Chapter 27, Problem 3STP

Summary Introduction

Introduction:

Most of the animals are invertebrates. They do not possess a vertebral column. Invertebrates do not have a backbone. They vary in size from tiny mites to almost unseen flies to giant soccer-scale eyes to squids. This is by far the biggest group in the animal kingdom. Invertebrates constitute 97% of all species.

Answer to Problem 3STP

Correct answer:

The correct answer is option (B) Flatworms have flame cells.

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) Flatworms have flame cells. A flame cell is a specialized cell present in the simplest invertebrates, including flatworms, rotiers, and nemerteans. These are the mammals with the most basic organisms with a specific excretory mechanism. So, this is the correct answer.

Explanation for incorrect answer:

Option (A) Cnidarians have collar cells. Cnidarians used stinging cells or nematocysts to eject venom from snakes. They do not have collar cells. So, this is an incorrect option.

Option (C) Flatworms have nematocysts. Flatworms have flame cells. Cnidarians have nematocyst. This is not a correct statement for a group of invertebrates. So, this is an incorrect option.

Option (D) Sponges have a nervous system. Sponges do not have a nervous system. They lack even neurons, tissues, and brains. This is not a correct statement for a group of invertebrates. So, this is an incorrect answer.