Info on the Animal Class Invertebrates
Main Characteristics of Invertebrates:
Invertebrates are animals that don't have a spine. Most animals are invertebrates – only about 4% of all living creatures are vertebrates (mammals, birds, amphibians and reptiles and fish. They also include insects and arachnids, which are being featured in a separate category on animalfunfacts.net. On this page you will find information on molluscs, echinoderms, and crusteans. Invertebrates comprise almost all:
- Molluscs (such as snails, mussels, and squids)
- Echinoderms (such as starfish)
- Crustaceans
- Sponges
- Worms
1. Main Characteristics of Molluscs:
- Molluscs are spineless animals.
- Many molluscs have a shell.
- All molluscs have a radula.
How Do Molluscs Differ from Other Animals?
Unlike other animal species, what nearly all molluscs have in common is the radula. They use it to grate and grind their food. Molluscs do not have a skeleton. Their body mainly consists of soft flesh, which is being held together by muscles and the skin (the so-called “mantle”). Not all of them have a hard cuttlebone, which largely consists of aragonite, like the squids. Not all snails creep around with a shell, there are also slugs that do not have any shell.
Molluks Lifestyle
Where Do Molluscs Live?
Most molluscs live in the water; some are terrestrial animals (snails).
How Do Molluscs Move?
They creep, swim or run.
What Do Molluscs Eat?
Molluscs feed on plant plankton, algae, or lichens. Some of them also eat other molluscs, crabs or fish.
How Do Molluscs Reproduce?
Most molluscs lay eggs. Larvae hatch from the eggs.
Mollusc Fun Facts
Holding a Shell to One’s Ear
If we hold a spiral-shaped conch shell to our ear, we get the impression to hear the sound of the sea. Why? The shape of the shell amplifies every noise near you, no matter how silent it may be. Small and large shells sound differently.
Mollusc Species
There are more than 130,000 species of molluscs:
There is no clear information on how many mollusc species exist. It is a fact that new species are being found practically every day, and there are countless species, which have not been discovered yet. The number of mollusc species can only be roughly estimated.
| Snails: | 100,000 |
| Mussels: | 10,000 |
| Cephalopods/squids: | 1,000 |
| Chitons: | 900 |
Main Characteristics of Echinoderms:
- Echinoderms have a skin with spines.
- Echinoderms always live in the water.
- Echinoderms lay eggs.
Echinoderm Evolution
Echinoderms emerged more than 500 millions of years ago.
Echinoderm Lifestyle
Where Do Echinoderms Live?
They mostly live at the bottom of the sea, primarily in shallow coastal areas.
What Do Echinoderms Eat?
Depending on the species, they feed on plants and/or meat. Sea urchins for example are omnivores or herbivores. Sea cucumbers swallow sand and hope that it contains some nutrients. Starfish hunt for mussels. Sea lilies and feather stars filter the water for food.
How Do Echinoderms Move?
Echinoderms swim, dig, use their little feet, or stay in one place for their entire life.
How Do Echinoderms Reproduce?
Echinoderms lay eggs.
Echinoderm Species
There are about 6,300 species of echinoderms:
| Brittle stars: | 2,000 |
| Starfish: | 1,500 |
| Sea cucumbers: | 1,200 |
| Sea urchins: | 950 |
| Sea lilies: | 620 |
| Feather stars:: | 550 |
3. Main Characteristics of Crustaceans:
- Crustaceans are invertebrates.
- Most crustaceans have a chitinous exoskeleton.
- Crustaceans breathe through gills.
- Crustaceans hatch from eggs.
Crustacean Evolution
Crustaceans have been living on earth for more than 500 millions of years. They are related to insects. Even terrestrial crustaceans breathe through gills.
Crustacean Lifestyle
Where Do Crustaceans Live?
Crustaceans live in all the waters on earth, some are terrestrial animals.
What Do Crustaceans Eat?
Crustaceans feed on plant plankton.
How Do Crustaceans Move?
Crustaceans run or swim.
How Do Crustaceans Reproduce?
Crustaceans hatch from eggs as larvae before developing into fully grown animals.
Crustacean Species
There are about 67,000 species of crustaceans:
| Malacostracae: | 28,000 |
| Mussel shrimps: | 15,000 |
| Copepods | 12,000 |
| Tongue worms: | 130 |
| Fish lice: | 130 |
| Rempipeda: | 24 |
| Horse shoe shrimps: | 11 |
Biodiversity
Who would have thought that sea urchins are important to nature? Fact. Because they eat algae, they prevent them from spreading too much and help to maintain a healthy, healthy underwater landscape. More about biodiversity.
