Crabs
by Krysta CardinaleIn general, crabs are cold-water invertebrates. There are many species of crabs that march along the sea floor. Crabs are usually found in saltwater, but a few species can be found in freshwater or even on land. With the crab species there is a discrepancy on what is actually a “true crab.” “True crabs” are argued to be mainly members of the Brachyura. These crabs five sets of legs including a set of claws, and a flattened shell. The “untrue crabs” are said to be members of the Anomura and include hermit crabs, horseshoe crabs, and porcelain crabs for example. A common misperception of crabs would be that they only walk sideways, however crabs can actually walk in any direction.
The sex of a crab can be determined on its abdomen by flipping it over. The underbelly of a male crab is narrow, whereas in a female it is much wider in order to carry eggs. Crabs mate from the months May to October. They grow from shedding their shell. Just prior to this molting, Crabs are encased in both the old hard outer shell and the new soft shell underneath it. Immediately after the old shell is shed, the crab is soft and easily stretched. Within two hours of this shed the shell begins to harden, but takes two to three days to completely harden. Little to no growth occurs for crabs in the winter months from December through March, and most will bury themselves in mud and shallow grass beds.
“True Crabs”
Species of true crabs include the Blue Crab, Fiddler Crab, Coconut Crab, Land Crab, Spider Crab, Oyster Crab, Rock Crab, Sponge Crab, Stone Crab, and the Snow Crab.
• Blue Crabs
The Blue Crab is found in the waters from Nova Scotia to Argentina and in North America from Texas to Massachusetts. Blue Crabs are omnivores and eat such things as a variety of live and dead fish, crabs, clams, snails, eelgrass, sea lettuce, and decayed vegetation. They are a preferred crab on the market for their sweet white meat. The Blue Crab’s most prominent feature would be its large and powerful claws. These claws are used for defense, food gathering, digging, and sexual displays. Blue Crabs get their name for the blue color found on its legs and claws.
• Fiddler Crabs
The Fiddler Crab is a small crab not caught for consumption ranging in size from about one to two inches. They are found in sandy or muddy beaches and mangroves of West Africa, the Western Atlantic, Eastern Pacific, and the Indo-Pacific. Fiddler Crabs are also known as “Calling Crabs.” They are known for their asymmetrical pair of claws. They have one oversized claw, and one small claw. Fiddler Crabs range in color and can be tan, blue-green, yellow, black, turquoise, or orange. They only live a lifespan of about two years.
• Coconut Crabs
The Coconut Crab is the largest land arthropod known in the world. The size of this crab is said to weigh up to nine pounds, a leg span of three feet, and a body diameter of sixteen inches. Coconut Crabs can live up to 30-60 years. These large crabs lives mostly in underground burrows or rock crevices, and remains there during the day. Adult Coconut Crabs cannot swim, however their eggs are hatched in water, and their larvae floats in the water for a period of twenty-eight days. Young Coconut Crabs live on the bottom of the ocean like hermit crabs for another twenty-eight days before they come and remain on land. Coconut Crabs eat a variety of mainly fruits, but will also eat anything organic including rotting leaves and dead animals. They get their names from their large claws that can crack the shells of coconuts. These crabs can be found in areas throughout the Indian and Western Pacific oceans. Based on the location where a Coconut Crab is found determines its coloring, ranging from light violet through deep purple to brown.
• Land Crabs
The Land Crab is yet another crab that lives mainly on land, using the ocean only to reproduce. The Land Crab is found Bermuda, the Florida Keys and along the Coast of mainland Florida, as well as from the coast of Texas to Brazil. This crab is similar in look to the Blue Crab, and is also edible. The Land Crab is a scavenger type feeder, eating similar to the Coconut Crab. It remains hidden during the day and comes out at night to feed on anything from garbage scraps, to fruit, to rotting fish.
• Spider Crabs
Among the spider crabs there are several different types. The Common Spider Crab has a spiny shell and is covered with tiny hairs. It grows to be about four inches in diameter and it ranges in color from dull yellow to brown. The Common Spider Crab is a slow moving scavenger. The tiny hairs it has are used as defensive camouflage. They attract algae, barnacles, and other debris to help it blend into the sea floor. It is found along the entire East Coast of the United States. Another type is the Japanese Spider Crab. It is the largest known crab alive weighing up to 44 pounds with a leg span of about thirteen feet, and a body diameter of about 15 inches. It can be found at the bottom of the Pacific Ocean around Japan. Similar to the Common Spider Crab, the Japanese Spider Crab is a scavenger and typically eats shellfish and dead animals. It has two distinct horns that protrude from between its eyes, and the younger crabs are covered with tiny hairs and thorns. The Japanese Spider Crab is orange in color with white spots on its legs, and the males’ claws outgrow their other legs.
• Oyster Crabs
The Oyster Crab is generally a tiny soft-bodied crab that lives within the mantle cavity of oysters. Since it has a soft shell it relies on the outer hard shell of the oyster for protection. The Oyster Crab attaches itself to the gills of an oyster and remains within the shell eating algae and other materials. Oyster Crabs are so tiny that as many as a dozen can be found inside of one oyster.
