Basket Stars

Each of your five arms develops arms of its own.  Those arms develop even smaller arms.  This repeats until your arms fill the gaps between them like a filigree. When you hold them out, they look like a fine mesh basket, which gives you your name: a Basket Star.

Beautiful, but mostly unseen, living in the deep cold waters of the northern hemisphere of the planet,  you crawl across the ocean depths, hiding during the day, and feeding during the night.  You are a pitiless hunter, grabbing krill - small swimming creatures -  in your basket and eating them.

Brittle Stars

A neat, small central body with serpentine arms reaching out from it enables you to move rapidly across the ocean floor, grabbing on to whatever you can to pull yourself around.  However, your relatively small body prevents you from eating anything sizeable, and so you remain a detritus feeder, scavenging your way around the deep seas of the world.  You are a Brittle Star.

Holothuroidea

Getting bigger, longer, musclier, and thicker, you have a long, efficient gut, and can get all the nutrients out of your food.  You live through several stages in your life now: tiny worm, little star, bigger star, until you become so thick and muscled that you tilt back and begin to look like a worm again, but a huge, thick worm, the size and shape of a common vegetable: you are a sea cucumber.

You still have radial symmetry, but unlike your sister species, your axis reverts back to horizontal, and you crawl or float or swim along with two 'legs' down, two to the sides. and one on top.  You secret a poison called holothurin which keeps you safe from many predators.  You mostly eat whatever detritus you find on the bottom, or whatever floats past you in the current.  Different species range from a few millimetres long to a whole metre long, and you live throughout the seas, although you are at your most dominant in the deep sea.

Asteroidea

The centre of your body is wide, giving you a large stomach, and your 'legs' are more triangular to fit around it. This shape gives rise to your popular name: the starfish.

You walk around on the ocean floor, in depths ranging from sunlit coral reefs down to abysmal depths, with your lightly armoured back protecting you from most species, your mouth facing downward, and no particular direction being 'forward', although some legs may be preferentially used.  Your legs have simple small eyes at each end.

With your powerful tube feet able to pry open bivalves by tiring out the muscles holding them closed, you become a predatory species, eating not just tiny bits of food like your recent ancestors, but whole small shellfish.

Some of you develop a neat trick of turning your mouth and stomach inside out and digesting whatever you press it against.  This enables you to consume even larger prey as your mouth no longer needs to be bigger than your prey!

Many of you develop a fascinating life cycle, where the young are male, but then turn into females after a certain age.  Some reproduce by budding, and some can regenerate their entire bodies from a single arm.  Truly, you are one of the most amazing creatures on the planet.

Echinoidea

You simply can't stop big jaws from crushing you.  But you can make it so unpleasant that these newly evolved predators will choose someone else.  The flat plates you already have become lumpy, and bumpy, and unpleasant to put in your mouth.  As time passes, those lumps and bumps get pointier and pointier, until you look like an explosion in a needle factory.

You are a sea urchin - a round-ish body covered in pointy spines.  You roam around the ocean from the tidal zone down to around three miles down, and very few creatures will eat you.  Those that do - crabs and lobsters, triggerfish, eels, humans -  avoid the need to bite down with soft mouthparts on spines by having special adaptations such as strong claws or bony mouths.  Or hammers.

Crinoid

You make lightweight armour from the calcium carbonate dissolved in sea water, but concentrate your energy on reproducing as fast as possible.

You float on the end of your 'stalk' or 'holdfast', a cup shaped flower, with both mouth and bum on top.  Many of you are eaten by creatures who have evolved jaws, but you grow fast enough to spread far and wide.  You spread like weeds across the seas of the prehistoric world, shedding so many thin calcium carbonate armour plates that entire chalk deposits, tens of metres thick, are entirely made of the broken up bodies of Crinoids.

Around 252 million years ago: the planet either gets hit by a huge space rock, or super-volcanoes explode, and the climate changes rapidly.  The seas change, becoming a little more acidic, and you can't make the plates of calcium-carbonate armour any more. Luckily, that's not crucial for your survival, and many of your species live on, adapting to become more flexible again.  Some of you become free-swimming as adults, with many flexible arms which float in the currents like grass in the wind, and inhabit both deep waters and reefs, where you are admired for your beautiful colours.

Blastozoa

You make thicker and thicker armour from the calcium carbonate dissolved in sea water.  It keeps you safe - for now.

