Elan IIe, tripod
|Feeling your way|
I like spider crabs, but they can be pretty difficult to get a detailed photo of, because of the habit this one is engaged in right in my tank. This common spider crab (Libinia emarginata) is busying itself with a fresh load of seaweed, using its mouth to shred the end into a mass of threads, then attaching the fragments to patches on the top of its shell that have fine Velcro-like hooks. This is done for camouflage, and one bright green piece can already be seen sticking well above its head. You can also see an anemone back there, but whether the crab placed it there on purpose, or whether the anemone picked the spot itself, I can't say. Anemones have been known to do that with many crab species.
But decked out like this, the pear-shaped spider crab can then forage for food deep in seaweed beds and be completely invisible to predators. In fact, I've found most by feel, despite the fact that they're usually decent-sized – this one is close to 5 cm (2 inches) across the body, extending well out to 15 cm with the legs extended. You're seeing the underside here as this one leans back, and the pincers it displays are good only for feeding, thus the defensive camouflage.