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14 Facts About Xanthidae (Xanthid Crab)

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Xanthidae, also known as xanthid crabs or mud crabs, are a diverse family of small to medium-sized crabs that live in tropical and subtropical coastal marine waters around the world. Here are 14 interesting facts about these colorful crustaceans:

Facts About Facts

Xanthidae>Atergatis floridus Floral egg crab IMG8548
Xanthidae>Atergatis floridus Floral egg crab IMG8548
  • Xanthid crabs have a square-shaped carapace. Their carapace (top shell) is typically wider than long, giving them a box-like appearance from above.
  • There are over 500 species. The Xanthidae family contains a huge variety of crab species with different shapes, sizes, and colors. Some of the most common genera include Panopeus, Eurypanopeus, and Menippe.
  • They are found worldwide. Xanthid crabs can be found along coastlines of every continent except Antarctica. They thrive in shallow, warm waters of harbors and estuaries.
  • Most eat algae and debris. The majority of xanthid crabs are omnivores or scavengers. Using their claws like tweezers, they pick food particles off rocks and sediment.
  • Some species eat mollusks. Crabs like the stone crab (Menippe species) use their strong claws to prey on oysters, clams, and mussels. Their claws can easily crack through shells.
  • Xanthids walk sideways. Like all crabs, they have legs specialized for sideways movement instead of forward. This helps them hide in narrow spaces and crevices.
  • They have small eggs. Female xanthid crabs carry 100,000 to 500,000 tiny eggs at a time. After hatching, the larvae float as zooplankton before settling on the seafloor.
  • Many decorate their shells. Smaller xanthid crabs often adorn themselves with sponges, algae, hydroids, or anemones that help camouflage them against predators.
  • Some species are eaten by humans. The tasty blue crab (Callinectes sapidus) is the most economically important xanthid, supporting fisheries across North America.
  • Xanthids molt their exoskeleton. As they grow, xanthids shed their rigid outer shell. After molting, they pump themselves up by swallowing water to expand their new soft shell.
  • They have stalked eyes. Their eyes sit on the ends of eyestalks that can bend and swivel, giving xanthids nearly 360° vision to watch for danger.
  • Males have one large claw. Male xanthids usually have one enlarged crusher claw used to grasp and defend females during mating. Females have smaller, more evenly sized claws.
  • Some species are invasive. A few xanthid mud crabs, like the European green crab, have been introduced around the world and become aggressively invasive. They outcompete native crabs and shellfish.

Frequently Asked Questions

Where can I find more information about Hawaiian xanthid crabs?

You can find more information about Hawaiian xanthid crabs on various websites such as the Marshall Islands website by Scott and Jeanette Johnson, Dr. Peter Castro’s checklist of all crabs known from the Hawaiian Islands, and Charles H. Edmondson’s “Xanthidae of Hawaii” (1962).

Are there any unidentified xanthid crabs in Hawaii?

Yes, there are some unidentified xanthid crabs in Hawaii. Photos of these crabs can be found on websites like Keoki Stender’s Marine Life Photography website. Specialists like Dr. Peter Ng at Singapore National University can help with identification.

What is known about the Hawaiian crab species Liomera tristis?

iomera tristis is a small xanthid crab found in Hawaii. It has been observed in coral depressions and is known to remain still even when approached. The last formal record of this species in Hawaii was in 1906.

What is the distribution of Leptodius sanguineus?

Leptodius sanguineus is one of the most common shoreline crabs in Hawaii. It can often be seen crawling in shallow tidepools, feeding on algae. It is known to be distributed from East Africa and the Red Sea to the Eastern Pacific.

With colorful bodies, sideways scuttling, and their ability to decorate themselves with “living jewelry,” xanthid crabs are one of the most fascinating and diverse crab families along tropical shorelines around the globe. Learning more about their identification, ecology, and behavior reveals what makes them such successful crustaceans.

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