crustacean

[krəˈstāSH(ə)n]

NOUN

crustaceans (plural noun)

1. an arthropod of the large, mainly aquatic group Crustacea, such as a crab, lobster, shrimp, or barnacle.

What are the different types of crustaceans?

crustacean are various predominantly aquatic arthropods of the class Crustacea, including lobsters, crabs, shrimps, and barnacles, characteristically having a segmented body, …a chitinous exoskeleton, and paired, jointed limbs Amollusks is a numerous chiefly kinds of marine invertebrates of the phylum Mollusca

Barnacles are arthropods of the subclass Cirripedia in the subphylum Crustacea. They are related to crabs and lobsters, with similar nauplius larvae. Barnacles are exclusively marine invertebrates; many species live in shallow and tidal waters. Some 2,100 species have been described.

Barnacle adults are sessile; most are suspension feeders with hard calcareous shells, but the Rhizocephala are specialized parasites of other crustaceans, with reduced bodies. Barnacles have existed since at least the mid-Carboniferous, some 325 million years ago.

In folklore, barnacle geese were once held to emerge fully formed from goose barnacles. Both goose barnacles and the Chilean giant barnacle are fished and eaten. Barnacles are economically significant as biofouling on ships, where they cause hydrodynamic drag, reducing efficiency.

Most barnacles are encrusters, attaching themselves to a hard substrate such as a rock, the shell of a mollusc, or a ship; or to an animal such as a whale (whale barnacles). The most common form, acorn barnacles, are sessile, growing their shells directly onto the substrate, whereas goose barnacles attach themselves by means of a stalk.

Barnacles have a carapace made of six hard calcareous plates, with a lid or operculum made of four more plates. Inside the carapace, the animal lies on its stomach, projecting its limbs downwards. Segmentation is usually indistinct; the body is more or less evenly divided between the head and thorax, with little or no abdomen. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae attached to the cement gland. The eight pairs of thoracic limbs are called cirri; these are feathery and very long. The cirri extend to filter food, such as plankton, from the water and move it towards the mouth.

Barnacles pass through two distinct larval stages, the nauplius and the cyprid, before developing into a mature adult. 

Most barnacles are filter feeders. From within their shell, they repeatedly reach into the water column with their cirri. These feathery appendages beat rhythmically to draw plankton and detritus into the shell for consumption.

Although they have been found at water depths to 600 m (2,000 ft), most barnacles inhabit shallow waters, with 75% of species living in water depths less than 100 m (300 ft), and 25% inhabiting the intertidal zone. Within the intertidal zone, different species of barnacles live in very tightly constrained locations, allowing the exact height of an assemblage above or below sea level to be precisely determined.

Since the intertidal zone periodically desiccates, barnacles are well adapted against water loss. Their calcite shells are impermeable, and they can close their apertures with movable plates when not feeding. Their hard shells are assumed by zoologists to have evolved as an anti-predator adaptation.

One group of stalked barnacles has adapted to a rafting lifestyle, drifting around close to the water's surface. They colonize every floating object, such as driftwood, and like some non-stalked barnacles attach themselves to marine animals. The species most specialized for this lifestyle is Dosima fascicularis, which secretes a gas-filled cement that makes it float at the surface.

Among the most common predators of barnacles are whelks. They are able to grind through the calcareous exoskeleton and eat the animal inside. Barnacle larvae are consumed by filter-feeding benthic predators including the mussel Mytilus edulis and the ascidian Styela gibbsi. Another predator is the starfish species Pisaster ochraceus. A stalked barnacle in the Iblomorpha, Chaetolepas calcitergum, lacks a heavily mineralised shell, but contains a high concentration of toxic bromine; this may serve to deter predators. The turbellarian flatworm Stylochus, a serious predator of oyster spat, has been found in barnacles. Parasites of barnacles include many species of Gregarinasina (alveolate protozoa), a few fungi, a few species of trematodes, and a parasitic castrator isopod, Hemioniscus balani. 

Of the more than 1,400 species of barnacles found in the world’s waterways, the most common ones are called acorn barnacles. As anyone who’s ever maintained a vessel knows, removing barnacles requires some elbow grease (or a pressure washer). That's why some boaters call them by their slang name: "crusty foulers."

How do barnacles stick to the undersides of vessels, to other sea life, to each other, and to pretty much anything they come in contact with? They secrete a fast-curing cement that is among the most powerful natural glues known — the glue is so strong that researchers are trying to figure out how it can be used commercially.

