Real rays

from Wikipedia, the free encyclopedia
Real rays
Crayfish (Raja clavata), juvenile

Crayfish ( Raja clavata ), juvenile

Systematics
Class : Cartilaginous fish (Chondrichthyes)
Subclass : Euselachii
Subclass : Plate gill (Elasmobranchii)
without rank: Stingray (batoidea)
Order : Rajiformes
Family : Real rays
Scientific name
Rajidae
Blainville , 1816

The real rays (Rajidae) are the largest family of rays with 15 genera and almost 180 species .

distribution

Real rays live in all oceans from the Arctic to the Antarctic . Most species live in the temperate seas on mud, sand or gravel bottoms. They are rare in the tropics . They are absent in Polynesia , Hawaii , Micronesia , the Caribbean coast of South America and in coral reefs .

features

The real rays have a rhombic (diamond-shaped), strongly flattened body. The slender, thornless tail is clearly set off. They have weak electrical organs on either side of the tail. The tail is slender, has two side folds and has two reduced dorsal and one small caudal fin. There are species with a pointed and blunt rostrum. The skin is rough covered with small thorns and bumps. The females are usually significantly larger than the males. Shallow water species are light, almost white on the underside. Species from the deep sea are dark on both sides. There are five pairs of gills on the underside. The mouth is straight to curved and has numerous teeth. Real rays eat soil-dwelling organisms. The locomotion takes place through wave-like movements (undulation) of their greatly enlarged pectoral fins.

The best known is the Rajide nail skate ( Raja clavata ), which occurred on European shores of the Black Sea to the Barents lives. The spotted ray ( Raja montagui ) is also common. The common skate ( Dipturus batis ) is now on the IUCN Red List as " Critically Endangered " .

Reproduction

Egg capsule on the beach

In contrast to all other rays that are ovoviviparous (egg-giving birth to life), the real rays lay eggs, which are popularly known as "mermaid bags" or "mermaid bags". The horny egg capsule is rectangular with a thread at each corner. There are slots in the capsule through which the sea water can flow in and supply the embryo with oxygen. You can tell the species from the shape of the eggs . The young rays hatch after 4 to 14 months.

Internal system

The "soft-nosed rays" originally assigned to the real rays as the subfamily Arhynchobatinae are now mostly considered an independent family (→ Arhynchobatidae ), the genera Cruriraja , Fenestraja and Gurgesiella were assigned to the Gurgesiellidae family .

swell

literature

Individual evidence

  1. ↑ a b Last, PR, Weigmann, S. & Yang, L. (2016): Changes to the nomenclature of the skates (Chondrichthyes: Rajiformes). Pages 11 to 34 in Last, PR & Yearsley, GK (Ed.) (2016): Rays of the World : Supplementary information. CSIRO Australian National Fish Collection.
  2. ↑ Kelcie L. Chiquillo, David A. Ebert, Christina J. Slager and Karen D. Crow: The secret of the mermaid's purse: Phylogenetic affinities within the Rajidae and the evolution of a novel reproductive strategy in skates. Mol Phylogenet Evol. 2014 Jun; 75: 245-251. doi: 10.1016 / j.ympev.2014.01.012
  3. ↑ Family Arhynchobatidae on Fishbase.org (English)

Web links

Commons : Real Rays  - Collection of images, videos and audio files