Invertebrates: Video Scripts
The Brief
TL;DR: I wrote and read variations of these scripts for a series of educational science videos accessible on an online portal (see below).
Target audience: intermediate and advanced English language learners at Spanish junior high and high schools, usually in some sort of bilingual immersion program.
Tone: Casual, informal, like talking to a friend.
Purpose: Inspire curiosity in the animal kingdom and reinforce both science and English language curriculums taught at students’ schools.
Activity: At home or in class, students watched the videos either with or without subtitles, depending on the language level, and then answered questions for vocabulary and comprehension.
SEE WEBSITES:
https://www.themagazine.live/login.php
https://www.planetfraternity.com/
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Intro: Invertebrates. What Are They?
Invertebrates are animals without backbones. That means they don’t have a spine, that series of small bones in your back. Does that sound strange to you? Creatures without backbones? Well, guess what? Most animals on planet Earth are invertebrates. Insects, octopuses, and worms are examples of animals that don’t have backbones.
So vertebrates, which include fish, frogs, lizards, birds, and us humans—are actually outnumbered. If you think about it, then, you have more in common with a turtle or a shark than you do with approximately 95% of all living creatures. So, from now on, when you see a bat or a snake or any other seemingly unusual creature, you might as well view them as a distant relative, because, relatively speaking, they are!
Classification
If there is one thing we like to do in science, it’s classifying things. Can you imagine having to classify every living thing on the planet, from bacteria to blue whales? Just to be clear, we don’t classify animals by size. We have a whole hierarchy of categories and the system of classification has a special name: taxonomy.
It sounds like a clever combination of the words taxes and economy, but taxonomy has nothing to do with either. Language can be misleading!
The word origin is from Greek: taxis means arrangement, and nomia means distribution. Why do we use Greek words for this, you ask? I’ll tell you a little secret. In ancient Greece, Aristotle was one of the first people in the Western world to start classifying things. So you’ll find that many scientific words have Greek (or Latin) origins.
Now let’s look at those categories, from the largest—that doesn’t refer to the size of the organism! It refers to how many animals are in the category—to the smallest. You could also say from the most general, or the broadest, or the most inclusive, to the most specific, the narrowest, or the most exclusive.
Here is the system we use: domain – kingdom – phylum – class – order – family – genus – species. Let me demonstrate how this works by classifying human beings—then we’ll move on to our beloved vertebrates.
There are three domains: Archaea, Eubacteria, and Eukaryota. It’s interesting to note that everything that isn’t bacteria is in Eukaryota (Greek for good + nut, in other words, the whole world in a nutshell!).
You could say all living organisms with more than one cell (and each cell has a nucleus), are part of Eukaryota. The other two domains are basically bacteria and something similar to bacteria: both mainly have one cell.
We’ve gotten carried away. But let’s finish categorizing those categorizing humans, just so you can see how it all works before we move on to all the interesting invertebrates out there. As I was saying, we’re part of the good nutshell domain called Eukaryota. We belong to the kingdom called Animalia, and guess what? That means we’re no longer grouped with plants, but we’re still hanging out with ants…and worms (there are only five kingdoms).
Our phylum is Chordata. Ok, I know I said the next classification after phylum is Class, but animals are so complicated they need a subphylum, and guess what subphylum we belong to? We talked about it in another episode. Vertebrata! Yes. Animals with backbones. The creatures with spines.
Our class is Mammalia. Creatures with four feet and hair. Humans are of the Order known as primates. Getting specific now, right? Primates have more developed brains, and they can grab things with their hands and feet. We’re of the family of Hominidae, hominids not hobbits, like the great apes. Our Genus is the Homo, which in Latin means “man.” And finally, FINALLY, our species is Sapiens, the wise. Yes, we’re the smart ones with spines and all the wisdom, even if we can be quite silly.
Well, that’s our introduction today to one of the most important systems human beings have ever created: the classification of life, the taxonomy of biology. Now let’s explore some invertebrates.
Insects
Insects are the largest group of the Arthropoda phylum. They have three main body parts or segments: a head, a thorax, and an abdomen.
They also have exoskeletons—their bones, or something like bones, is on the outside. They wear their skeleton like a knight wears a suit of armor. Imagine if humans were like that. Ok, don’t. And we’d no longer be human, anyway.
So these exoskeletal insects usually have 6 jointed legs and one pair of antennae. There are so many different kinds of insects—at least a million. More than 90 percent of all organisms on Earth are insects. That’s a lot of insects!
You can find them everywhere. Even though they are cold-blooded, some, like bees, termites, and ants, live in large colonies. So they may be cold-blooded but they can also be very warm social creatures.
And, remember that some bees have the ability to make honey—not bad for a tiny insect with cold blood and a skeleton on the outside of its body.
But these small creatures do something else that has a much bigger impact on our lives than making their delicious honey: along with other members of the insect family, such as butterflies, moths, and flies, bees pollinate the plants we grow for food.
You simply would not have the variety of food available to you if it weren’t for the fact that insects fertilize so many of the crops we depend on, essentially carrying pollen from flower to flower. Of course, birds and bats, and other mammals also do this, but we’re talking about insects here!
So think about that next time you consider stepping on one. They’re our friends…even if they can sting.
Arachnids
Usually, people imagine spiders when they think of arachnids, but scorpions, ticks, and mites also belong to the same class known as Arachnida, which is part of the Chelicerata, a subphylum of Arthropoda.
You may be wondering why a spider isn’t considered an insect. Well, for, starters, spiders, like every other arachnid, only have two main body segments, as opposed to three: the head, which is fused with their thorax into one part, and the abdomen.