Barnacles like places with lots of activity, like underwater volcanos and intertidal zones, where they reside on sturdy objects like rocks, pilings, and buoys. Moving objects like boat and ship hulls and whales are particularly vulnerable to the pesky critters. Large barnacle colonies cause ships to drag and burn more fuel, leading to significant economic and environmental costs. The U.S. Navy estimates that heavy barnacle growth on ships increases weight and drag by as much as 60 percent, resulting in as much as a 40 percent increase in fuel consumption!

Barnacles feed through feather-like appendages called cirri. As the cirri rapidly extend and retract through the opening at the top of the barnacle, they comb the water for microscopic organisms. They quickly withdraw into their protective shells if they sense a potential threat. Barnacles secrete hard calcium plates that completely encase them. A white cone made up of six calcium plates forms a circle around the crustacean. Four more plates form a "door" that the barnacle can open or close, depending on the tide. When the tide goes out, the barnacle closes up shop to conserve moisture. As the tide comes in, a muscle opens the door so the feathery cirri can sift for food.

Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tail" in Greek), which typically have a very short projecting tail-like abdomen, usually hidden entirely under the thorax. They live in all the world's oceans, in freshwater, and on land, are generally covered with a thick exoskeleton, and have a single pair of pincers on each arm. They first appeared during the Jurassic period, around 200 million years ago. 

Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized chitin. Behind their pair of chelae (claws) are six walking legs and then two swimming legs. The crab breathes through gills on its underside; gills must be at least moist to work.

Crabs vary in size from the pea crab, a few millimeters wide, to the Japanese spider crab, with a leg span up to 4 m (13 ft). Several other groups of crustaceans with similar appearances – such as king crabs and porcelain crabs – are not true crabs, but have evolved features similar to true crabs through a process known as carcinisation

Crabs often show marked sexual dimorphism. Males often have larger claws, a tendency that is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae). In fiddler crabs, males have one greatly enlarged claw used for communication, particularly for attracting a mate. Another conspicuous difference is the form of the pleon (abdomen); in most male crabs, this is narrow and triangular in form, while females have a broader, rounded abdomen. This is because female crabs brood fertilised eggs on their pleopods. 

Crabs attract a mate through chemical (pheromones), visual, acoustic, or vibratory means. Pheromones are used by most fully aquatic crabs, while terrestrial and semiterrestrial crabs often use visual signals, such as fiddler crab males waving their large claws to attract females. 

Crabs typically walk sideways (hence the term crabwise), because of the articulation of the legs which makes a sidelong gait more efficient. Some crabs walk forward or backward, including raninids, Libinia emarginata and Mictyris platycheles. Some crabs, like the Portunidae and Matutidae, are also capable of swimming, the Portunidae especially so as their last pair of walking legs are flattened into swimming paddles.

Crabs are mostly active animals with complex behaviour patterns such as communicating by drumming or waving their pincers. Crabs tend to be aggressive toward one another, and males often fight to gain access to females. On rocky seashores, where nearly all caves and crevices are occupied, crabs may also fight over hiding holes. Fiddler crabs (genus Uca) dig burrows in sand or mud, which they use for resting, hiding, and mating, and to defend against intruders.

Crabs are omnivores, feeding primarily on algae, and taking any other food, including molluscs, worms, other crustaceans, fungi, bacteria, and detritus, depending on their availability and the crab species. For many crabs, a mixed diet of plant and animal matter results in the fastest growth and greatest fitness. Some species are more specialised in their diets, based in plankton, clams or fish.

Crabs are known to work together to provide food and protection for their family, and during mating season to find a comfortable spot for the female to release her eggs.

5 Things You Didn't Know About Blue Crab

By KIMBERLY HOLLAND

Blue crabs are one of the most recognizable varieties of shellfish. They’re small—mature males are only about nine inches wide—and their lifespan is rather short, just 3 years on average. Blues are also one of the most popular sources of food for many coastal communities. Here, learn a bit more about these colorful crustaceans.  

Their Scientific Name Suggests They’re Delicious

The blue crab’s scientific name is Callinectes sapidus, which translates to “savory beautiful swimmer.”

Indeed, their back legs, which are paddle shaped, make them excellent swimmers. And blue crabs are prized for their sweet, delicate flavor and tender meat. Blues are among the most heavily harvested creatures across the world, and typically fetch high prices in ports around the world.

