The marine environment contains a diverse group of cartilaginous fish, all sharing a similar flattened body design that often leads to identification confusion. True stingrays belong to the superorder Batoidea, which encompasses over 600 species characterized by having their gill slits on the underside of their bodies. Their distinct appearance features a flattened, disc-shaped body formed by enlarged pectoral fins fused to the head, and a long, often whip-like tail. This successful body plan is mirrored across several related groups, each with its own unique biological adaptations.
Differentiating Skates and Stingrays
Skates and stingrays are the most commonly confused animals sharing this flat, disc-like morphology, yet they possess several key anatomical differences. The distinction lies primarily in their tail structure and defensive mechanisms. Stingrays have a slender, whip-like tail, which typically houses one or more venomous, serrated barbs.
Skates, in contrast, have a thicker, fleshier tail that is not equipped with a stinging spine. Instead of a barb, skates often have small, thorn-like projections (denticles) running along the midline of their back and tail. The pelvic fins also differ, as a stingray’s pelvic fin has only a single lobe, while a skate’s pelvic fin is divided into two distinct lobes.
Reproductive strategy also separates the two groups. Stingrays are viviparous, giving birth to fully formed live young. Skates are oviparous, laying their fertilized eggs in leathery cases often found washed up on shore, commonly referred to as “mermaid’s purses.” While both are bottom-dwellers, skates often feature a more triangular or diamond-shaped disc, while many stingrays display a rounder profile.
Specialized Ray Relatives
Beyond skates, other relatives have evolved specialized features within the flattened body plan. The electric rays, classified in the order Torpediniformes, are recognizable by their thick, soft, and flabby bodies. These rays possess two large, kidney-shaped electric organs located at the base of their pectoral fins.
These organs are composed of modified muscle plaques that generate an electric discharge used to stun prey or deter predators. The voltage produced varies significantly by species, ranging from 8 volts up to 220 volts. Unlike most other rays, electric rays are sluggish and propel themselves using their muscular tail rather than the undulations of their pectoral fins.
Manta and Mobula rays (devil rays) represent the largest and most specialized relatives. These pelagic species are filter feeders, possessing massive, diamond-shaped bodies with wingspans that can exceed 23 feet in the giant oceanic manta ray. Their mouth is positioned at the very front of the head (a terminal mouth), distinct from the bottom-oriented mouth of true stingrays. The most defining feature is the pair of cephalic fins, or “horns,” that extend forward from the head and are used to funnel plankton into their wide mouths.
The Shark-Ray Hybrids
The group of animals sometimes described as “shark-ray hybrids” represents a morphological transition, blending the flattened head of a ray with the elongated body and tail of a shark. The guitarfish (Rhinobatidae) are the most common example of this shape, featuring a shovel-like snout and a body that gradually widens into a flattened disc before narrowing into a robust, shark-like tail.
Guitarfish lack the broad, distinct disc of a true stingray, instead maintaining a relatively thick body through the trunk. They are bottom-dwelling creatures that possess two distinct dorsal fins on their robust tail and, like skates, do not have a venomous barb. Closely related are the wedgefish (Rhinidae), which are generally larger and more robust, sharing the same intermediate body shape. Both are grouped within the order Rhinopristiformes, and their appearance illustrates the evolutionary link between the sharks and the highly flattened ray species.