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The Explorer's Guide contains a treasure trove of aquatic science resources developed for use in K-12 classrooms. Back to Explorer's Guide.

Anemone Porcelain Crab Scientific Name: Petrolisthes maculates
If attacked by a predator that grabs hold of a claw or leg, the porcelain crab can cast off the limb then slip away before the attacker realizes the rest of it is gone. But why would it want to lose such a valuable part of its body? This strategy helps to keep the crab from getting an infection in an open wound where the predator would have bit it. Releasing the limb from where it connects to the body, the crab then seals off the area. Eventually, the porcelain crab will regrow or regenerate the leg or claw.

Region: Philippines

Like a delicate piece of china, the porcelain crab looks very fragile. It is actually protected quite well. The crab has a rigid outer covering called an exoskeleton. While the crab grows, it periodically molts or sheds its exoskeleton and produces a new larger one. Just before molting, the crab produces a new soft exoskeleton under its outer one. When the crab starts to burst out of its shell, the old exoskeleton splits where the body and the tail come together. The crab crawls out of the old exoskeleton and leaves it on the reef. In order to fit into the new larger exoskeleton, the crab pumps its body cells full of water. During the period after it molts, the crab must be extra careful and take shelter inside a deep reef crevice. The new exoskeleton is soft, making it easy for predators to eat it. Once the new exoskeleton is hard, the body cells pump out the extra water and the body is ready to grow into its new shell.

The anemone porcelain crab has a tail, but it keeps it tucked under its body. It also has 10 legs, like other crustaceans or animals without backbones that have a protective hard outer shell. The last pair of legs is so small in the porcelain crab that it looks like they only have 8 legs. This tiny crab is only about one inch (2.5 cm) wide.

They are found all over the reef under rocks and even under large rocks near the shore. Porcelain crabs can be found from the surface to depths of 67 feet (20 m). They can also be found snuggly living inside the dangerous tentacles of the giant anemone. If approached by predators, the porcelain crab can dive inside the safety of the tentacles or it may even hide inside the mouth of the anemone. Some porcelain crabs live among masses of feather stars, mussels, sponges, corals, or algae.

Porcelain crabs live in the warm parts of the Pacific Ocean.

Sweeping the water for zooplankton or tiny animals and phytoplankton or tiny plants, porcelain crabs use their feathery arms like fishing nets to capture their food.

A male deposits a spermatophore or packet of sperm onto the female’s chest area where all the legs attach. This is often called the ‘tar spot’ because the spermatophore is a dark black color. After the female produces her eggs, she will break open the spermatophore to release the sperm, which fertilizes her eggs. Female porcelain cleaner crabs can produce up to 1,600 eggs each time. The eggs remain under the female for about four weeks and eventually turn brown. When they hatch, the females fans her tail, releasing her young into the open ocean as planktonic larvae or larvae that live in the upper layer of the ocean and float there until they reach a certain size. This spreads out the larvae over a wide range of areas.

>A species or group of organisms that is in danger of extinction or disappearing from the face of the earth in the near future if its situation is not improved.

A species that can be found throughout its natural range but is declining in number and may become endangered in the absence of special protection efforts.

A species that is not declining in number but is of special concern because it is sensitive to pressure by particular human activities or natural events.

A species that is not declining in number and is not sensitive to pressures by human activities or natural events.

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Threats and Management
Porcelain crabs are often found near the shore living under large rocks where people can easily search for them. These crabs are so small that they are not of much value as food, but if they are taken and put into a home aquarium, they don’t often survive. Since these animals can live in a wide variety of habitats like the reef, their population remains stable.

