''Polybius henslowii'' is a species of

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 ...

, the only species in the genus Polybiidae. It is a capable swimmer and feeds in open water in the north-east

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 western

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 ...

Description

The

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 ...

of ''Polybius henslowii'' is almost circular, wide and long. The first pair of

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 (walking legs) carry

claws A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tars ...

, and the remaining four pairs are flattened with fringed edges. This contrasts with other members of the family

Portunidae Portunidae is a family of crabs which contains the swimming crabs. Its members include well-known shoreline crabs such as the blue crab (''Callinectes sapidus'') and velvet crab ('' Necora puber''). Description Portunid crabs are characterised b ...

, which have only the last pair of legs adapted for swimming. ''P. henslowii'' is red-brown on the upper surface, and paler beneath.

Distribution

''Polybius henslowii'' is found in the northeast

from the

British Isles The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

, and in the western

. Very abundant swarms have been found along the coasts off

Galicia (Spain) Galicia ( ; or ; ) is an Autonomous communities of Spain, autonomous community of Spain and nationalities and regions of Spain, historic nationality under Spanish law. Located in the northwest Iberian Peninsula, it includes the provinces o ...

and off

Portugal Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...

. Rare specimens have been caught in 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 ...

east of

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 ...

, and in the

Skagerrak The Skagerrak (; , , ) is a strait running between the North Jutlandic Island of Denmark, the east coast of Norway and the west coast of Sweden, connecting the North Sea and the Kattegat sea. The Skagerrak contains some of the busiest shipping ...

. Its range has expanded into the southern North Sea, possibly as a result of

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

. It can be found on

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

y or

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

ly sediments at depths of up to .

Ecology and behaviour

''Polybius henslowii'' is a capable swimmer and can be found swimming near the ocean surface, where it feeds on a mixture of

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

, fish, and other crustaceans, including specimens of the same species. ''P. henslowii'' has been observed to form

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

swarms. These swarms are mostly composed of females, excluding that aggregations are for mating, while they might be related to feeding. When they swim inshore, along the coastal upwelling areas of Galicia (NW Spain), they rely more on benthic prey, such as

polychaetes Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...

and detritus and are influenced by terrestrial organic matter coming from the rivers. In Galicia (NW Spain), ''P. henslowii'' is an important food source for the yellow-legged gull, '' Larus michahellis''. In summer,

loggerhead turtle The loggerhead sea turtle (''Caretta caretta'') is a species of oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around in carapace length when ful ...

s (''Caretta caretta'') off

North Africa North Africa (sometimes Northern Africa) is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region. However, it is sometimes defined as stretching from the Atlantic shores of t ...

feed almost exclusively on ''P. henslowii''.

Taxonomy

''Polybius henslowii'' was first described by

William Elford Leach William Elford Leach (2 February 1791 – 25 August 1836) was an English zoologist and marine biologist. Life and work Elford Leach was born at Hoe Gate, Plymouth, the son of an attorney. At the age of twelve he began a medical apprenticesh ...

in 1820, originally as the only species in his new genus ''Polybius''. The genus name "''Polybius''" may be in reference to the Greek historian

Polybius Polybius (; , ; ) was a Greek historian of the middle Hellenistic period. He is noted for his work , a universal history documenting the rise of Rome in the Mediterranean in the third and second centuries BC. It covered the period of 264–146 ...

; the

specific epithet 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 ...

' honours

John Stevens Henslow John Stevens Henslow (6 February 1796 – 16 May 1861) was an English Anglican priest, botanist and geologist. He is best remembered as friend and mentor to Charles Darwin. Early life Henslow was born at Rochester, Kent, the son of a solicit ...

, Professor of Botany at Cambridge University, who had collected the specimens used by Leach from a herring fisherman in

North Devon North Devon is a Non-metropolitan district, local government district in Devon, England. Its council is based just outside Barnstaple, the district's largest town. The district also includes the towns of Ilfracombe, Lynton and Lynmouth and Sout ...

in 1817. This was the first of several species that were named in Henslow's honour.

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 ...

s for the species include "sardine swimming crab" and "Henslow's swimming crab".

References

{{Taxonbar, from1=Q3934386, from2=Q1990508 Portunoidea Crabs of the Atlantic Ocean Crustaceans described in 1820