Back to: SCHS|PCA 2025/26 – Science: Biology (8/9)
Invertebrates are the second major grouping of aquatic creatures.
These are all the creatures who have no internal skeleton or central spine.
- There are flying invertebrates (like butterflies) , land invertebrates (like spiders) and aquatic invertebrates (like squid).
- If we had one of every species of animal, 90% of them would be invertebrates…over 1 million different species. If we count every single living animal, 99.99% of them are insects.
INvertebrates
- Mollusk (soft body)
- Arthropod (joint foot)
- Protozoa
- Worms
- Cnidarian (stinging)
- Porifera (with pores)
- Echinoderm (prickly skin)
- Extinct Aquatics
Mollusks
- Mollusk means soft body and is named after a soft nut, because they’re both soft inside.
- The three types of mollusks are the belly foots, the head foots and the double-doors.
Man Behind the Mollusk
Georges Cuvier was the man who gave us the name mollusk. Cuvier (pronounced COO-vee-eh) was a founder of paleontology and comparative anatomy. He firmly believed the earth geology was shaped by a series of catastrophes, the last of which was the global flood.
Cuvier was a good friend of Linnaeus and was a firm creationist, participating in debates against evolution.
Gastropods (belly foots)
Named because their belly sits on top of their single foot. Snails are the perfect example.
Cephalopods (head foots)
Named because their head and their feet look like a single unit. Octopuses and squid are the two most common.
- Squid. Squid have a single bone in their body called a pen. Most squid are about one foot long with eight arms. They have two long tentacles to grab fish with and eat with their sharp beak. Squid produce their own bioluminescent light.
- Giant Squid. The giant squid is a favorite food of Sperm Whales.
- Octopus. Let’s get it straight. Octopus is singular, “one octopus.” Then, depending on the dictionary you use, there are three possible plural forms.
- Everyone agrees that octopuses is correct, as in “here are three octopuses.”
- Octopods or octopodes is also acceptable especially in academic circles.
- Then there is the controversial octopi. Many dictionaries list this as acceptable but recognize that it is technically incorrect because octopus is Greek and not Latin. Stick with octopuses (and hippopotamuses for that matter) and you won’t go wrong.
- Octopuses are beyond weird. Their body is like a sloppy, half-filled rubbery bag which can rapidly change colors at will. They have eight arms that come out of that bag and a double row of suckers down each arm used to grasp and taste things. They can shoot out a stream of inky black fluid as a smoke screen and their mouth looks like a large version of a parrot’s beak. Plus, for an animal, they display an intelligence that considers options, plans and can strategize.
- The Nautilus. (The plural is nautiloids) You almost never see a live nautilus but you almost always see their empty, mathematically symmetrical shell. Each empty chamber can be filled with gas allowing vertical movement through the water.
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Fighting Cephalods
When two octopuses fight, their colors change rapidly, flashing from one color to the next: green to purple to white and back again. Octopuses make their house by propping up a large flat rock with several supporting rocks under it. Divers have seen entire octopus cities off the shallows of the Mediterranean Sea.
Bivalves (double doors)
Most people assume that the term bivalve refers to how these creatures pull water in through one siphon and squirt the water out of another siphon.
Actually, the term valve means “a door”; something that opens and closes.
Water valves were named after this door-idea of opening and shutting, allowing things in and out. Bivalves were so named because of their two shells with a hinge in the middle.
Clams and Oysters. These are often called shellfish. As mentioned above, they eat by siphoning water and food particles in and out of their shells. Oysters often get a piece of sand caught inside and the secretion they produce to isolate the irritant eventually builds up until a valuable pearl is formed. Thus, inside every valuable pearl, is a common grain of sand.
Pigs or Pears
Pearl is Latin and means ham. A pearl comes from an oyster shell which is roughly shaped like a ham. Another theory says it means pear, also based on the shape of the shell.
Aquatic Arthropods
- Arthropod means jointed foot and there are thousands of different kinds of creatures with this design feature: land, air and aquatic arthropods.
- The aquatic arthropods are commonly called crustaceans which literally means, with a crust.
- Lobsters, crabs and crayfish are common crustaceans. They have three distinct body sections; head, thorax (chest) and abdomen (belly). Their shells are made of chitin (pronounced KITE-n) which doesn’t stretch. This is why these creatures shed, or molt their exterior shell from time to time when they outgrow the old shell.
- Barnacles are another crustacean. The actual creature lives inside the hard, cone shaped shell. When the tide comes in, a little wand-like appendage with a rake on the end waves through the water collecting bits of food. Barnacle glue is some of the strongest in the world.
protozoa
- Protozoa are microscopic, unimaginably complex one-celled mini-beasts.
- The word protozoa means first animal which reflects an evolutionary philosophy and not a scientific observation. Small animals would probably be more accurate.
- Most protozoa reproduce by dividing directly in half, a process that takes about 20 minutes.
