The thornback ray (''Raja clavata''), or thornback skate, is a species of

ray fish Batomorphi is a division of cartilaginous fishes, commonly known as rays, this taxon is also known as the superorder Batoidea, but the 5th edition of ''Fishes of the World'' classifies it as the division Batomorphi. They and their close relativ ...

in the family Rajidae.Fishbase.org: ''Raja clavata''
/ref>

Distribution

The Thornback ray is found in the Atlantic

coastal A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

waters of Europe and western Africa. It is also present from South Africa to the southwestern Indian Ocean and in the Mediterranean and Black Seas. It is native possibly as far south as Namibia and South Africa. Its natural

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 are open large

sea A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...

s and shallow seas. It is sometimes seen trapped in large

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

pools at low tide. The thornback ray is probably one of the most common rays encountered by divers.

Habitat

The thornback ray is usually found on sedimentary seabeds such as mud, sand or gravel at depths between 10–60m. Juvenile fish feed on small

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, particularly

amphipod Amphipoda () is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphipod species cur ...

s and bottom-living

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

s; adults feed on

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 ...

s, shrimps and small fish.

Description

Like all rays, the thornback ray has a flattened body with broad, wing-like

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s. The body is kite-shaped with a long, thorny tail. The back is covered in numerous thorny spines, as is the underside in older females. Adult fish can grow to in length, although most are less than . This ray can weigh from 4.5 to 8.75 lb (2 to 4 kg). Their colours vary from light brown to grey with darker blotches and numerous small darker spots and yellow patches. Sometimes the yellow patches are surrounded by small dark spots. The underside is creamy-white with a greyish margin. When threatened they can appear black.Oceanario.pt: ''Raja clavata''
/ref> In sexually mature fish, some of the spines are thickened with button-like bases (known as bucklers). These are particularly well developed on the tails and backs of sexually mature females.

Taxonomy

''Raja clavata'', the thornback ray (or thornback skate, roker), was named by

Carl Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

in the

10th edition of Systema Naturae The 10th edition of ''Systema Naturae'' (Latin; the English title is ''A General System of Nature'') is a book written by Swedish naturalist Carl Linnaeus and published in two volumes in 1758 and 1759, which marks the starting point of zoologic ...

in 1758, in the genus

Raja Raja (; from , IAST ') is a noble or royal Sanskrit title historically used by some Indian subcontinent, Indian rulers and monarchs and highest-ranking nobles. The title was historically used in the Indian subcontinent and Southeast Asia. T ...

'' of the

Order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Rajiformes Rajiformes is one of the four Order (biology), orders in the clade Batomorphi, often referred to as the superorder Batoidea, flattened cartilaginous fishes related to sharks. Rajiforms are distinguished by the presence of greatly enlarged pector ...

in the Family Rajidae. It is one of about 13 species of

skate Skate or Skates may refer to: Fish *Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongin ...

(family Rajidae) that are known 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 ...

and adjacent Atlantic waters.

Common names

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 include: * Danish — Sømrokke. * Dutch — Stekelrog. * English — Roker / Thornback ray / Dorn. * Estonian — Astelrai. * Faeroese — Naglaskøta. * Finnish — Okarausku. * French — Raie bouclée. * German — Nagelrochen. * Icelandic — Dröfnuskata. * Latvian — Dzelkņraja. * Norwegian — Piggskate. * Polish — Raja nabijana a. ciernista. * Portuguese — Raia lenga / Raia brocheada * Russian — Колючий скат. * Spanish — Raya de clavos. * Swedish — Knaggrocka.

Morphometrics

Dorsal spines : 0; Anal spines: 0; Anal soft rays: 0. ; disc-width 1,25 to 1,36 times in its length, its length 1,70 to 1,83 times in total length; pectoral fins with clear angles on lateral side; triangular pelvic fins. Dorsally prickly; large females also prickly throughout their ventral surface; young and large males prickly along the borders of their discs and the underside of their snout. 30–50 thorns form a median row from the nape to the first dorsal fin; additional large 'buckler' thorns with swollen bases scattered on upper surface of disc in adults. Max length : 105 cm male/unsexed; 139.0 cm (female); common length : 85.0 cm; max. weight: 18.0 kg. Thornback ray on a white background

Life cycle

Thornback rays are an

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

and

polyandrous Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives ...

species. Paired eggs are laid and deposited on shallow sand, mud, pebble or gravel bottoms . Up to 170 egg cases can be laid by a single female in a year, average fecundity around 48–74 eggs. In northwestern Europe, egg cases are laid during spring, and in the Mediterranean during winter and spring. Egg cases are oblong capsules with stiff pointed horns at the corners, each containing one embryo. Capsules are 5.0–9.0 cm long without the horns and 3.4–6.8 cm wide. Egg cases are anchored with an adhesive film. Embryos feed solely on yolk. Egg cases hatch after about 4–5 months and pups are about 11–13 cm. Mating season is from February to September, peaking in June. Adults observed to form same-sex aggregations during the mating season with females moving to shallower inshore waters approximately a month before the males. Mating does not occur in the Baltic Sea. This is one of the fish used by the marine leech '' Pontobdella muricata'' as a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

. ;British Isles population Nagelrochen nhm

A search about the growth and maturation of ''Raja clavata'' in the

Solway Firth The Solway Firth is an inlet on the west coast of Great Britain, forming part of the border between England and Scotland. The firth (a Scottish term for an inlet of the sea) divides Cumbria (including the Solway Plain) from Dumfries and Gallow ...

(part of the border between

Cumbria Cumbria ( ) is a ceremonial county in North West England. It borders the Scottish council areas of Dumfries and Galloway and Scottish Borders to the north, Northumberland and County Durham to the east, North Yorkshire to the south-east, Lancash ...

, England and

Dumfries and Galloway Dumfries and Galloway (; ) is one of the 32 unitary council areas of Scotland, located in the western part of the Southern Uplands. It is bordered by East Ayrshire, South Ayrshire, and South Lanarkshire to the north; Scottish Borders to the no ...

, Scotland) shows that the males and females appear to mature at 42 and 45 cm in disc width respectively. The Solway population is heavily exploited by an unrestricted commercial fishery and a considerable proportion (48.6%) of the retained catch is immature. It is suggested that fishing pressure has brought about a reduction in the size at which female fish mature.

References

* Picton, B.E. & Morrow, C.C., 2005. — ''Encyclopedia of Marine Life of Britain and Ireland''.
Habitas.org.uk: ''Raja clavata'' (Thornback ray)

External links

*
Fishbase.org Database: ''Raja clavata'' IUCN Red List of all current Threatened Species
* {{Authority control

thornback ray The thornback ray (''Raja clavata''), or thornback skate, is a species of ray (fish), ray fish in the family Rajidae. Distribution The Thornback ray is found in the Atlantic coastal waters of Europe and western Africa. It is also present from ...

Fish of the East Atlantic Fish of the Mediterranean Sea Fish of the North Sea Near threatened biota of Africa Near threatened biota of Europe

Taxonomy articles created by Polbot