Discussion

Real Crabs

Crabs are decapod (ten legged) crustaceans in the infraorder Brachyura. Most live in water worldwide; fresh or salt depending on the species. Some, like the fiddler crab live on land near water, like mud flats, swamps, etc. Crabs have been around for about 200 million years.

This red rock crab (Grapsus grapsus) gives a good general idea of what crabs look like. 

Only four pairs of legs can be seen in the photo. The front pair are for feeding and defense. Food is torn to bits and fed to the mouth at the front center of the body. The remaining four pairs are for moving around. The rear two can't be seen here because they are often folded up behind the crab, leaving most of the work of walking, usually with a sideways motion, to the other three pair. Compound eyes are mounted at the top of stalks.

Crabs are encased in an armored shell that, once formed, doesn't change in size. The crab inside the shell does grow, however, requiring it to occasionally shed its shell, a process called molting. A new shell forms after a few days, leaving the crab vulnerable to predators in the meantime.

Adult crab populations tend to molt simultaneously, females in the spring, males in the late summer. It often produces a scene like this one.

Crabs may lose legs through accidents or attacks by predators. The legs often regrow after molting.

Female crabs molt before being able to mate. They release pheromones when that happens. Males attracted by the scent perform a ritual dance. When ready, females work their way under the male. This usually happens in the spring. There is a flap called an apron on the underside of females where eggs are kept. When fresh, they are a bright orange color. Blue crab females produce between 750,000 to 8 million eggs per batch. The photo below shows a Dungeness crab with her eggs exposed. 

The eggs turn blackish when they are ready to be released. Newly "hatched" crabs are called zoea. They are extremely tiny, and just about everything eats them. Out of the gigantic batch of eggs released, it is lucky if more than a couple survive to become adults. Zoea transition to another larval form called megalopae before becoming juvenal crabs.

Here is a summary of crab anatomy.

Some crabs have exaggerated features. One of the claws of the male fiddler crab, for example, is gigantic compared with the other.

Male fiddler crabs wave their large claw around to attract females. Females choose mates based on claw size and the quality of the waving display.

Another unique species is the Japanese spider crab, the largest of all crab species. It has a leg span of over 12 feet. It goes through 3 larval stages before becoming adults. They take over an hour and a half for molting; body first and then the legs.

Horseshoe Crab

One type of crab that isn't a crab is the horseshoe crab. They are much more closely related to spiders and other arachnids than to real crabs, even though they have five pairs of limbs like real crabs do instead of four. Horseshoe crabs have been around for over 300 million years. They have nine eyes scattered around their body and other light sensitive areas. The largest two are compound eyes and are useful for finding mates.

Porcelain Crab 

In spite if their very crab-like appearance, porcelain crabs are much more closely related to lobsters than to real crabs. One way to tell is their long, lobster-like antenna. Porcelain crabs are very tiny, growing to little more than half an inch in length. Their appearance can vary widely.

Hermit Crab

Though hermit crabs are closely related to real crabs, shrimp, and lobsters, they are crabs in name only. All real crabs have shells of their own. Hermit crabs do not. Instead, they must find a shell left behind by some other animal for shelter, or they die. They have a hooked tail and limbs specialized to help them cling to the inside of whatever shelter they find. Increasingly, hermit crabs are found occupying human trash.

King Crab

It may be a surprise to many, but king crabs are not real crabs, either. they are believed to be related to hermit crabs. The exact taxonomy is being hotly debated with several shifts in the past few years, the most recent of which occurred just last year. As of April this year, there are 137 recognized king crab species (including one extinct species) in 15 genera. The red king crab is the most popular food crustacean. 

Katsushika Hokusai (1760 – 1849)

Hokusai's name is well known for his ukiyo-e landscapes. His most famous series is titled Thirty-Six Views of Mt. Fuji. The first painting of that series, The Great Wave off Kanagawa (1830), is a world-famous icon. Hokusai produced many series and painted a great many subjects besides landscapes. It is not known when he painted his Crab and Rice Plant surimono, shown below. A surimono was an especially high quality, privately commissioned print, usually to mark some special occasion. Many were calendar prints. Only licensed publishers were legally allowed to print calendars during the Edo Period (1603 - 1868). Private individuals or organizations sometimes got around this by commissioning artists to produce prints that were calendars in disguise. Only those who could recognize the coding would know how to interpret them. Hokusai's Crab and Rice plant print is probably not a calendar print.

Utagawa Kunisada (1786 – 1865)

Though highly regarded in his own time, Kunisada was long thought to be an inferior ukiyo-e artist. A reevaluation that began in the 1990s has resulted in him now being regarded as one of the greats; especially for bijin-ga (pictures of beautiful people) and yakusha-e (kabuki actor prints). His Crab and Peonies print below was produced in 1825.

Ryūryūkyo Shinsai (fl. 1799 - 1823)

Ryūryūkyo studied under Hokusai. He specialized in surimono prints. This crab print was from something called Spring Rain Collection, vol. 1: Crabs and Lotus Blossoms, and was published in the 1805 –  1810-time frame.

Suzuki Nanrei (?)

No biographical information has been found for this artist except that Shibata Zeshin (1807 – 1891), an artist most known for his lacquer paintings, is supposed to have studied under him. His Crab and Flower is supposed to have been produced in the 1890 - 1900-time frame.