- Although there are over 30,000 identified protozoa, the three most well known members are: euglena, amoeba and paramecium.
Euglena (good eye)
An aquatic animal that moves around with a little whipping tail called a flagellum. They actually use photosynthesis to make food, just like plants. Plus they can eat microscopic bits of food if they need to. They have an eye spot that directs them to sunlight to aid in photosynthesizing their food.
Amoeba (to change)
The amoeba looks like a slowly moving blob. They’re known for their pseudopods or fake feet which slowly reach out and envelop a food bit. The surrounded area is called a vacuole (meaning empty). Enzymes break the food down so the amoeba can ingest it.
Paramecium (oval)
Paramecias move rapidly around using wavy hairs called cilia. For their size, their speed is the equivalent of a man running about 70 mph.31 Paramecium have a mouth (the oral groove), a nucleus that directs basic activities (sort of like a basic brain…but not really), vacuoles to sponge up excess water and weapons that shoot out from the edges to attack or defend.
worms
Worms come in several varieties. Flatworms, roundworms and segmented worms. Most parasites that are small enough, will embed themselves in body tissue. This helps them hide from the immunity system. Icky.
Flatworms
Flatworms include flukes and tapeworms. They are usually ingested by eating improperly cooked meat. They cause internal problems in animals and people.
Roundworms
Roundworms are also known as nematodes meaning thread worm…round like an earthworm but no segments…just like a thread. Most roundworms are terrestrial but for convenience they are here with the other worms.
Pinworms are among the most prevalent parasitic problem in American children but medicine can cure the problem. Hookworms are a disgusting worm that lives in unsanitary conditions. They pierce into bare feet, then burrow inside and–you can look up the rest on your own.
Segmented worms (leeches)
Leeches are in the same phylum as earthworms, Annelida, meaning ringed, and are considered a flat worm. Leeches live in water or very wet earth and attach to the outside of their host where they eat blood. They are such tenacious parasites that the word leech, has come to mean ‘someone who clings to another in order to get what he can from him’.
The family name Leach is an occupational name meaning physician. It comes from the practice of using medicinal leeches to help eliminate impurities from a sick person.
Leech Therapy
Leech therapy involves applying leeches to a wound to increase circulation, improve blood flow, and promote healing. Its practice has varied over time, but it continues to be used in modern surgery, mostly used in plastic and reconstructive surgery. This is because leeches secrete peptides and proteins that work to prevent blood clots. These secretions are also known as anticoagulants. This keeps blood flowing to wounds to help them heal.
How Does It Work?
Medicinal leeches have three jaws with tiny rows of teeth. They pierce a person’s skin with their teeth and insert anticoagulants through their saliva. The leeches are then allowed to extract blood for up to 45 minutes at a time from the person undergoing treatment. This equates to a relatively small amount of blood, up to 15 milliliters per leech. People who may benefit include…
- those who risk limb amputation due to the side effects of diabetes,
- those who have been diagnosed with heart disease
- those who are undergoing cosmetic surgery in which they risk the loss of some of their soft tissue.
- It has also been recommended to treat blood clots and varicose veins.
People with anemia, blood clotting conditions, or compromised arteries are not candidates for leech therapy.
Children under the age of 18 years old and people who are pregnant are also usually advised to avoid it.
Parasites are organisms that live on or in another animal or plant, obtaining their sustenance from that host. Parasites are corruptions of creatures that were originally part of God’s “very good” creation. Exactly what they were before the fall or if they were aquatic or land creatures is anybody’s guess. We have classified them as being primarily 5th day aquatic creatures.
cnidarian (Stinging)
Cnidarians are a group of sea creatures with stinging tentacles. They include seajellies, the Portuguese man-of-war, sea wasp, sea anemones and coral. The word is pronounced nye-DARE-ee-uns.
Jellyfish (seajellies)
Jellyfish are not, of course, fish. They are more properly called seajellies and there are over 200 different kinds of seajellies. They swim by contracting their bells allowing their long stinging tentacles to gracefully follow behind them. The stinging cells are actually spring-loaded and can fire even if the seajelly (jellyfish) is dead.
Portuguese Man-of-War
The man-of-war is a colony of four creatures that work together to make this one creature. They are completely at the mercy of the wind and travel in groups of 1000 or more. Their sting is painful but rarely fatal. The Portuguese man-of-war got its name from medieval sailors who compared it to a Portuguese sailing ship. (Read or listen below to AIG)
The man-of-war is also called the bluebottle due to it’s transparent blue color. Once the man-of-war is beached on the sand, the animals that made up the colony die. The tentacles can still fire for some time after the animal dies. The man-of-war is a favorite food of sea turtles.
Sea Wasp
This is possibly the most venomous creature in the Indian Ocean and surrounding seas. The sting from the sea wasp causes respiratory paralysis and death within 2-3 minutes.
