Rays are unlike any other animals—their flat bodies and flapping “wings” give them one of the most distinctive silhouettes in the ocean. But with hundreds of species of ray, these critters can be difficult to tell apart. Today, we’re here to help you differentiate between two commons types of ray: stingrays and skates.

To start, let’s look at what they have in common. Stingrays and skates are both elasmobranchs, meaning they are cartilaginous fish whose skeleton is made of cartilage instead of bone. They have some pretty famous relatives: sharks are also elasmobranchs! Both are part of a superorder (for the taxonomy buffs, this means a category that is larger than an order, but not quite a class) called Batoidea. All of the animals within this category are considered “rays”, and it includes well over 600 species.

At first glance, stingrays and skates look similar. They both have flat bodies that look like a kite and move by undulating their large wing-like pectoral fins. Their gill slits are on the ventral (underside) of their body (in sharks, for example, these slits are located on the sides of their heads). They are also largely found on the sea floor, where they can lay flat against the sand and hide from predators and sneak up on prey.

Although these animals are closely related, they’re definitely not the same. Stingrays fall in the order Myliobatformes, where skates are in the order Rajiformes. But that doesn’t help you if you run into one of these in the wild (you can’t really ask them, “excuse me, but which taxonomic order are you in?”)

There are a few key ways you can tell these two flat fishes apart. First, look at their tail. Skates typically have shorter, thicker tails than stingrays, and they do not have a stinger. Stingrays get their name from their sharp, stinging barb on their tail that helps them defend themselves. Stings from these venomous barbs can be fatal to humans, so people are encouraged to do the “stingray shuffle” by moving their feet close to the sand when in areas with lots of stingrays. Skates don’t have stingers, so if you spot one, it’s a safe bet it’s a stingray.

Next, look at the fins. Skate’s pelvic fins (the ones closest to their tail) have two lobes where stingrays only have one lobe. If counting pelvic lobes isn’t your thing, skates will often have thorn-like protrusions along their back that help provide protection. Also, stingrays tend to be larger than skates (although this is not a hard-and-fast rule).

The last difference is difficult to spot—skates are oviparous, meaning they lay eggs, where stingrays are viviparous, meaning they give birth to live young. Skates produce egg cases that look like black rectangles with thin extensions on each corner, which are commonly known as mermaid’s purses. If you’ve ever walked along the beach and spotted one of these, congratulations, you saw the home of baby skates!

Although skates and stingrays have their differences, one thing is for sure: these critters are cool. Now you know everything you need to tell these two apart. Now go forth, impress your friends with your Batoidea knowledge!