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Arthropods - the most diverse and successful animals in the history of this planet. ( Berkeley again - nice animated tour of the Arthropoda and the Cambrian Explosion ) You're probably carrying two parasitic varieties right now.

Since the Cambrian Explosion and after the mass carnage since, Earth has enjoyed the comprehensive mastery of it's exoskeletal overlords, that thrive happily in the mud of the ocean deep to high above the Himalayas.

Amongst the more memorable groups that didn't quite it make it to the present day, or even categorically into the arthropods, are the Lopododia - "Worms with legs" that included the ferocious carnivore Anomalocaris, with it toothy fangs and pineapple-ring mouth; and the freakish Opabinids. As far as we can tell, these were mostly sizable carnivores up to 2 metres long, (altho some such as this one appear to have been Planktivores) and left no descendants ( lucky for us - some of these things were positively Lovecraftian ).

Where they fit in the Ecdysozoan family tree is still open to considerable debate. Some authors suggest that Tardigrades and Onychophorans should be included in the Lobopodia, or that the anomalocarids and opabinids belong in their own group, the Terror Shrimps, away from the true Arthropods and their ancestors.

Whatever is eventually decided, they're fascinating, frightening, and not parasites. So on to the other memorable-but-extinct group.

Trilobites! A hugely successful group that were busily turning the oceans upside down between the mid-Cambrian 524 mya, and until they and practically everything else on the planet went belly-up in the Great Dying, 251 million years ago (altho they took various sharp kicks to the nads en route, too)

They seem to have started off as nearly blind soft-bodied creatures only recognised as trilobites when the Burgess Shales fossils were carefully taken apart to reveal the idiosyncratic details of trilobite hips, but promptly developed large and very complex eyes, and armour, and spikes, and quite possibly the ability to scream in abject terror about the same time Anomalocaris showed up.

They were highly diverse and record many lovely directions in evolution as they occupied every niche you can think of from big bottom-dwelling carnivores to fantastically delicate planktonic critters with huge eyes. But oddly enough, no obvious parasites, unless you agree with the only person to have ever proposed - altho given that his suggested species, Agnostus pisiformis , a tiny, blind , simplified creature, is so common is can form whole fossilisferous rock layers, this seems doubtful

For all your Trilobite needs, including Trilobite Of The Month, marsupial pouchs in their heads, and much more see S. M. Gon III's Guide to the Orders of Trilobites. Or Phil and Kaja Foglio's Girl Genius comic, where a trilobite in the family crest of Agatha Heterodyne. Also Trilobite-shaped Bose-Einstein Condensates, Flying Trilobites, and Trilobite Biccies.

Hmm. Another big chunk taken out of invertebrate evolution, and still no convincing parasites... Very well, I shall press on - in another post, coming soon to a screen near near you...


Dec. 3rd, 2007 10:39 pm (UTC)
Sam Gon III's site is kind of obsessively good.

Thanks for the link-love by the way.
The Flying Trilobite
Dec. 4th, 2007 02:14 am (UTC)
you're welcome, and yes it is :D

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