Another big difference is that creatures in the arachnid class of the animal kingdom have 8 legs, but neither wings nor antennae. I think that’s enough to put these creatures in a class of their own—so no more calling spiders insects, ok!
And while they do lay eggs like insects, unlike insects, when their babies are born, they are essentially smaller versions of adults.
Here’s an interesting fact: arachnids don’t usually eat solid foods. They have to pour a special digestive juice over their victims before eating them. This juice then transforms everything inside their prey’s body into liquid. Then the arachnid sucks this liquid out. It’s like they turn their prey into bug soup. Yum! I mean yuck.
Mollusks
While the name ‘mollusk’ actually means soft, as most of them are due to their lack of bones, some do have hard shells made of calcium. There are around 85,000 species of mollusks living today. They comprise the second-largest phylum of invertebrate animals in the world and around 23 percent of all marine organisms.
Based on evidence found in fossils, it is believed that many more types of mollusks are out there, we just have yet to learn about them. Octopuses, squids, and cuttlefish stand out as the most famous mollusks, especially because of their highly advanced intelligence. They are testament to the fact that you don’t need bones to have brilliant brians.
I mean, what if I told you that octopuses—not octopi—can have three hearts and, get this, NINE BRAINS! Say that with me: three hearts and nine brains. The central brain, one small brain for each of their eight arms. In other words, their arms have minds of their own, but they are subservient to the big boss. Still. That’s 9 brains. I’d say that’s stranger than anything ever shown in the most bizarre science fiction films, but far more fascinating because these creatures are actually real.
Also, octopuses have mastered the art of camouflage. They have proven their strong short and long-term memory skills, and have even been known to use tools for intelligent purposes, such as building a fortress for protection. But for some reason, they didn’t get “Sapiens” attached to their classification, or some other positive adjective. That’s because humans invented the system of taxonomy so we get to compliment ourselves. I wonder what mollusks call us behind our backs.
Anyways, the giant and colossal squids hold the title of the largest invertebrates in the world, while snails and slugs are the most abundant—about 80 percent— of all mollusks.
In short, if you ever wanted to have a close encounter with an alien intelligence, all you have to do is go spend some time watching certain mollusks.
Crustaceans
A subphylum of Arthropoda, and part of the kingdom Animalia, crustaceans are an indispensable part of the food chain. You can find them in marine, freshwater, and even terrestrial ecosystems. But what are they?
Lobsters, shrimp, prawns, and crayfish are among the 50,000 species of crustaceans that exist. They can be as small as .1 mm and as large as 3.8 meters, like the Japanese spider crab, which weighs around 20kg. The smaller ones eat microscopic organisms, like algae and plankton, while the larger ones have a diet consisting of snails and plants, along with the larvae and eggs of other marine creatures. Some are parasitic, like the fish lice that spend their lives attached to a host.
Since they are arthropods, their skeleton is on the outside; they have an exoskeleton. Yep, another Greek word. Exo, for outside, and skeleton….for skeleton. What sets them apart from other groups of arthropods such as insects, is that they have biramous limbs, two of them to be exact, each of which is parted. Some crustaceans are sessile, such as barnacles, but most are motile, as they can move about freely.
Crustaceans can be either male or female, and reproduce sexually. A small number of them are hermaphrodites; others change their sex during the different stages of their life, and in some species, the female can lay eggs that don’t need to be fertilized by a male. Sorry guys! Don’t need ya!
Crustaceans are a key food source for hundreds of animals, and without them, we’d lose much of the ocean’s biodiversity. Funny how such a small animal can have such a big role to play in the world. Wait till we talk about bacteria one day. But just to give you an example, krill, a very small type of crustacean, is a favorite of our planet’s largest creature, the blue whale, which eats these tiny organisms by the millions as they travel through the sea in immense clouds or swarms.
Imagine that. The largest animal in the world eating one of the smallest in enormous quantities. Like why didn’t they evolve to eat, say, other whales, or seals, or sharks, like Sperm and Killer Whales, do? Why get so big just to eat something so small? Nature works in mysterious ways. But then again, even the largest land animals are vegetarians. Go figure.
Coral
You might not have ever imagined this, but corals are among the most important organisms that we know about on Earth today. They provide the foundations for some of our planet’s most diverse ecosystems, without which many animals of the sea could not exist. Let’s discuss how they do this, and in order to understand how corals do what they do, we have to understand what they are.
Corals are marine invertebrates that belong to the Anthozoa class, of the phylum Cnidaria. They consist of colonies of polyps, and a polyp is one of the two body types you find in the phylum Cnidaria, the other being the medusa. Polyps are cylindrical sessile creatures, and they often look like little trees, with their trunk-like structure which opens up into a set of branches, or better yet, tentacles, with which they snatch food in the water.
Typically, you find these little polyps living in colonies, where each individual polyp is identical to the next. To protect themselves, polyp colonies construct hard structures made up of minerals, which shelter them from any predators.
Think of corals as both the colonies of polyps and the houses in which they live. What’s fascinating is that over millions of years, these hard mineral houses get larger and larger, becoming immense superstructures that provide homes to not only the polyps but to many other creatures. These superstructures are called coral reefs, and they lay the foundation for large food chains.
In fact, the largest coral reef is off the coast of Australia, and it’s 2,600 km long. It’s so large you can even see it from outer space! Coral reefs are vital for the livelihood of all types of fish, sharks, eels, jellyfish, sea stars, crabs, shrimp, lobsters, turtles, sea snakes, octopuses, clams—even birds—and much more. If corals were to die, then so would many of the animals that depend on them. Humans would be left with an ocean empty of food, and without beauty.