''Brachynotus sexdentatus'' is a species of

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

in the family

Varunidae The Varunidae are a family of thoracotrematan crabs. The delimitation of this family, part of the taxonomically confusing Grapsoidea, is undergoing revision. For a long time, they were placed at the rank of subfamily in the Grapsidae, but they ap ...

. It is native to 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 north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

and

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...

, and became established for a time in Swansea Docks (

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

). It grows to a maximum

carapace A carapace is a Dorsum (biology), 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 tor ...

width of , and lives in shallow water on muddy bottoms.

Description

''Brachynotus sexdentatus'' is a small crab, reaching a maximum

width of , but typically less than . The front of the carapace has two lobes and three lateral teeth on each side, each ending in a sharp point. The whole animal is

olive green Olive is a dark yellowish-green color, like that of unripe or green olives. As a color word in the English language, it appears in late Middle English. Shaded toward gray, it becomes olive drab. Variations Olivine Olivine is the typical ...

, with speckling in black, with the legs slightly paler or greyer. The claws are of similar side on either side of the body, but are much larger in males than in females.

Ecology and life cycle

''Brachynotus sexdentatus'' lives in shallow water on muddy bottoms, at depths of up to . The eggs of ''B. sexdentatus'' are in diameter, and dark brown in colour. They are produced between February and October. After hatching, the

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

of ''B. sexdentatus'' pass through five zoeal stages (instars that use appendages of the thorax for movement). This process takes at least 12 days at a temperature of , during which time the larvae grow from around from the tip of the rostrum to the tip of the dorsal spine, to long (

length). After a further five days, the larva moults into the megalopa phase (instar that uses the appendages of the abdomen for movement), and after five more days, moults into the first crab-like phase, at a carapace length of around .

Distribution

''Brachynotus sexdentatus'' is native to the

, from

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

, and the

coasts of

Romania Romania ( ; ro, România ) is a country located at the crossroads of Central Europe, Central, Eastern Europe, Eastern, and Southeast Europe, Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, S ...

and

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...

. It is also found in the

Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...

, having entered the canal's northern end before 1927, and was discovered in 1957 in the Queen's Dock,

Swansea Swansea (; cy, Abertawe ) is a coastal city and the second-largest city of Wales. It forms a principal area, officially known as the City and County of Swansea ( cy, links=no, Dinas a Sir Abertawe). The city is the twenty-fifth largest in ...

, presumably having been transported by shipping from the Mediterranean Sea. This site was artificially warmed by the adjacent Tir John

coal-fired power station A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide, there are about 8,500 coal-fired power stations totaling over 2,000 gigawatts Nameplate capacity, capacity. They ...

, which used sea-water as its coolant, drawing it in from the King's Dock, and expelling it into the Queen's Dock. In 1976, the power station closed, ending the transport of

waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...

into the Queen's Dock, and the population of ''B. sexdentatus'' died out soon after.

Taxonomy

''Brachynotus sexdentatus'' was first described by Antoine Risso in 1827, as a species in the genus ''

Goneplax ''Goneplax'' is a genus of crabs, containing the following extant species: *'' Goneplax barnardi'' (Capart, 1951) *'' Goneplax clevai'' Guinot & Castro, 2007 *''Goneplax rhomboides'' (Linnaeus, 1758) *'' Goneplax sigsbei'' (A. Milne-Edwards, 1880 ...

''. Wilhem de Haan described the new genus '' Brachynotus'' in 1833, and ''B. sexdentatus'' was eventually designated its

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

. ''Brachynotus gemmellari'' has in the past been treated as a

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

of ''B. sexdentatus'', and the population from Swansea Docks was originally identified as "''B. sexdentatus gemmellari''". It is now treated as a full species, although the Swansea population may represent ''B. sexdentatus'' (''

sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...

''). Although later opinions place the Swansea specimens in ''B. gemmellari'' rather than ''B. sexdentatus'', they also showed that the two species are indistinguishable from DNA sequences at the

16S ribosomal DNA 16 S ribosomal RNA (or 16 S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as 16S rRNA ...

locus, and may either be very recently separated or may be experiencing high levels of

gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...

References

{{Taxonbar, from=Q4953493 Grapsoidea Crustaceans of the Atlantic Ocean Fauna of the Mediterranean Sea Crustaceans described in 1827