''Stenorhynchus seticornis'', the yellowline arrow crab or simply arrow crab, is a

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

of marine crab.

Description

The body of ''S. seticornis'' is triangular, and the

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

is drawn out into a long point with serrate edges. The legs are also long and thin, up to across, and the animal's

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 und ...

may be up to long. Colouration is variable in this species; the body may be golden, yellow or cream, marked with brown, black or

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

-blue lines; the legs are reddish or yellow, and the

claw 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 ...

s are blue or violet. This species presents as diagnostic features: triangular body with long pointed snout (rostrum), carapace decorated with fine dark lines and claws often have violet tips. ''S. seticornis'' is most commonly associated with anemones, in groups ranging from one to six individuals in south-eastern Brazil.

Distribution

''Stenorhynchus seticornis'' is commonly found in the shallow sub-tidal on rock bottoms, corals, calcareous algae, and also on soft sediments, such as shelly gravel and sand. Its geographical distribution is restricted to the Occidental Atlantic, from North Carolina to Argentina. ''Stenorhynchus seticornis'' is found in the western

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...

, from

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia a ...

and

Bermuda ) , anthem = " God Save the King" , song_type = National song , song = "Hail to Bermuda" , image_map = , map_caption = , image_map2 = , mapsize2 = , map_caption2 = , subdivision_type = Sovereign state , subdivision_name = , ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, including throughout the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

,. It lives on

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

s at depths of .

Ecology and behaviour

''S. seticornis'' is

nocturnal Nocturnality is an ethology, animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatures generally have ...

and

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or an ...

. It eats small feather duster worms and other coral reef

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. This crab is commonly kept in reef aquariums to control

bristle worm 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 ...

populations. ''S. seticornis'' is one of a number of different

s that are found living in association with the sea anemone, ''

Lebrunia danae ''Lebrunia neglecta'' is a species of sea anemone in the family Aliciidae. It is found in the Caribbean Sea and Gulf of Mexico. Description ''Lebrunia neglecta'' is an unusual sea anemone in that its tentacles are almost hidden by the ring of ...

''. It is often found among the anemone's pseudotentacles along with Pederson's cleaning shrimp (''

Ancylomenes pedersoni ''Ancylomenes pedersoni'', sometimes known as Pederson's shrimp and Pederson's cleaner shrimp, is a species of cleaner shrimp. It is part of the genus ''Ancylomenes'' and was described in 1958 by Fenner A. Chace Jr. as ''Periclimenes pedersoni''. ...

'') and the spotted cleaner shrimp (''

Periclimenes yucatanicus The spotted cleaner shrimp (''Periclimenes yucatanicus''), is a kind of cleaner shrimp common to the Caribbean Sea. These shrimp live among the tentacles of several species of sea anemones. They sway their body and wave their antennae in order to ...

''). ''S. seticornis'' have displayed notable negative phototaxis, meaning the organism prefers to avoid sunlight. This species changes location during the day and nighttime.

Symbiotic Relationships

There is a considerable number of reports on cleaning symbiosis among reef fish, moray eels, and squirrelfish. This is a somewhat unexpected relationship as moray eels and squirrelfish can be considered dangerous clients, because crabs are important elements of their diets. This behavior has only been observed in the natural environment in Brazilian waters but it is believed that this behavior also exists throughout its distribution.

Life cycle & Reproduction

During

mating In biology, mating is the pairing of either opposite- sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. '' Copulation'' is the union of the sex organs of two sexually rep ...

, the male places a

spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...

on the female, which she uses to

fertilise Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Pro ...

her

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

. These fertilised eggs are then carried on the female's

pleopod The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...

s until they are ready to hatch into

zoea Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The ...

larvae. These swim towards the ocean surface and feed on

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

. They grow through a series of moults, and eventually metamorphose into the adult form. When mature, the spermatozoa of ''S. seticornis'' show five lateral arms, similar to the sperm morphology of ''Inachus phalangium.''

Breeding Period

Climate majorly regulates the breeding period of the arrow crab. Seasonal variation of water temperature and sunlight duration are considered as the most important variables determining the breeding period of arrow crabs. There is a positive relationship between fecundity and the size of the parental female. In fact, the size of the female is the key variable in determining the number of eggs per batch. The female also determines the reproductive output of arrow crabs.

Larval Stage

Larvae that have grown in shallow water differ from larvae that grow in deeper water. The key difference is in the setation of the endopodite of the maxilla.

Taxonomic history

''Stenorhynchus seticornis'' was first described by

Johann Friedrich Wilhelm Herbst Johann Friedrich Wilhelm Herbst (1 November 1743 – 5 November 1807) was a German naturalist and entomologist from Petershagen, Minden-Ravensberg. He served as a chaplain in the Prussian army. His marriage in Berlin, 1770, with Euphrosyne Luis ...

in 1788, under the name ''Cancer seticornis''. It was also described as "''Cancer sagittarius''" by

Johan Christian Fabricius Johan Christian Fabricius (7 January 1745 – 3 March 1808) was a Danish zoology, zoologist, specialising in "Insecta", which at that time included all arthropods: insects, arachnids, crustaceans and others. He was a student of Carl Linnaeus, an ...

in 1793, a name which is now a junior synonym of ''S. seticornis''.

Pierre André Latreille Pierre André Latreille (; 29 November 1762 – 6 February 1833) was a French zoology, zoologist, specialising in arthropods. Having trained as a Roman Catholic priest before the French Revolution, Latreille was imprisoned, and only regained hi ...

erected the genus ''

Stenorhynchus ''Stenorhynchus'' is a genus of marine crabs in the family (biology), family Inachidae, containing the following species: *''Stenorhynchus debilis'' (S. I. Smith, 1871) *''Stenorhynchus lanceolatus'' (Brullé, 1837) *''Stenorhynchus seticornis'' ...

'' (originally mis-spelt ''Stenorynchus'') in 1818, and ''S. seticornis'' was confirmed as the

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( ...

by the

International Commission on Zoological Nomenclature The International Commission on Zoological Nomenclature (ICZN) is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 26 commissioners from 20 countries. Orga ...

in 1966.

References

External links

* * {{Taxonbar, from=Q3001943 Majoidea Crustaceans of the Atlantic Ocean Crustaceans described in 1788