''Goneplax rhomboides'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

. It is known by the

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

angular crab because of its angular

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

. Although it is also called the ''square crab'', its shell is in fact more

trapezoidal In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

than

square In geometry, a square is a regular polygon, regular quadrilateral. It has four straight sides of equal length and four equal angles. Squares are special cases of rectangles, which have four equal angles, and of rhombuses, which have four equal si ...

(or

rhomboidal Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are non-right angled. The terms "rhomboid" and "parallelogram" are often erroneously conflated with each oth ...

, as its

scientific name In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

might suggest). This species is also known as the '' mud-runner'' because they are able to run away quickly when threatened.

Description

''Goneplax rhomboides'' is a relatively small (carapace up to in diameter), distinctive-looking crab that ranges from yellowish-white, to orange, to reddish to vivid pink in colour. It has a smooth, quadrangular, strongly convex carapace that is much broader than it is long. It has long, slender

pereiopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...

s with margins of propodus and dactylus

bristles A bristle is a stiff hair or feather (natural or artificial), either on an animal, such as a pig, a plant, or on a tool such as a brush or broom. Synthetic types Synthetic materials such as nylon are also used to make bristles in items such as b ...

. It likewise has

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e on its antennae and mouthparts. Females have short

cheliped A chela ()also called a claw, nipper, or pinceris a pincer-shaped organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through Neo-Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds ...

s but the chelipeds of males are long, with the merus portion of the claw considerably longer than the length of their carapace. ''G. rhomboides'' has often been confused with '' G. clevai'', a similar species sharing at least part of its range. Its eyes are on the end of long, retractable eyestalks.

Distribution and habitat

''G. rhomboides'' is found in the northeastern

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

and the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

from the

North Sea The North Sea lies between Great Britain, Denmark, Norway, Germany, the Netherlands, Belgium, and France. A sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian Se ...

to southern

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and the

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

coast of

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. Waters off

Shetland Shetland (until 1975 spelled Zetland), also called the Shetland Islands, is an archipelago in Scotland lying between Orkney, the Faroe Islands, and Norway, marking the northernmost region of the United Kingdom. The islands lie about to the ...

constitute the northern boundary of its range, and in 2008,

marine biologists Marine biology is the scientific study of the biology of marine life, organisms that inhabit the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology clas ...

from the

University of Gothenburg The University of Gothenburg () is a List of universities in Sweden, university in Sweden's second largest city, Gothenburg. Founded in 1891, the university is the third-oldest of the current List of universities in Sweden#Public universities, S ...

discovered one intact in the stomach of a

cod Cod (: cod) is the common name for the demersal fish genus ''Gadus'', belonging to the family (biology), family Gadidae. Cod is also used as part of the common name for a number of other fish species, and one species that belongs to genus ''Gad ...

caught off the coast of

Bohuslän Bohuslän () is a Provinces of Sweden, Swedish province in Götaland, on the northernmost part of the country's west coast. It is bordered by Dalsland to the northeast, Västergötland to the southeast, the Skagerrak arm of the North Sea to the ...

which suggests that ''G. rhomboides'' has now moved into Swedish waters. A similar discovery a few weeks later in the same location reinforces this conclusion. This species inhabits

mud Mud (, or Middle Dutch) is loam, silt or clay mixed with water. Mud is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone (generally cal ...

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s similar to those favoured by the

Norway lobster ''Nephrops norvegicus'', known variously as the Norway lobster, Dublin Bay prawn, ' (compare langostino) or ''scampi'', is a slim, coral-colored lobster that grows up to long, and is "the most important commercial crustacean in Europe". It is ...

and burrows into inshore muddy sand. Its burrows often interconnect in complex patterns with those inhabited by other species of burrowing

megafauna In zoology, megafauna (from Ancient Greek, Greek μέγας ''megas'' "large" and Neo-Latin ''fauna'' "animal life") are large animals. The precise definition of the term varies widely, though a common threshold is approximately , this lower en ...

such as '' Callianassa subterranea'', '' Cepola macrophthalma'', '' Lesueurigobius friesii'', and ''

Nephrops norvegicus ''Nephrops norvegicus'', known variously as the Norway lobster, Dublin Bay prawn, ' (compare langostino) or ''scampi'', is a slim, coral-colored lobster that grows up to long, and is "the most important commercial crustacean in Europe". It is ...

''. These multi-species burrow complexes are very common in some localities.

Symbiosis

The setae on the antennae, mouthparts and legs of ''G. rhomboides'' are home to '' Triticella flava'', a species of

Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

("moss animal"). The short lifespan of these

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

moss animals is synchronized so that they produce larvae just before ''G. rhomboides'' moults. These larvae then attach to the crab's newly emerged

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

References

External links

* {{Portal bar, Crustaceans, Marine life Goneplacoidea Crabs of the Atlantic Ocean Crustaceans described in 1758 Taxa named by Carl Linnaeus