Tully Monster

Colin

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Hi phil/serena

Never bred them on purpose but while i had them a baby or two would appear from time to time. Amazing that they literally just walk out of the female's back end and keep going.

The ones i worked with were from trinidad and were for a BBC film called Weird Nature. Agreed! Amazing animals!

They were once thought to be an annelid and then an arthropod and then the missing link between the two groups, now they are in a group of their own... Onychophorans.
 

Phil

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When people talk about 'living fossils' they usually mention the coelacanth for understandable reasons as these fish have barely changed for 100 million years or so. The onychophorans are a much better example; examples that are extremely similar are known from the Cambrian Burgess Shale (525mya approx) and recently have been found in the even earlier Chinese Chen-Jiang fauna. Peripatus, the Velvet worm, is the only modern representative, I think. (Please correct me if I am wrong Colin!)

I believe that it is currently thought that this bizarre group represents a survival of the stem group that led to the annelids and the arthropods, as Colin has mentioned, or possibly is a descendant of the earliest stem-arthropods. It is speculated that the jointed legs of subsequent arthropods evolved from the segmented soft lobopods of the earliest onychophorans. The slow hardening of the surfaces and the creation of joints allowed for greater control and specialisation of the limb, allowing the 'proper' arthropod to adapt to diversify and adapt to specialist niches, something the basic onychophoran could never do.

It's easy to forget that although creatures such as the Cambrian onychophoran Ayshaeia appear primitive, they were obviously a highly successful group, hence the survival of the modern Peripatus. The Burgess Shale being that incredible snap-shot of life in the Cambrian seas depicts Ayshaeia living alongside primitive arthropods such as trilobites; these fossils are clearly not representatives of the earliest proto-arthropods as the arthropods must have split from at an even earlier point in time.

Here are a couple of photos of Ayshaeia and Peripatus. Amazing to think that they are so far separated in time given their physical similarity:

Here is a lovely example of the Cambrian Aysheaia, compare with a photo of the modern Peripatus:

Ayshaeia

Peripatus
 
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