Males and Females Look Different

While both sexes have sapphire-tinted claws, females have an additional display of color: red highlights on the tips of their pincers.

Likewise, flip a blue crab over, and you can spot the sex by taking a look at the crab’s “apron.” The apron is the folded surface of the belly, which comes in three distinct shapes: T-shaped on male abdomens, triangular on young females, and rounded and circular on older females.

Their Natural Habitat Is Large—and Expanding

These delightfully colorful crabs take up residence in waters from Nova Scotia to the Gulf of Mexico, and even further south along the coasts of Argentina and Uruguay. Nowhere is the crab more iconic, though, than the Chesapeake Bay. In the waters off Maryland and Virginia, the blue crab population thrives in the brackish estuaries and salt marshes.

Stowaway blue crabs on ship ballasts have even showed up in the Mediterranean. There, however, the crab is invasive. It was first seen off Egyptian waters in the 1940s, but reports of blue crab sightings in Italy, Israel, Greece, and Turkey have been made, too. As such, many coastal communities have found ways to use the foreign crustaceans as a source of food and income.

Females Mate Just Once

Blue crab mating season stretches from May to October. Once females reach sexual maturity, they mate with a male only once. (Males will mate with multiple females during their lifespan.)

Once the crabs mate, an egg mass develops beneath the female’s apron. This mass, or sponge, can contain as many as 2 million eggs. In about two weeks, the eggs are released into the waters, and they’re carried in currents out into the ocean. There, the blue crab larvae, or zoea, molt over 25 times and grow before the maturing crabs make their way back to the estuaries and salt marshes to start their own reproductive process.

Blue Crabs Will Eat Almost Anything

When it comes to their diet, blue crabs aren’t particularly picky. They eat clams, mussels, snails, dead fish, plants, and more. If they can’t find other food sources, blue crabs will even eat smaller, less mature blue crabs.

Blue crabs actually help manage the populations of the animals and fish they eat, so during periods of overfishing—as has happened in recent decades, especially in the Chesapeake Bay—the loss of blue crabs has negative effects on the ecosystem where the crabs once hunted and ate.

Catching blue crabs isn’t complicated, but there are a few fundamentals you need to know in order to be successful. First of all, these critters are nocturnal. While you may see an occasional straggler hanging around during the day, they seem to appear from behind every rock in the bay as soon as the sun goes down. They tend to favor shallow bays, harbors and estuaries with soft muddy bottoms. The best times to target them are August and September.

You should know that blue crabs are lightning fast, and yes, they do indeed swim – they don’t just awkwardly stumble their way across the bottom like most of their relatives. When they do swim, they either go directly right or left. Blue crabs are equipped with two paddle-like legs, one on each side of their body. And they are comfortable at a wide range of depths.

Blue crabs are one of the most ferocious life forms in the sea. They have attitude. Their claws are powerful and speedy, even out of the water. When you do manage to capture one, there is only one way to safely grab hold of them, which is by pinching the back part of the top and bottom of the body. Just don’t put your fingers too far forward, as they can extend those big blue claws underneath their bodies for quite a ways.

There are a few different techniques for catching blue crabs, none of which is very complicated or hard to master. A favorite is called the “hunt and peck” method. All you really need is a long-handled net, a powerful flashlight and a 5-gallon bucket. A pair of waders is nice, but not essential. You can venture out in an old pair of sneakers, but if you stumble into a deep mud hole, it may consume one of your sneakers. Try wearing waders instead. Another reason is when you look around in an estuary at night, you’re bound to see some creatures that would give even the most seasoned sea captain the willies. These places come to life at night. You will come across countless large-size eels, alien-looking spider crabs, bizarre worms, jellyfish and toadfish. The neoprene waders become your armor.

As far as nets go, you want a “fast” net. One that has a small diameter opening, no more than 15 inches or so. The netting should be relatively shallow, since blue crabs have the tendency to hang onto the mesh for dear life once they’ve been scooped up. It should also have a wide mesh that doesn’t create a lot of water resistance. The faster you can move it around underwater, the better it will be. The handle should be at least five to six feet long.

When the sun goes down, it’s time to head to an estuary. Some prefer going out close to the low tide, but this is not essential. It helps to have a running tide, since the moving water will clear up the water faster. Blue-crabbing is always best when you are accompanied by a buddy. Both people should be equipped with a net and a spotlight or powerful flashlight, and one of you will have to be the bucket-carrier. You will have to cover a lot of ground to be successful, since your feet are going to stir up the bottom, reducing visibility.

