Meet A Shark’s Closest Relative: The Stingray

By: Jenna L. Eckel

Certainly, some of your fondest family memories are times with your cousins. From family vacations to holiday seasons you may even consider your cousins some of your closest (and maybe favorite) relatives. While humans use historic records to track their family tree, the animal kingdom too has a web of family members, including sharks and stingrays. Surely, these are two animals that might have a different cousin relationship than what you’re familiar with, but like you and your closest cousin they still have a lot in common.

Shark

1). They have a big family

There are hundreds of shark and stingray species in the world. In fact, there are 400 known species of sharks and more than 500 ray species. At Adventure Aquarium, you’ll meet 12 species of sharks, including a great hammerhead, black tip reef and sand tiger sharks, featured in Ocean Realm and Shark Realm and eight species of rays including cownose, leopard, Atlantic, rough tail and southern stingrays.

Sharks

2). They’re threatened

Unfortunately, several species of sharks and rays are considered critically endangered, threatened or vulnerable according to the IUCN, and are protected under the U.S. Endangered Species Act. As an AZA member, Adventure Aquarium participates in development, research and conservation programs including AZA SAFE, a program that focuses on saving animals from extinction. In fact, Adventure Aquarium created the Action for Animals audio tour to teach guests about different conservation efforts that Adventure Aquarium takes part in and things you can do at home!

Shark

3). They’re made of cartilage!

Sharks and rays are part of the Chondrichthyes taxonomic classification (try saying that three times fast!). That is a big fancy term just meaning “made of cartilage” – the same material your nose and ears are made of. Instead of bone, their skeletons are cartilaginous.

Stingrays

4). They look alike… (Really?)

Seriously, hear us out on this one – Sharks and rays both have flat bodies (some sharks are flatter than others, like a nurse shark) their mouths are on the undersides of their bodies and they have long slender tails.

Also, if you have the chance to (safely) get up close to these animals, like at Stingray Beach Club and Touch a Shark, you’ll see they both have “dermal denticles” which translates to “skin teeth. They are also known as placoid scales. This type of scale is found in all Chondrichthyes and is made of the same material as your teeth! These scales are sort of like body armor that grows as part of a sharks or rays’ skin. Interestingly, scales do not get bigger as a shark or ray grows up, they just grow more scales.

You’ll see when you visit the Aquarium that they feel like sandpaper.

Stingrays

5). Their livers control their buoyancy

Sharks and rays typically have oversized or large livers compared to other animals of similar size. The oil in their livers can help them control their buoyancy.

Some sharks like our sand tiger sharks can occasionally seen gulping for air at the surface. They swallow this air to help them become more positively buoyant and they "belch" it out to become more negatively buoyant.

Shark

6). They don’t have lungs

All Chondrichthyes breathe using gills instead of lungs.They breathe by moving water across their gills. The gill filaments remove oxygen from the water and into their blood. The gills also release Carbon Dioxide as waste into the water completing the cycle.

Some sharks have to continually move in order to force water across their gills, this is called “Ram Ventilation.” Other sharks and rays can pump water across their gills allowing them to rest or hide on the bottom, this is called “Active Ventilation.”

The holes on the top of a stingray (typically just behind the eyes) are called spiracles. "Spiracles" help the stingray move water across their gills and out the top of their body so that they can hide entirely under the sand.

Shark

7). They have big hearts…

…well, sort of. Chondrichthyes are known for having two heart chambers. One chamber pumps the blood into the heart, while the other chamber pumps the blood back out of the heart. A two-chambered heart is a common characteristic in animals who use gills to breathe.

Stingrays

8). They swim in the same circles

Sharks and rays come from worldly families. They can be found in fresh and salt waters, tropical, subtropical, temperate and cold environments, shallow or deep conditions and open or coastal ecosystems.