Stingrays, with their unique flattened bodies, often lead to questions about their connection to sharks. While they appear quite different, there is a shared biological heritage that links these fascinating creatures. Understanding their classification helps clarify how they fit into the broader aquatic world.
A Shared Ancestry
Stingrays are not part of the shark family, but they are closely related. Both belong to the class Chondrichthyes, which encompasses all cartilaginous fish. Their skeletons are primarily composed of flexible cartilage rather than bone, a defining characteristic of this group. Within Chondrichthyes, both sharks and rays are classified under the subclass Elasmobranchii, meaning “plate gills”.
Common Traits
Sharks and stingrays share several biological features due to their elasmobranch classification. They typically possess five to seven pairs of gill slits that open individually to the exterior, although their placement differs between sharks and rays. Both also have placoid scales, also known as dermal denticles, which give their skin a rough, sandpaper-like texture.
Another shared trait is the absence of a swim bladder, an organ common in bony fish for buoyancy control. Instead, elasmobranchs regulate buoyancy largely through large livers rich in oil. Furthermore, they possess specialized sensory organs called Ampullae of Lorenzini, which detect electrical fields produced by other organisms, aiding in prey detection. This sophisticated sense helps them navigate and hunt.
Distinctive Features
Despite their shared ancestry, stingrays and sharks exhibit clear differences. Stingrays generally have flattened, disc-like bodies, while sharks have a more streamlined, torpedo-shaped form. Stingray gill slits are on their ventral (underside) surface, whereas sharks have theirs laterally (on their sides). Stingrays also have a ventral mouth for bottom feeding, unlike the subterminal or terminal mouths of sharks.
Their pectoral fins differ notably; in stingrays, these fins are enlarged and fused to the head, forming the distinctive “wings” of their disc. Sharks have distinct, separate pectoral fins. Many stingrays are benthic, inhabiting and feeding on the seafloor, often burying themselves in sand. Sharks, while some are bottom-dwellers, often occupy pelagic (open-water) habitats. Many stingray species also possess venomous barbs on their tails, a feature absent in sharks.
Wider Elasmobranch Family
Beyond sharks and stingrays, the subclass Elasmobranchii includes other cartilaginous fish, such as skates and sawfish. Skates share the flattened body shape of stingrays but generally lack the venomous tail barb and have a thicker tail. They also differ in reproduction, with skates laying leathery egg cases known as “mermaid’s purses,” while most stingrays give birth to live young.
Another group of cartilaginous fish, chimaeras, belong to a different subclass called Holocephali, though still within the larger class Chondrichthyes. Chimaeras, also known as ghost sharks, possess a gill cover and their upper jaw is fused to their skull, unlike elasmobranchs. These diverse groups highlight the variety within cartilaginous fish.