As part of the Life Photo Meme, I am posting this shot I took in Belize almost a year ago of a hermit crab, Coenobita clypeatus. My labmate, Alex (he is the one holding the crab), found him at South Water Caye's Marine Biological Station. The caption, etc. is from when I originally loaded the shot onto my Flickr account some time ago.
Although I refer to it as a male, the hermit crab could easily be a female, as there is no way to tell with them in the shell. The female gonopore is located under the 3rd pair of legs, securely locked away inside the shell. I will continue to refer to this one as "he" for the sake of continuity.
I seriously hope this little guy managed to find a better home shortly after this shot. Like most hermit crab species, C. clypeatus can change shells at the drop of a hat, though they often change back and forth "trying on" new shells a few times before settling in.
These crabs are generally nocturnal, hiding in leaf litter and in burrows during the day, and coming out in the evening to begin scavenging and climbing trees. They primarily eat fruit, dead plants and animals, and even feces. On the island we would find upwards of 20 hermit crabs dining on one cracked open coconut. They chirped and displayed dominance shoving behavior in these large communal dining events.
C. clypeatus can live to be in excess of thirty years old. They start life as fertilized eggs released to the ocean, where they develop as zoea through several molts before their gills are developed enough to extract oxygen from the air. Adult crabs remain on land for the remainder of their lives, but they do use ocean water as a source of salt during ecdysis.
Like many crabs, these hermit crabs have one claw, or cheliped, that is significantly larger than the other. Of the four pairs of walking legs, the rear most two are kept inside the shells to hold the shell, while the forward two pair of legs are used for walking.
The largest C. clypeatus we observed wore shells that were larger than my fist. One had a shell 8 inches from the outer lip of the aperture to the apex. These, however, are nothing compared to the 10 pound coconut crabs (Coenobeitidae birgus latro) from the Pacific, which can rip open a coconut with their large claws.
Here, then, is what the fellow above should look like: