Such fascinating creatures! If you have missed it so far, don't miss it now - the two-part series by Mark H on DailyKos:
One day when I find some time, I'll have to write a long detailed post about the fascinating aspects of the circadian system and vision in the horseshoe crab (oh, some of which was done by Erik Herzog, so you know I like the stuff!).
As it happens, before dabbling in sea cucumbers and trekking around Africa, I spent a long time focusing on the elusive and charismatic limulus polyphemus. A species that's been around longer than dinosaurs.. it doesn't get much cooler than that!
Well - there is an idea for a blog post once you come back from Africa.