• Rock Crabs
Red Rock Crabs are found along the southern Australian shores. It is one of the fastest moving crabs. It is considered a very aggressive crab, but typically feeds off of small seaweeds. Red Rock Crabs can grow up to 18 centimeters in diameter. They are usually only active at night and cannot be seen during the day. Common Rock Crabs are another name for Common Spider Crabs, which are found along the whole Eastern Coast of the United States.
• Sponge Crabs
The Sponge Crab is another nocturnal crab. They use their rearmost pair of legs to grab a live piece of sponge, which they then carry around as part of their disguise. It is typically a slow mover and has a covering of algae that also serves as a disguise. It is so good at hiding itself that they can only be seen by a sharp eye when they move. Sponge Crabs are usually found off the shores of North Whales and the UK. Like many other crabs, it is a scavenger and feeds on pretty much anything.
• Stone Crabs
The Stone Crab is more commonly known as the King Crab. They are known as large crabs, and regularly caught and sold for food. King Crabs are found in cold waters typically off the coast of Alaska. In the King Crab family there are the Red King Crab, the Blue King Crab, the Golden King Crab, and the Scarlett King Crab. The Red, Blue, and Golden King Crabs are frequently fished, whereas the Scarlett is not due to its small size and small population. The Red King Crab is the most popular consumed and most expensive crab on the market. It is named after the red color its shell turns when it is cooked. The Blue King Crab is actually the biggest of all king crabs. It resembles and tastes like the Red King Crab. The Golden King Crab is noticeably smaller than the red and blue king crabs. Even though they taste similar, the golden ones are sold cheaper due to their size.
• Snow Crabs
The Snow Crabs are typically found in colder waters of the Pacific and Atlantic Oceans. The bodies of Snow Crabs grow to be about four inches in diameter. Like the King Crab, the Snow Crab is known for its delicious meaty white leg meat, making it a commercially fished crab. It generally has a lifespan up to thirteen years old. Snow Crabs are also referred to as “Queen Crabs,” and is considered the most important crab harvested in the Atlantic Ocean.
“Untrue Crabs”
The “untrue crabs” are considered part of the crab family because of their hard shells and somewhat crab like appearance. However these crabs are actually members of the Anomura and not the Brachyura classification like “true crabs.” Members of “untrue crabs include Hermit Crabs, Horseshoe Crabs, and Porcelain Crabs.
• Hermit Crabs
Hermit Crabs are decapod crustaceans. Hermit Crabs are known for their shell casings which they scrounge up as a defense for their soft bodies. As a hermit crab grows it loses the shell it was “wearing,” and finds and inhabits a larger one. There are approximately 500 known species of hermit crabs. They are usually sea dwelling, but some species are terrestrial. Several common species of hermit crab are used in aquariums because they are scavengers that keep the tank clean, eating algae and other debris. The lifespan of hermit crabs ranges from normally 2-5 years to 20-30 years. Common smaller hermit crabs include the Scarlet Hermit Crab and the Zebra Hermit Crab. The most popular land dwelling hermit crabs are the Caribbean Hermit Crab and the Pacific Hermit Crab. In Europe, the most familiar hermit crab is the Common Hermit Crab.
• Horseshoe Crabs
Horseshoe Crabs are chelicerate arthropods making them more related to scorpions and spiders than crabs. Horseshoe Crabs are usually found in the Gulf of Mexico and along the North-Eastern coast of North America. They survive by eating annelid worms, mollusks, and other invertebrates. Horseshoe crabs have a pair of pincers on either side of their mouths that they use to capture their food. On this diet they can grow up to twenty inches in size. Horseshoe crabs use a five gills located at their appendages to breathe underwater and also on land for a short amount of time. A unique feature of this species would be that it has four eyes. The body of a horseshoe crab can be divided into three parts based on its shell. There is the smooth, rounded front shell of the crab called the “carapace.” The middle portion is the “abdomen,” and the last part is the “telson.” The “telson” is the hard tail-like piece of the Horseshoe Crab that it uses to flip itself if turned over. The Horseshoe crab can live from about 16-20 years.
• Porcelain Crabs
Porcelain Crabs, like Hermit Crabs, are decapod crustaceans. They resemble “true crabs,” and are located in all oceans except the Antarctic and Atlantic. They are very small in size with bodies only reaching 1-2 centimeters in width. Porcelain Crabs can be distinguished from real crabs because they have only three sets of walking legs compared to the “real” four. Porcelain Crabs have a body similar to the squat lobster, however it is more flattened and compact. This is due to the fact that they are usually found under rocks on rocky coasts. Porcelain Crabs have delicate limbs that they can break off if caught by a predator or stuck under a rock, and this limb will regenerate over a period of time. The claws on the Porcelain Crab are not used for eating, but for territorial gain. They usually stick to eating plankton and other soft organic plants, but can also consume the softer meaty parts of dead fish or shrimp.
