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Wave Your Legs in the Air: conserving an elbow crab

 

Recently a beautiful little elbow crab was brought into the lab for conservation for remedial treatment. The crab was what we call a dried specimen, as it had been preserved (as the name suggests) by being dried out.

High and dry

Drying can be a very effective method of preservation. However, it does leave the resulting specimen both brittle and rigid. In the case of elbow crab, this fragility, combined with storage in its original unpadded box, meant the crab rattled around every time it got moved. This resulted in damage to four of the five legs on his (ed. note: I couldn't help it) right side.

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Pre-treatment crab (and associated body parts)

 

Conserving to preserve

Luckily for us, though the front three legs and the tip of the fourth leg had completely detached, all of the ‘missing’ legs were still present and accounted for in the wee crabby’s box. We can create replica legs or other parts of specimens when necessary, but it’s time-consuming and always a last resort.

One thing we always have to keep in mind during remedial treatment is that we’re not altering the specimen. We don’t want a researcher 75 years from now looking at our little buddy and thinking he or she has found a new species of crab because we’ve reattached a leg a bit wonky.


Starting off on the right feet

In this case, we had two detached legs of similar sizes. We examined the crab under a microscope to figure out which leg went in the second position and which went in the third position. This also allowed us to check how good the join would be between the body and his soon-to-be-reunited legs.


Once of the location and the exact orientation of each leg had been worked out, it was time to scrub in and start the surgery. The large front leg was reattached first. Attaching the smaller legs first would have prevented access to the broken joint of the front leg, making the whole process much more difficult.

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Strike a pose

 

The reattaching was done using a conservation-grade adhesive, applied under the microscope using a very fine-tipped paint brush. Although the adhesive selected provides a strong join when cured, it takes a couple of minutes to set. During that time each leg had to be held in exactly the right position or all our work would have been for naught.


We achieved this using gravity, some foam and a couple of entomology pins to help. As each leg was put in place, the body of the crab was carefully positioned using the foam and pins in such a way as to allow the leg to rest naturally in the correct position while the adhesive cured.

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Now just hold that for the next few hours, please

 

A successful operation

After several hours with its legs in a variety of positions, all of the crab’s detached pieces were securely back in place. The only thing left to do was to pass the little guy back to the Natural Science team for repacking in a box customised to stop any rattling and prevent further damage occurring. Once again, we farewell a patient back into the world, hopefully a bit more solid than when it came in.

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Two views of our little crab, reunited with his legs at last