Skate (fish)
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Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. More than 150 species have been described, in 17 genera. Softnose skates and pygmy skates were previously treated as subfamilies of Rajidae, but are now considered as distinct families. Alternatively, the name "skate" is used to refer to the entire order of Rajiformes.
Full view of a skate's mermaid's purse. Roughly 125 mm in length.
A skate laying an egg case (mermaid's purse) at the San Sebastian Aquarium
Four developing embryos located in an opened big skate egg case (mermaid's purse)
Fish fin
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Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the spine and are supported only by muscles.
Dorsal fin of a chub (Squalius cephalus)
Skeleton of a lingcod, a ray-finned fish
Lobe-finned fishes, like this coelacanth, have fins that are borne on a fleshy, lobe-like, scaly stalk extending from the body. Due to the high number of fins it possesses, the coelacanth has high maneuverability and can orient its body in almost any direction in the water.
Pectoral fin with fleshy lobe of Latimeria chalumnae (Citron / CC-BY-SA-3.0)