CLASSIFICATION of SKATE : RAJA
Phylum :- CHORDATA ( Notochord and dorsal tubular nerve cord present and gill-slits present).
Group :- CRANIATA ( Cranium with brain present ).
Subphylum :- VERTEBRATA (Vertebral column present ).
Division :- GNATHOSTOMATA ( Jaws and paired appendages present ).
Super class :- PISCES (Paired fins , gills and skin with scales)
Class :- CHONDRICHTHYES { =ELASMOBRANCHI } (Endoskeleton cartilaginous. Scales usually placoid. spiral valve in intestine ).
Sub-class :- SELACHI (Sharks and rays. Gills in seperate clefts. Cloaca present).
Order :- HYPOTREMATA { = BATOIDAE } (Gills-slits ventral. spiracles present. dorsal fin on tail, if present)
Family :- RAJIDAE (Pectoral fin elongated and joined to sides of the body).
Genus :- Skate : Raja
GEOGRAPHICAL DISTRIBUTION
Raja : Skate is found in almost all the temperate sea waters. Most of the species belonging to the genus Raja are abundantly distributed in northern hemisphere, Arctic and Antarctic regions.
HABIT AND HABITAT
Raja is marine, sluggish, bottom-dwelling, carnivorous, feeding on small and crustaceans,, They catch their prey by dropping over them and covering prey from all sides from their body and fins.
GENERAL CHARACTERSTICS OF SKATE : RAJA
- Commonly known as skate measuring 2 to 3 metres in width.
- A large portion of the skate’s dorsal body is covered by rough skin made of placoid scales.
- Placoid scales have a pointed tip that is oriented caudally and are homologous to teeth. Their mouths are located on the underside of the body, with a jaw suspension common to Batoids known as euhyostyly
- Body is dorsoventrally flattened, rhomboidal and differentiated into anterior rhombic disk and slender tail.
- Colouration of upper surface resembles with sandy or gravelly environment of bottom. Skin slender and provided with spines. Body divided into head, trunk and tail.
- Disc is made up by the head, trunk and confluent pectoral fins. There are rows of tiny spines over the disc and a median row over the tail.
- Head produced in a short snout with a pair of dorsal eyes. Spiracles are found just below the eyes.
- Ventral mouth provided with numerous sharp, rasping teeth for tearing the prey. Slender tail distinctly demarcated from the rhombic disk.
- Fins-paired pectoral and pelvic fins present. First dorsal fin and second dorsal fins near caudal fins.
- skate anatomy is similar to other Batoidea, features such as their electric organ and mermaid’s purse create clear distinctions.
- Sexually dimorphic. Male is provided with a pair of claspers near the pelvic fin. Oviparous, egg capsules four-horned.
SPECIAL FEATURES
The pectoral fins are greatly expanded. They are endoskeletal supported and they extend along the lateral margins of the trunk from the pelvic fins upto the snout. Tail contains one median and two additional rows of small spines which inflict severe and irritating wound.
IDENTIFICATION
Since this fish has rhomboid disk, fused pectoral fins and above features, hence it is Raja or Skate.
REFERENCES
- https: // en.wikipe dia.org /wiki/Skate_(fish)
- https : // www.sciencedirect.com/ topics/biochemist ry-genetics-and- molecular- biology/skate-fish
- Book of Practical Zoology VERTEBRATE by S.S.LAL – Rastogi Publications.
- https : // www.britannica.com/ animal/ skate-fish
- SOURCES OF IMAGES – https://www.google.com/url?sa=i&url=https%3A% 2F%2Fwww.pinter est.com%2Fpin%2 F47414466699910 0716%2F&psig=A OvVaw0rvOrPbM A-Zbr XdKNPRKUq&ust= 1602651285473000 & source=images&cd= vfe&ved=2ahUKEwi y1Om147DsAhUNG3IKHbe8Cj8Qr4kDegUIARDgAQ
- https://www.goog le.com/url? sa=i&url=https%3 A%2F%2Fwww.br itannica.com%2Fanimal%2Fskate- fish&psig=AOvVa w0rvOrPbMA- ZbrXdKNPRKUq &ust=1602651285 473000&source=i mages&cd=vfe&ve d=2ahUKEwiy1O m147DsA hUNG3I KHbe8Cj8 Qr4kDe gUIARDcA Q
- https: // www.goog le.com/ url? sa=i&url=https%3 A%2F%2Foceana. org%2Fmarine- life%2Fsharks- rays%2Fbarndoor- skate&psig=AOvV aw0rvOrPbMA- ZbrXdKNPRKUq &ust=1 602651285 47 3000&source=i m ages&cd=vfe&ve d=2ahUKE wiy1O m14 7D sAhU NG3I KHbe8C j8Qr 4kDe gUI ARC BAg
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