Whales, sharks, squids, dolphins – the ocean is full of amazing creatures, but do you know what differentiates them all? With so many amazing animals beneath the sea, it can be hard to know what’s what.
To help you get to grips with the wonderful creatures which inhabit our seas, rivers, lakes and coasts, we’re here with a helpful guide on how to tell them all apart. From mammals to molluscs, fish to reptiles, you’ll soon have a much better understanding of what makes our natural world so unique and so diverse.
And to make sure you absorb all that, we’ve put together a challenging animal classification quiz, which asks you to decide into which category a handful of amazing animals fall; be sure to give it a go to put your knowledge to the test.
What Are Mammals?
Mammals are vertebrate animals, meaning they have a spinal cord surrounded by cartilage or bone. They’re characterised by having mammary glands, which produce milk for their young, as well as fur or hair, and a neocortex in their brain; this controls things like spatial awareness, reasoning and the perception of senses.
Mammals are divided into three subclasses based on how they reproduce and give birth to their young. These are placentals, marsupials and monotremes. If you’re wondering which of these us humans fall into, it’s placentals.
What Differentiates Mammals from Other Animals?
There are five things which differentiate mammals from other animals, like fish and amphibians. These are:
- Presence of hair or fur
- Warm blood
- Mammary glands
- A complex brain, with a neocortex
- Produce live young (except for monotremes, which lay eggs)
What Are Fish?
Fish are marine animals that live in water and don’t breathe air. Instead, they have gills which are used to extract oxygen from water – meaning they rely on a constant supply of water to survive.
There are hundreds of different fish living in our oceans, rivers and lakes, and biologists continue to uncover new species. When they reproduce, they lay lots of small, soft eggs, but only a few of these will survive to adulthood. Fish come in all sorts of different sizes, ranging from the biggest, the whale shark, to the smallest, the dwarf minnow, which are only a few millimetres long.
What Differentiates Fish from Other Animals?
There are a handful of differences between fish and other animals you need to be aware of, including:
- All fish are cold-blooded, or ‘ectothermic’. This means they rely on external sources to regulate their body heat. That’s why some species stick to warm waters, while others have adapted to survive in cold climates
- All fish live in water, and rely on it for their survival. They’re the only animal on Earth that is confined to one singular habitat type
- Fish use gills to breathe, extracting oxygen from water
- Fish have no limbs, instead relying on their fins and muscles to move through the water
What Are Crustaceans?
Crustaceans are animals which belong to the invertebrate family, meaning they have no spinal column. All of these unusual animals have a shell and move around on jointed legs, while many also have pincers, which they use to grip things and as a form of defence. Most live in the water, including crabs, prawns, shrimps and lobsters, while some, like woodlice, live on land.
Like fish and mammals, crustaceans come in a vast variety of different shapes, sizes and colours. The smallest crustacean on Earth is believed to the pea crab (about the size of – you guessed it – a pea), while the largest is the Japanese spider crab, which can grow up to 4 metres in diameter – yikes!
What Differentiates Crustaceans from Other Animals?
To help you understand the difference between crustaceans and other animals, here are some of the important features to note:
- Crustaceans have an exoskeleton (their shell) which ‘moults’ as they grow
- All crustaceans also have ‘biramous’ limbs, meaning two-parted. This differentiates them from insects and myriapods
- Crustaceans breathe in different ways depending on their size. Larger species have gills like fish, while smaller crustaceans breathe through their bodies
- Crustaceans live in water and on land
What Are Molluscs?
Molluscs are invertebrate animals that have soft, unsegmented bodies. They usually live in damp or underwater environments, and include species like snails, slugs, mussels, octopuses and squids.
Lots of molluscs are wholly or partly contained within a shell, which is designed to protect them from predators. Marine molluscs, those that live in the sea, breathe through gills, while those on land exchange gas with air through something called the ‘mantle cavity’.
What Differentiates Molluscs from Other Animals?
If you want to learn the difference between molluscs and other animals, here are some of the things you need to know:
- Molluscs are invertebrates, meaning they don’t have a spine. Their bodies are soft, and aren’t segmented like those of annelids, like worms
- Lots of people get crustaceans and molluscs mixed up because of their shells. Some molluscs grow shells as a means of defence, while others don’t
- Molluscs can live in water and on land. This is what differentiates how they breathe
What Are Reptiles?
Reptiles are air-breathing vertebrate animals that include species like crocodiles, snakes, lizards and tortoises. They can live on or at sea, but unlike fish, they need to come up for air – just like mammals.
Like fish, reptiles are cold-blooded creatures, so they need to find ways to regulate their body temperature. One of the ways they do this is through their tough skin, which is made up of scales and bony plates, perfect for insulation and defence. Most reptiles have a slow metabolism, meaning they don’t grow very fast, and so can live to some impressive ages.
What Differentiates Reptiles from Other Animals?
Generally speaking, reptiles sit between mammals and fish from an evolutionary standpoint, and share similarities with both. Here are some of the things to remember about these curious creatures:
- Reptiles are cold blooded, like fish. That’s why you’ll often find lizards lazing in the sun, warming themselves up
- Some reptiles lay eggs, and they’ll often incubate them like birds. However, some give birth to live young, like mammals
- Reptiles breathe oxygen through the lungs, just like mammals. However, they can swim underwater for an impressively long time
- Reptiles have scaly skin
What Are Amphibians?
Amphibians are small invertebrate animals that rely on a wet or moist environment to survive. That’s because they absorb oxygen from water through glands in their skin.
There are many different types of amphibians, including frogs, toads, newts and salamanders. Some of them may look like reptiles, but they’re very different, and amphibians must always be in a moist environment for their survival.
What Differentiates Amphibians from Other Animals?
Often get amphibians and reptiles mixed up? Here are some of the things you need to remember when deciding if something is an amphibian or not.
- Amphibians will always be found near water, and rely on it for absorbing oxygen through glands in their skin
- Amphibians, like fish and reptiles, are cold-blooded, so they rely on external sources to regulate their body temperature
- They have scale-less skin, unlike fish and reptiles
- One of the biggest dangers amphibians face is dehydration
- Some amphibians can change colour when they feel threatened; this is used as a defence mechanism
Take Our Creatures Classification Quiz!
Now that you know the difference between mammals, fish, crustaceans, molluscs, reptiles and amphibians, it’s time to put your new-found knowledge to the test by taking our creatures classification quiz.
All you have to do is match the animal with the correct classification category. Sound simple? Give our quiz a try below.
How did you get on? Do you really know your molluscs from your mammals? Or are you left scratching your head? We’d love to hear how you did, so get in touch with your score on the Bristol Aquarium Facebook page.
Looking to learn more about the creatures of the deep and what sets them apart? Join us for a memorable day out at Bristol Aquarium, where our knowledgeable experts can help bring you closer to the wonders of the deep. For more information, visit the homepage today.