EAT OR INJECT – Poison is something you eat or absorb in your skin. Venom is injected into your skin through fangs, stinging cells or stinging spines.
Sea Anenomes
Sea anemones are found in a wide variety of shapes and colors but all are stationary stinging creatures that eat smaller creatures. They are sometimes called an upside down jellyfish and their class name (anthozoan) means “flower animal.” Some crabs will actually pick up anemones and use them as weapons against attacking animals.
Coral
We generally don’t think of coral as stinging creatures, in fact we hardly think of them as creatures at all. Coral reefs, made up of thousands and millions of little stinging creatures hidden inside these hard limestone tubes, are what we usually see and think of when it comes to coral.
Stung by a Cnidarian?
- Never rub the affected area.
- Use a credit card or driver’s license to scrape off the tentacles, which are almost invisible.
- Rinse off with vinegar (or even saltwater)to stop the cells from firing.
- Do not use fresh water which can cause more venom to be released.
- Applying alcohol, meat tenderizer, ammonia or baking soda are common solutions to ease the pain but results are mixed and still under study.
- If itching or allergic reaction occur, many doctors recommend keeping an antihistamine like Benadryl® handy. Get to a physician as soon as possible.
Remember: The tentacles can continue to sting for some time even after the animal is dead and drying or if the tentacles are broken off.
Porifera
- Sponges are such unusual animals they get their very own phylum, Porifera.
- There are nearly 6,000 different kinds of sponges but only six are sold as bath sponges.
- Once the sponge dies, it leaves a skeleton made of tough fiber. This is the part we know and use as natural sponges.
- Sponge ‘farmers’ divide living sponges in pieces and attach the pieces to cement blocks which act as an anchor. The blocks are thrown back into the sea and in about four years, the pieces will have grown into larger sponges again.
Sponges pump water in and out to filter food. They are so efficient at pumping that a sponge the size of a one gallon milk jug, can pump enough water everyday to fill a residential swimming pool.
BArely an Animal
A sponge appears to be the only multicelled animal that does not have any kind of a nervous system or brain. If you touch a sponge, only those cells you actually touch will respond. The rest of the animal seems completely unaware of what’s happening.
In fact, a sponge has no heart, stomach or muscles either.
It’s classified as an animal only because it sort of captures its food and has no photosynthesis. Sponge cells more resemble a collection of protozoa-single-celled animals!
Original Cancer Drug
One of the first drugs for treating cancer, and still widely in use today, is cytosine arabinoside. It was isolated from sponges.
Echinoderms
There are three important animals in the echinoderm phylum: Starfish, Sand Dollars and Sea Urchins. All have a rough bumpy skin which is why they’re in the prickly skin category.
Seastars (starfish)
Starfish are not fish and are more properly called “seastars.” Seastars are in the class Asteroidea which means star shaped. They are carnivorous predators and fairly voracious eaters, consuming a dozen or more clams and oysters daily. Clam and oyster fishermen aren’t particularly fond of seastars. They straddle the clam (the seastar, not the fishermen) and using their powerful suction tube arms, they pry the clam apart. The seastar’s stomach attaches to the clam and digests it, right there inside the clam’s own shell.
Sand Dollars
Sand dollars like to live in the sand and in shallow water. This is why they are so common on the shore. A living sand dollar looks a lot like their skeleton but covered with little spines. They move about using these spines and gripping tube feet.
Sea Urchins
Sea urchins are like sand dollars except they have much a rounder body and longer spines…like a spiky tennis ball. They move around scraping algae off rocks and looking for an occasional slow moving morsel. The scraping jaws of a sea urchin look a little like a lantern, according to the Greek philosopher Aristotle who studied them. They have been called Aristotle’s Lantern ever since.
Extinct Aquatics
There is evidence that many different marine creatures once existed that are no longer on earth. The Flood wiped out a huge number of aquatic creatures as evidenced by the millions and millions of aquatic fossils found all over the world that were suddenly buried in tons of silt and water. These aquatic creatures include Trilobites, Elasmosaurus, Ichthyosaurus, Dinichthys, Orthacanthus, the Megaladon, Plesiosaurus, Kronosaurus and Leviathan.
- Some creatures, like the Coelacanth (SEE-luh-kanth), were thought to be extinct. However, in 1938, a woman found one in a Madagascar fish market and showed it to scientists. Many have been found since then.
- The Okapi is a land animal also thought to be extinct. They too, were found alive deep in the Congo River basin in 1901.
The Ocean is Large
No doubt there are many other marine animals hiding somewhere in the ocean depths. The world’s oceans cover more than 2/3 of the entire planet. At the deepest known point, Mount Everest would be completely submerged with a mile of water still on top.
The well known marine biologist Dr. Clyde Roper said scientists have been scanning the ocean for over 50 years and in all that time, they’ve observed less than 50 square miles of the entire ocean floor …and the oceans cover 140 million square miles.
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