Uncover the similarities and differences that set sharks and rays apart.
Sharks and rays are from the same family known as elasmobranchs and there are over 1,100 known species of elasmobranchs in our oceans. That’s over 500 sharks, and over 600 rays, say the experts at The Shark Trust.
Elasmobranchs are a subclass of ‘Chondrichthyes’ and have cartilaginous, rather than bony, skeletons. They exhibit a vast diversity of shapes, sizes and adaptations, unique to each species.
Here, we unravel the differences between the sharks and the rays, and how to tell them apart.
Which came first, the shark or the ray?
From an evolutionary perspective, the sharks came first, having been around for over 400 million years. Rays diverged from them only around 200 million years ago.
It is believed that rays evolved from sharks that had adapted well to the sandy, muddy sediments of shallow coastal slopes during the Jurassic Period. Their bodies flattened out, their pectoral fins became enlarged and in many of them, the tail area was reduced.
Some (mobulids and mantas) developed cephalic lobes (fleshy projections on the side of their heads), covered in electrosensory pores to help when hunting. Others developed a sting in their tail; their modified tails having become superfluous to movement evolved into a defence mechanism, while some adapted to fresh water, living in rivers and lakes around the world.
What’s the difference between sharks and rays?
When comparing most species of sharks and rays, the most pronounced difference is usually the torpedo or flat shape of their bodies. However, this distinction can become misleading when, for instance, comparing Angel Sharks and Guitarfish.
Both are flat-bodied species, but one is a shark and the other a ray. One key, reliable difference between sharks and rays is the gill placement: among rays, the gills are located on the underside of the body, whilst in sharks they are located on either side of their head.
The evolution of the flattened, disc-like bodies of rays has engendered many other advantageous adaptations, which separate them from sharks:
How do sharks and rays ‘breathe’?
Many species of sharks are known as ‘ram ventilators’, meaning they have to keep moving in order to get oxygen through their gills. All rays have evolved special organs called ‘spiracles’ which allow them to flush water through their gills even when buried under the sand, in order to continuously receive oxygen when stationary or covered up.
How do sharks and rays swim through the water?
All sharks swim using continuous side to side undulations their body. This creates the classic swimming motion that we know as they glide forward through the water column.
In contrast, most rays use one of two movement options, undulatory or oscillatory movement. Undulatory swimmers pass short waves down the pectoral fins. In contrast, oscillatory swimmers ‘flap’ their pectoral fins to push themselves forward, similar to a bird wing flapping.
What about rays and skates – what’s the difference between them?
There is often some confusion around skates and rays, so whilst we’re on the topic of differences, we thought we’d clear this up too.
Put simply, all skates are rays but not all rays are skates. In other words, rays are the umbrella for many species and families of rays – one of which are the skates.
Visually, the easiest way to tell a skate from a ray is by looking at their tail. Skates tend to have shorter and thicker tails whilst rays tend to have thinner, more whip-like tails, often with a stinging spine. Skates and rays also differ in their reproductive modes: all rays give birth to live young, whereas all skates lay eggs or mermaid’s purses. And to add to the confusion, we have, over time, gradually accepted incorrect common names for various species of skate and ray. For instance, we say the Thornback Ray (Raja clavata), although it is technically a skate.
There is a beautiful diversity of sharks, skates and rays in our oceans, each with their own unique adaptations and curiosities. We haven’t even touched on chimaera, their other close relative. Unfortunately, the sobering truth is that over a third of all sharks, rays and chimaera are at risk of extinction due to overfishing.
About the Shark Trust
The Shark Trust is a UK-based charity that works tirelessly to safeguard the future of sharks, and their close cousins, the skates and rays, around the world. They have a vision: A future where sharks thrive within a globally healthy marine ecosystem. Established in 1997 to provide a voice for sharks, the Shark Trust has an ever-growing number of passionate supporters and together they’re creating positive change for sharks around the world.