crab

crab¹

—crablike, adj.

/krab/, n., v., crabbed, crabbing.

n.

1. any decapod crustacean of the suborder Brachyura, having the eyes on short stalks and a short, broad, more or less flattened body, the abdomen being small and folded under the thorax.

2. any of various other crustaceans, as the hermit crab, or other animals, as the horseshoe crab, resembling the true crabs.

3. (cap.) Astron., Astrol. the zodiacal constellation or sign Cancer.

4. (cap.) Astron. the Crab Nebula.

5. any of various mechanical contrivances for hoisting or pulling.

6. Aeron. the maneuver of crabbing.

7. Informal. the crab louse. See under louse (def. 1).

8. crabs,

a. (used with a sing. v.) a losing throw, as two aces, in the game of hazard.

b. pediculosis.

9. catch a crab, to make a faulty stroke in rowing, so that the oar strikes the water forcibly on the backstroke.

v.i.

10. to catch or attempt to catch crabs.

11. to move sideways, diagonally, or obliquely, esp. with short, abrupt bursts of speed; scuttle.

12. Aeron. (of an aircraft) to head partly into the wind to compensate for drift.

13. Naut. to drift or advance with some movement sideways, esp. when under tow.

v.t.

14. to move (a vehicle or object) sideways, diagonally, or obliquely, esp. with short, abrupt movements.

15. Aeron. to head (an aircraft) partly into the wind to compensate for drift.

[bef. 1000; ME crabbe, OE crabba; c. D krab, ON krabbi; akin to G Krebs]

crab²

/krab/, n.

a crab apple fruit or tree.

[1300-50; ME crabbe; perh. special use of CRAB¹]

crab³

—crabber, n.

/krab/, n., v., crabbed, crabbing.

n.

1. Informal. an ill-tempered or grouchy person.

v.i.

2. Informal. to find fault; complain.

3. (of hawks) to claw each other.

v.t.

4. Informal. to find fault with.

5. to make ill-tempered or grouchy; embitter.

6. (of a hawk) to claw (another hawk).

7. Slang. to spoil.

[1350-1400; ME; back formation from CRABBED]

* * *

I

Any of 4,500 species of short-tailed decapod, found in all oceans, in freshwater, and on land.

Its carapace (upper body shield) is usually broad, and its first pair of legs is modified into pincers. Most crabs live in the sea and breathe through gills, which in land crabs are modified to serve as lungs. They walk or crawl, generally with a sideways gait; some are good swimmers. Crabs are omnivorous scavengers, but many are predatory and some are herbivorous. Two of the largest known crustaceans are the giant crab of Japan (13 ft, or 4 m, from claw tip to claw tip), a spider crab; and the Tasmanian crab (up to 18 in., or 46 cm, long, and weighing more than 20 lbs, or 9 kg). Other species are less than an inch long. Well-known crabs include the hermit crab, edible crab (Britain and Europe), blue crab, Dungeness crab, fiddler crab, and king crab.

Common swimming crab (Portunus holsatus), showing its paddle-shaped feet

Dr. Eckart Pott/Bruce Coleman Ltd.

II

(as used in expressions)

blue crab

Crab Nebula

Dungeness crab

fiddler crab

hermit crab

horseshoe crab

king crab

Japanese crab

Alaskan king crab

spider crab

* * *

▪ crustacean

Introduction

 any short-tailed member of the crustacean order Decapoda (phylum Arthropoda)—especially the brachyurans (infraorder Brachyura), or true crabs, but also other forms such as the anomurans (suborder Anomura), which include the hermit crabs. Decapods occur in all oceans, in fresh water, and on land; about 10,000 species have been described.

      Unlike those of other decapods (e.g., shrimp, lobster, crayfish), crabs' tails are curled under the thorax, or midsection. The carapace (upper body shield) is usually broad. The first pair of legs is modified into chelae, or pincers.

Distribution and variety.

      Most crabs live in the sea; even the land crabs, which are abundant in tropical countries, usually visit the sea occasionally and pass through their early stages in it. The river crab of southern Europe (the Lenten crab, Potamon fluviatile) is an example of the freshwater crabs abundant in most of the warmer regions of the world. As a rule, crabs breathe by gills, which are lodged in a pair of cavities beneath the sides of the carapace, but in the true land crabs the cavities become enlarged and modified so as to act as lungs for breathing air.

      Walking or crawling is the usual mode of locomotion, and the familiar sidelong gait in the common shore crab is characteristic of most members of the group. The crabs of the family Portunidae, as well as some others, swim with great dexterity by means of their flattened paddle-shaped legs.

 Like many other crustaceans, crabs are often omnivorous and act as scavengers, but many are predatory and some are vegetarian.

      Though no crab is truly parasitic, some live commensally with other animals. One example is the little pea crab (Pinnotheridae), which lives within the shells of mussels and a variety of other mollusks, worm-tubes, and echinoderms and shares its hosts' food; another example is the coral-gall crab (Hapalocarcinidae), which irritates the growing tips of certain corals so that they grow to enclose the female in a stony prison. Many of the sluggish spider crabs (spider crab) (Majidae) cover their shells with growing seaweeds, zoophytes, and sponges, which afford them a very effective disguise.

      The giant crab of Japan (Macrocheira kaempferi) and the Tasmanian crab (Pseudocarcinus gigas) are two of the largest known crustaceans. The former may span nearly 4 m (12 feet) from tip to tip of its outstretched legs. The Tasmanian crab, which may weigh well over 9 kg (20 pounds), has much shorter, stouter claws; the major one may be 43 cm 17 inches) long; the body, or carapace, of a very large specimen may measure 46 cm (18 inches) across. At the other extreme are tiny crabs measuring in adulthood scarcely more than a centimetre or two in length.

      Better-known anomuran crabs are the hermit crabs (hermit crab), which live in empty shells discarded by gastropod mollusks. As the crab grows, it must find a larger shell to occupy. If the supply of empty shells of appropriate size is limited, competition for shells among hermit crabs can be severe. In tropical countries hermit crabs of the family Coenobitidae live on land, often at considerable distances from the sea, to which they must return to release their larvae. The large robber, or coconut, crab (another anomuran) of the Indo-Pacific islands (Birgus latro (robber crab)) has given up the habit of carrying a portable dwelling, and the upper surface of its abdomen has become covered by shelly plates.

      As in most crustaceans, the young of nearly all crabs, when newly hatched from eggs, are very different from the parents. The larval stage, known as the zoea, is a minute transparent organism with a legless, rounded body, that swims and feeds in the plankton. After casting off its skin several times, the enlarging crab passes into a stage known as the megalopa, in which the body and limbs are more crablike, but the abdomen is large and not folded up under the thorax. After a further molt the animal assumes a form very similar to that of the adult. There are a few crabs, especially those living in fresh water, that do not pass through a series of free-living larval stages but instead leave the eggshell as miniature adults.

Economic importance.

  Many crabs are eaten by humans. The most important and valuable are the edible crab of the British and European coasts (Cancer pagurus; see photograph—>) and, in North America, the blue crab (Callinectes sapidus) of the Atlantic coast and the Dungeness crab (Cancer magister) of the Pacific coast. In the Indo-Pacific region the swimming crabs (swimming crab), Scylla and Portunus (see photograph—>), related to the American blue crab, are among the most important sources of seafood. Commercially valuable anomurans are the lithodid (literally “stone”) crabs, of which the so-called king crab (Paralithodes camtschatica) found off Japan and in the Bering Sea and Alaskan waters is the most important.

* * *