【PEP】Junior High Biology Grade 8 Volume 1: Into the Animal World — The Secrets of Classification and the Boundaries of the Spine

Embark on a Journey into Biodiversity

Earth is home to a vast array of animal species, with approximately 1.5 million known to date. To make sense of this immense diversity of life, scientists use the method ofclassifying organisms based on their characteristics. In this grand experiment of classification, the most critical dividing line is whether an organism possesses a rigid central axis inside its body — thespine.

Definition of Vertebrates

All animals that have a spine composed ofvertebraeare collectively calledvertebrates. They include fish,amphibian,reptiles, birds, and mammals. The spine not only supports the body but also protects the vital nerve pathway inside — the spinal cord — serving as the physical foundation for life to evolve toward higher complexity.

Invertebrates: The Silent Majority

In contrast, animals without a spine made of vertebrae are called invertebrates. From the structurally simpleplanariansto mollusks with a well-developedmantle, to arthropods covered with anexoskeleton withsegmented bodies and appendages, they showcase the boundless possibilities of life without the support of an internal skeleton.

Evolution Quick Tip

The emergence of the spine was key to the transition of life from water to land. Working with powerful muscles, it enables animals to overcome gravity — running, jumping, and soaring across the land.

QUESTION 1

Determine whether the following statement is true or false: All mollusks have shells.

✓ True

✗ False

QUESTION 2

Based on what you've learned, determine whether the following statement about animal classification is correct: Any animal that does not have a spine made of vertebrae is an invertebrate.

✓ True

✗ False

QUESTION 3

Which group of animals below all have the character for "fish" in their Chinese names, but none of them are actually fish?

Ribbon fish, Cuttlefish

Octopus, Squid, Cuttlefish

Crucian carp, Whale

Abalone, Crocodile

QUESTION 4

Match Pairs: Connect each animal group with its correct characteristic.

Cnidarians — Have stinging cells on body surface; Flatworms — Flat body, mouth but no anus; Mollusks — Body has a mantle; Arthropods — Segmented body and limbs, with an exoskeleton

QUESTION 5

True or False: Vertebrates have well-developed muscles attached to both sides of the body, and this is unrelated to their movement function.

✓ True

✗ False