Truly bizarre creatures! 15 The closely related Bryozoansoften have a similar colonial lifestyle. A bryozoan colony acts almost as a massive super-organism,with each individual acting almost as a cell. Just like cells, the colonymembers even specialise - some exist solely for feeding, others for structuralsupport, others for snapping at predators, others still for reproduction.Animals like these really challenge our definitions of what an organism is -and what it isn’t. 16 The last of thesemollusc-adjacent phyla is the Ribbon Worms. Among their defining characteristicsis a rather gruesome weapon: a slimy proboscis, which can be launched out ofthe head, and inject venom into poor unsuspecting prey. Ribbon worms are extremely elastic - they canstretch out to ten times their resting size, or triple in thickness atwill! In fact, you may be surprised to hear that the longestanimal in the world is a ribbon worm! One specimen was recorded atan utterly gigantic 54metres in length,which is almost double that of the largest blue whale. 17 Continuing with our wormy theme, we arrive at the Annelids. A lot of the more “popular” worms,if they can be called that, belong to this phylum - including the iconicearthworms. Leeches alsofall under the annelid category. They all share one crucialcharacteristic - a segmented body. 18 I myself am partial to the bristleworms,a diverse subset of the annelids. Each segment along their lengthbears a pair of paddles, termed parapodia, which help them get around. A lot ofthe bristleworm species you’ll find in the deep sea are shockingly beautiful,and often bioluminiscent. Look at this one! 19 The Cycliophores are a strong candidatefor the oddest animal phylum out there. In1995, zoologists discovered a microscopic marine species that was so utterlydifferent from anything previously known that it had to be assigned to a wholenew phylum of its own. To this date we only know of a pitiful threespecies, all of which are similar enough to each other to be in the same genus. The way cycliophores reproduce is so mind-bendingly bizarrethat I’ll need to write a full answer about it to do it justice. As a teaser, just know that atone point in its life cycle, the animal is reduced to just 47 individual cells!There is really nothing like this phylum elsewhere in nature. 19 Moving on, we have the Flatworms. These animals are extremely simple in anatomy compared tothe ones we’ve already met: they have no real circulatory or respiratory system. Instead, oxygen just diffusesthrough the body from cell to cell. To facilitate this, their bodies arepaper-thin - flatworms are, indeed, flat worms. Though many are microscopic, the larger flatworm speciesoften have bright colours (advertising their poisonous nature to would-bepredators), and can be quite pretty! 20 The Hairybellies just about beat the muddragons for the title of best-named animal phylum. The title refers to the many cilia(hair-like projections) which line their body and allow them to swim throughthe water. Hairybelliesare similar to flatworms in many respects and can usually only be seenwith a microscope. 21 There is another flatworm-like phylum - the Mesozoans -but in the nicestway possible, they really just aren’t particularly remarkable creatures, so Iwill sadly omit them for brevity. 22 Instead, let’s progress to the Rotifers, also known as wheel animals. Like many of the phyla we’ve coveredso far, they are abundant, aquatic, and microscopic. Thanks to the crown oftendrils which projects from their mouth, they’re unmistakeable.They can lookpretty scary up close! Animals in some phylarelated to the rotifers possess surprisingly complex jaws, made of chitin. Such an advanced feature is quiteunexpected in these relatively primitive animals! 22 and 23 These two phyla are referred to as the (aptlynamed) Jaw Worms, theArrow Worms and the Micrognathozoans. That last one is a mouthful!Here’s a close-up of those chitinous chompers. 24 For another mouthful of a name, take the Xenocoelamorphs. That’s just a few letters away frombeing a James Cameron movie monster! These creatures are far less scary, thatbeing said. They don’t really have any true organs or anything, they’re almostjust living blobs. That said, we’re only just beginning to get to the trulyprimitive and alien animals. 25 It’s time for the Cnidarians. The most recognisable members of thisphylum are without doubt the jellyfish,famed for their anatomical simplicity. Sea anemones and corals are also part of this group.They all share a fundamental trait: cnidocytes, specially adapted cells whichcan release a venomous harpoon when triggered. This is what gives a jellyfish its sting! 26 The most interesting cnidarians, to me, are the siphonophores, colonial creatures which team up in their thousands to forma giant super-organism. Believe it or not, the iconic Portuguese man o’ war isnot a single creature, but a colony of them working together. Some siphonophore colonies cangrow to be over 40 metres long! They truly look like something from analien world: 27 The simplest animals on Earth are the Placozoans. Really, they are more like amoebas than animals. They have no defined shape, nobody parts of any kind. They multiply via budding or fission, never withsexual reproduction. This is animal life in its most basic form. Despite this, we still haven’t quite reached the base ofthe animal family tree. In a genetic sense, there are more phyla that are evenmore primitive. 28 Our penultimate phylum:the hauntingly beautiful Comb Jellies. Often confused with jellyfish, these strange beasts have ahollow, translucent body, lined with “combs” of cilia which flutter to propelthem along. Some species have a pair of long tentacles trailing behindthem, while others are bioluminescent. They can be up to 1.5 metres in diameter! 29 Now, we finally arriveat the most primitive and ancient of all living animals: the Sponges. Theydo not move, and have no real organ systems to speak of. Their survival is based on themaintenance of a constant flow of water through them, water which they filterfor tasty plankton. It is possible thatsponges have been around for well over 600 million years! They are old in another sense, too- the giant volcano sponge of Antarctica is the world’s longest-lived animal.Some living specimens are estimated to be a staggering 15,000 years of age! With that, we conclude our epic journey through 31 different animal realms. If you stuck around this long, Isincerely thank you! I know that most of these species aren’t as glamorous tothose who aren’t animal obsessives the way I am, so I hope this was somewhatinteresting. I hope 2024 is treating you well, and as always, have a great day! My note- Most of us would have studied in pre-degree orintermediate about different phylam.Zoology Main would have studied more. For me it was an interesting reading. TheQA is from Quora. Icould number only 29. 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