Photo of the Week: August 22, 2011

Hi Gang!

I am returning to my recent trip to the Philippines with Captain Steve and the gang for this week’ POTW. It is a photograph of a spotted porcelain crab (aka spotted anemone porcelain crab) that is actively feeding.

As is the case with all porcelain crabs, spotted porcelain crabs feed by filtering organic particles and plankton out of the water column with elaborate, feathery-looking structures known as setae. The crabs wave their setae about in the water column, trap any food particles that they can, and then draw the setae and the food into their mouth. It is the fact that the spotted porcelain crab is actively feeding by using its setae to filter food out of the water column, and the fcat that you can see the setae in the image, that makes the picture special to me. Spotted porcelain crabs also feed on detritus on the sea floor.

Described in the family Porcellanidae, porcelain crabs are more closely related to squat lobsters (not “true” lobsters) and hermit crabs than they are to most of the creatures that most divers tend to think of as crabs. It is generally believed that despite their different origins, over time porcelain crabs evolved into animals that look a lot like the animals we usually think of as “true crabs”.

Of course, taxonomists are quick to point out that there is no such thing as a “false crab”. The takeaway message is that while porcelain crabs are decapods (ten-legged crustaceans), they are more closely related to hermit crabs and squat lobsters than they are to creatures such as sheep or king crabs. 

Porcelain crabs are equipped with two claws that are used in competition over territory and in defense. Their big claws relative to body size give these formidable looking creatures a menacing appearance in some cases, but the use of the word porcelain in the common name is derived from the fact that porcelain crabs are comparatively fragile creatures that are quick to shed, or “shatter”, a limb when they are attacked. In many cases the lost body parts can be re-grown over the period of several molts.

The spotted porcelain crab commonly associates with anemones. The crab nestles amongst the anemone’s tentacles. When feeling threatened the crab will quickly retreat under the anemone or into a fold in the body of the anemone. If necessary, the crab will use its claws to grab the anemone and pull folds of the anemone over its own body to hide and gain protection from the stinging tentacles of the anemone.

I created this week’s POTW image with a Nikon 60 mm lens mounted on a Nikon D300 camera. The scene was lit with a pair of Ikelite DS 160 strobes. Knowing that I wanted enough depth-of-field to have every part of the crab’s body in focus I cranked my strobes up to full power and closed my aperture down as small as I could.

I hope you enjoy this week’s POTW!

See you next week,

Marty