You float on the end of your 'stalk' or 'holdfast', a small, five-sided ball, with a mouth on the top, and a bum on one side as far down as possible to take advantage of gravity.  On each of your sides, you grow an armour plate, and you filter feed in the shallower waters of the prehistoric world.  Many of you are eaten by creatures who have evolved jaws, but you grow fast enough to spread far and wide.  It's a good balance between the cost of armour and speed of reproduction.

We know of you now as one of the most common fossils of the Cambrian era, showing that there were uncountable billions of you.

Sadly, we can't know of you as a living species, because something quite bad happens around 252 million years ago: the planet either gets hit by a huge space rock, or super-volcanoes explode, and the climate changes rapidly.  The seas change, becoming a little more acidic, and you can't make the plates of calcium-carbonate armour any more.

You all die.  All the uncounted billions of you.

On the other hand, you're not alone, because around half of all life forms on the planet also die.  This is the Permian-Triassic extinction event, commonly known as The Great Dying.  It will take millions of years for the planet to recover.

Nemertea

Fight back!  Alright!  Let's do this.

You hide in the mud at the bottom of the sea, and wait.... when something yummy passes by, you turn your entire face inside out and stab them with a small, venom bearing, sting.  To eat them, you wrap your face around them and turn it back in again, drawing them inside, then go back to hiding in the mud.

Some of you develop long tails, anchoring you deep into the mud, where you stay for a lifetime.  Others swim or crawl on a slime trail between meals.  Hardly any of you are food for other animals.

It's a successful approach... if you like that sort of thing.

Annelida

Your body plan, so far, has been simple, like all worms.  Head, containing brain, mouth and sensory organs.  Thorax, containing lungs and other organs.  Abdomen, or tail, containing the gut.  The best muscles are around the thorax.  If you want more of those, there's only one effective way to do it: make another abdomen.  Then another.  And another.

Yes, you make segments of your body duplicate in their entirety: you become a segmented worm.  This turns out to be incredibly good.  You have redundancy in your organs, speed, and a nice big gut to get the most out of what you eat.

It's so successful that you develop into well over twenty thousand separate species (we just can't cover them all) including the earthworm and leech families.  You can swim, by undulating, wriggle through the soil or crawl across the top, using protrusions from the sides of your segments.  You are an enormously important aspect of soil health, and you are found just about everywhere that is not frozen or completely dry on the planet.

Lophophorata

That frilly mouth of yours we just mentioned?  It's pretty good.  One of the easiest ways to evolve is to do something you've already done - but even more.

You grow frills on your frills!

The super-frilly mouth is called a 'lophophore'.  You can hide away in the mud, and slide out your frilly frills and quietly eat whatever passes by.  As time passes you adopt many shapes, but all basically mud-hiding, filter-feeding, hard little worms.

Brachiopods

Growing a pedicle allows you to attach yourself to a convenient location when you find yourself in one, and become 'sessile' or permanently stuck to one place.  

You can stay there, opening your shell and filter feeding when it's convenient, and closing it again to hide inside when there is a predator around.  You release many, many tiny copies of yourself, which float around with the currents until, in their turn, they find a good place and stick themselves there, where they grow thicker and thicker shells and make more copies.  

Interestingly, since the Permian-Triassic extinction event, which didn't quite wipe you out, you haven't grown back as rapidly as a closely related species, the bivalve molluscs.  As a result, they appear to have dominated the upper, richer, waters, and you are mostly found at deeper locations.

It's a simple, relatively low cost way to make efficient use of free resources, and you are found in deep seas all over the world.

Hyoliths

You have become a Hyolith.  There were many species of hyoliths, but all took the form of a long conical or triangular shell, with a shell cap, and two helens which enabled them to stand up to feed with a crown shaped filter mouth.

You are first found in the early Cambrian period, over 500 million years ago.  However, your numbers appear to dwindle during the Permian period, up to 250 million years ago, possibly due to increasing acidity of the oceans making it hard to make enough shell material for your lifestyle.

At the end of the Permian period is the Permian-Triassic extinction event - the biggest extinction of species in the history of the Earth.  The cause of the P-T extinction is still debated, but we know that 90% of species didn't survive it.

You, already declining, were one of them.

Platyzoa

You remain a small worm, with an incomplete gut, which makes a living in the safe crevices of the world.

Many of you become flattened in order to maximise the rate at which oxygen travels through your skin, as you have no complex internal organs to pump blood or exchange gases.  Some of you acquire a common name of 'tape worm' as a result of this shape.

Some of the crevices you hide in are inside other animals, and you become a parasite, causing disease and slow death, as well as damaging the brains and reproductive capabilities of your host.  But what do you care?  You've evolved to survive, and this tactic is working well for you.

Enteropneusta

As you crawl along, you run the edge of your mouth along the bottom, taking in sand and dirt, and digesting anything useful which goes in with it.  Your long gut becomes longer and longer, to extract as much as possible from the detritus you find on the ocean floor.  Eventually, some of you become more than two metres long, all comprised of gut behind a muscular 'head' section.

For safety, you tend to burrow into the sea bottom, and then up again, making a U shape.  You stick your head out to feed, or stick your tail out to defecate.  When you live at the sea's edge, this makes makes characteristic 'casts' of sand at low tide.

The muscular head gives you a characteristic shape, which looks familiar and gives you your common name.  You are an acorn worm.

Pterobranchia

As you crawl along, you sometimes stop and rear your little wormy head up into the passing water.  A nice little plankton occasionally drifts into your mouth as a result.  A bigger mouth develops, which makes this more likely, and the edges of the mouth become frilly with cilia edgings, which wave in passing food.

You crawl less and less, and while you rear up your head, you dig your tail down to help you stay anchored.

When you create eggs, your larvae are free swimming until they find a good place to live, at which point they start to change shape, and excrete a glue which helps them stay still.  There you will stay for life, often in a small colony of similar, possibly even related, filter feeding worms called Pterobrachia.

Tardigrada

Instead of staying long and smooth like a worm, you develop bands around the body which give you a segmented shape.  Each segment develops a thicker part like a claw on each side.  Four segments are found to give the best results, three with two 'claws' each for walking, slowly, and one at the back which can be used to hold on to whatever you are living on.

You spread around the world, living in all sorts of conditions from the deep ocean to the high mountains.  You are almost unbelievably tough!  You can endure dehydration, radiation, temperatures only one degree above absolute zero and well above boiling point.

That 'slow walk' gives you your name: Tardigrades, commonly known as water bears.

That's as far as you can evolve here!  
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Nematoida

You stick with your worm shape, which is pretty well adapted, and spread around the world in massive numbers.  Your family, the Nematoid worms, eventually turn into thousands of different, but similar little worms, each adapted for a specific part of the global ecosystem.  Some live among the roots of trees, others are parasitic on a variety of hosts.

Possibly the most amazing thing about you is that you are everywhere.  There is no location on Earth where life is found where nematode worms are not found.

That's as far as you can evolve here!  

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Onychophora

You become a larger and faster worm.  By modern times, you can move at about 0.1 miles per hour, and have become an efficient hunter of insects and other small creatures.

You are still clearly a worm, because although you have what look like legs on the sides of your segments, they are only ever moved in pairs, so there is no real ‘walking’ gait.  You actually move much like an ancestral worm, but those paired ‘legs’ have gained the ability to flex slightly and actively grip on slippery surfaces.

You are a velvet worm.

That's as far as you can evolve here!  
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Hydrozoa

Many of you tiny cnidarians band together, to form what appears to be a single organism.  You are mostly, even in a group, quite tiny, but a few of you form colonies which are up to a couple of metres across.

Interestingly, many of your forms are not just a group acting together, but actually acting as a single organism, with the internal cavities joining into those of other individuals, in a conjoined form.

A few of you have given up on the 'normal' jellyfish form and spend only a tiny part of your life like that, having expanded the proportion of the larval stage to almost all of the time.  Medusa are single individuals which join to others and grow to form colonies.  As a result, only the single organisms can swim effectively and the colonies are either anchored to the sea bed, like fire corals, or floating freely with the wind to drive them, like Portugese Man o' War.

Some of you have adapted to form symbiotic relationships with crabs, and eat the crabs scraps in return for providing a stinging defence.  A few of you have even adapted to live in fresh water.

That's as far as you can evolve here!  
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Scyphozoa

You have become one of the 'true' jellyfish (although there is no particular reason to consider them more specifically jellyfishy than any one of the sister clades you would have reached with a slightly different choice).

You swim freely in the world's oceans, although you're not really strong enough to swim against any noticeable current.  You are fairly a passive consumer of plankton and very small creatures, such as fish and crustacean, which stray into your stinging, poisonous tentacles.

You have a two part lifecycle - the familiar free floating 'medusa' stage, and a larval stage which sits quietly on the sea bed, and either transforms into a medusa or buds one or more medusa off it.

You are found from the shallow warm waters of the world's shore-bound seas, to the dark, cold depths of the oceans, in hundred of species, limited only by your need to stay in salt water... for now.  

Who knows what changes the next mutation will bring?


That's as far as you can evolve here!  
You can go back to the start with the link above, or share what you became with the icons below.