Start out in about three feet of water and move parallel to the shoreline. It shouldn’t take long to catch sight of your first victim. Once you’ve spotted a blue crab, keep your light on it and send your buddy out around 10 feet from it, into deeper water. Have him corral the crab back toward you. Usually your spotlight will have the “deer in the headlights” effect, and the crab will freeze with its claws raised, ready for battle. Other times the crab will get squirrelly and bolt for deeper water. Keep in mind that the crab will go either left or right, so if you set up on it correctly, it will bolt toward one of your nets, which should already be underwater near the bottom. If you’re quick enough, you will bag it on your first attempt. If you miss – and you will have plenty of misses – try to chase the critter into shallow water where it’s easier to spot again. Once you’ve made a successful capture, flip your net upside down over the 5-gallon bucket and shake it until the crab lets go of the netting. Never try to force the crab out of the net, since that will often separate one of the delicious claws from the crab’s body.

Once you have managed to catch a few blue crabs, you will be faced with a new dilemma. Blue crabs have the tendency to fight each other until death when confined in a small area. This usually results in the largest crab ripping the claws off of all the others. One thing I’ve learned to minimize this kind of damage is to place large clumps of seaweed in with your catch. The crabs will tend to box up and hide, rather than tear each other apart.

Another technique that will aid in your “hunt and peck” approach is to set out bait as you work the shoreline. Take along some fish racks or old bait and periodically drop them in as you are walking. At some point you are going to have to turn around and work back in the direction you came from. If you have strategically placed some baits, oftentimes they will attract a crowd of blue crabs for your return trip. Once a blue crab has found a meal, it will hang tight and defend it with its life. Usually the biggest crab in the neighborhood will claim the prize, and when they are sitting on food they become a lot easier to catch.

There is another crabbing technique that works equally well and requires less work. If you happen to have a boat that is docked or moored in a clean body of water, you might want to consider picking up a crab pot. A crab pot works similarly to a lobster pot. The pots are baited and sent to the bottom, attached by rope to a float. Bait them up before you head out for a day of fishing, and check them upon returning. You can capture blue crabs during the day using this method, since they are willing to venture out of hiding for a free meal. You don’t want to leave your crab traps in the water for more than 6 to 8 hours, since once the bait is gone the crabs will turn on each other, often resulting in one large survivor-crab.

Another tactic is the “chicken wing” style of crabbing. This can be a lot of fun, and kids seem to really get a kick out of it. This is perhaps the simplest technique. Here’s how you do it. Pick up a small pack of chicken wings at the market. Find some sticks and wedge them into the sand along the shoreline about every 20 feet or so. (This technique also works great on piers, bridges and docks.) Using a 10- to 20-foot piece of twine or string, tie one end to the chicken wing and the other to the stick in the sand. Set up a bunch of these “rigs,” throw the wings out into the water, pull in the slack, sit, and wait. When a crab grabs one of the chicken wings, you’ll see the string start to dance. Grab the string and very, very slowly and steadily pull it toward shore. The crab will hold onto that chicken wing for dear life, not wanting to give up a free meal to one of its competitors. Pull it right up to the dock or shore, and then bag it with a net.

Once you capture some delicious blue crabs, it’s time for a feast. They are delicious and should be eaten soon after they are caught. They won’t last very long in a refrigerator; boil them all up the same night they’re caught. The preferred method of cooking them is quite simple. Steam them up (similar to lobsters) for about 8 to 10 minutes, and they’re ready to eat or be stored in the fridge. You can separate all of the claws off the steamed crabs and save those to eat with melted butter. Simply steam the claws for about 3 minutes to reheat them. You can take all of the bodies and pick the meat out over the sink. This can be used for crabcakes, a bisque, or whatever other recipe you desire.

The meat is very similar to lobster but it’s a lot sweeter. Most of the meat is inside the body, at the base of the legs. Split the bottom section of the crab away from the top shell, and crack it in half. Some of the meat is in a small lump behind the swimmer legs, but you’ll want to have some small utensils handy to assist in getting the rest out (a chopstick works well).

Note: In Rhode Island, harvesting blue crabs at night is prohibited. Here are the local regulations in Connecticut for blue crabs:

Blue Crab No License Required

 Minimum shell width (spike tip to spike tip)

  5 inches - Hard shell

  3 1/2 inches - Soft shell

 Daily creel limit:  None

 Open Season:  May 1 - November 30

 Prohibition on egg-bearing females