Did You Know?
Not even the hard shell serves to protect this crustacean. There is a barnacle that will attach and cement itself to a porcelain crab. Next the barnacle drills a hole in the crab’s shell and takes over its body. It will attack the crab from the inside out by feeding off the crabs body fluids and tissue. The barnacle prevents the crab from molting, so the crab can’t shed its shell to get rid of the barnacle. When the barnacle is ready to reproduce, it places its own eggs on the crab’s belly. The crab cares for the eggs as if they were its own. The barnacle will stay with the crab for an entire reproductive season, producing over a million new barnacles. Eventually, the crab will die and the barnacle will seek out another crab as its host.

Like a house fly, the porcelain crab has compound eyes. The eye is made of thousands of tiny cylinders that each have their own lens and light receptor. Each cylinder can see part of the image before them, creating a mosaic out of what the animal is seeing. The eyes of the tiny crab are high on stalks and protected by a clear casing that is part of the crab’s hard outer shell. Having eyes up high gives the crab a complete view in front and to the sides.

Print Publications:
Allen, G. R. & Stene, R. 1996. Indo-Pacific Coral Reef Field Guide. El Cajon, California: Odyssey Publishing Company. 378p. ISBN# 981-00-5687-7.

Allen, G. R. 1997. Tropical Marine Life. North Claredon, Vermont: Periplus Editions Ltd. 64p. ISBN# 962-593-157-0.

Banister, K. & Campbell, A. 1988. Encylopedia of Aquatic Life. New York, New York: Equinox (Oxford) Ltd. 349p. ISBN# 0-8160-1257-101-X.

Colin, P. L. & Arneson, C. 1995. Tropical Pacific Invertebrates. Beverly Hills, California: Coral Reef Press. 296p. ISBN# 0-9645625-0-2.

Coleman, N. 1999. Dangerous Sea Creatures Aquatic Survival Guide. Australia: Neville Coleman’s Underwater Geographic Pty Ltd. 95p. ISBN# 0-947325-24-7.

Coulombe, D. A. 1984. The Seaside Naturalist. A Guide to Study at the Seashore. New York, New York: Prentice Hall Press. 246p. ISBN# 0-13-79710.

Grosliner, T.M., Behrens, D.W., & Williams, G.C. 1996. Reef Animals of the Indo-Pacific. Monterey, California: Sea Challengers. 314p. ISBN# 0-930118-21-9.

Hoover, J. P. 1998. Hawai’i’s Sea Creatures. A Guide to Hawa’i’s Marine Invertebrates. Honolulu, Hawaii: Mutual Publishing. 366p. ISBN# 1-56647-220-2.

Perrine, D. 1997. Mysteries of the Sea. Lincolnwood, Illinois: Publications International, Ltd. 312p. ISBN# 0-7853-2430-5.

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Vocabulary Words

Berried – When a female crab sticks her bright red eggs to her abdomen.

Crustacean – An animal without a backbone that has a protective hard outer shell.

Exoskeleton – A hard external skeleton that encases, protects and supports the soft body of animals like crustaceans.

Extinction – An organism that has not been present on the face of the earth for over 50 years.

Invertebrate – An animal without a backbone.

Molt – The periodic process of shedding an exoskeleton as crustaceans grow.

Organism – A living thing.

By-catch – The part of the fisher's catch which is returned to the sea either because it has no value to them. Fishing boats search the seas for target animals, like tuna, and discard anything else they accidentally catch—like sharks. The unwanted animals, called by-catch, dry out or suffocate on the deck, or get thrown back into the ocean all but dead.

Overfishing – The excessive fishing or catching of aquatic (ocean or freshwater) animals to the point that the amount of animals being caught is greater than the amount of animals born. When more animals are caught than are being born, the aquatic environment is left depleted of the targeted animals.

Planktonic larvae – Newly born animals that live in the upper layer of the ocean and float there until they reach a certain size. This spreads out the larvae over a wide range of areas.

Species – A group of organisms capable of breeding and producing fertile offspring; organisms that share the same gene pool.

Spermatophore – A packet of sperm that is deposited onto a female’s body. The spermatophore will be used when the female has fully developed eggs that are ready to be fertilized.

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Anemone Porcelain Crab
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