Problem 17 - Biology

Question

Crustaceans are _____________. a. ecdysozoans b. nematodes c. arachnids d. parazoans

Step-by-Step Solution

Answer

a. ecdysozoans

Step 1: Understand the Terminology

First, it's important to understand the definitions of the options given. Ecdysozoans are animals that grow by molting their exoskeleton. Nematodes, also known as roundworms, are a type of worm. Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. Parazoans include organisms that are thought to have only a simple level of tissue organization, like sponges.

Step 2: Identify Characteristics of Crustaceans

Crustaceans belong to the phylum Arthropoda and have a hard exoskeleton, which they molt in order to grow. This molting process is a characteristic feature of ecdysozoans.

Step 3: Match Crustaceans with the Correct Option

Knowing that crustaceans molt their exoskeletons, the correct classification is ecdysozoans. They are not nematodes, arachnids, or parazoans.

Key Concepts

Ecdysozoans

Ecdysozoans are fascinating creatures characterized by their unique growth process. They undergo molting, a developmental phenomenon. Molting allows them to shed their old exoskeleton and grow a new one. This process is crucial because their exoskeletons, while providing protection, do not grow as they do. Ecdysozoans include several major groups such as arthropods and nematodes. By molting, or ecdysis, these animals can continue increasing in size throughout their lives.

Arthropoda

Arthropoda is the largest phylum in the animal kingdom, comprising an astonishing variety of creatures including insects, arachnids, myriapods, and crustaceans. These animals are characterized by their exoskeleton, segmented bodies, and jointed limbs. The exoskeleton provides both support and protection, but one of its unique features is its role in the molting process.
Arthropods can be found in almost every habitat on Earth, ranging from deep ocean floors to the highest mountains. Their adaptability and diverse range of physical and behavioral traits make arthropods a vital part of Earth's ecosystems.

Exoskeleton Molting

Exoskeleton molting, also known as ecdysis, is a fascinating and necessary process for ecdysozoans. This process allows arthropods to grow despite having a rigid outer shell. Here are the steps involved in molting:

• The animal secretes enzymes to separate the old exoskeleton from the underlying skin.
• A new exoskeleton forms beneath the old one.
• The old exoskeleton splits, and the animal typically wiggles out of it. This step can leave the animal temporarily vulnerable to predators.
• The new exoskeleton hardens and darkens, providing renewed protection.

This critical process ensures that arthropods can grow and adapt to their environments throughout their lives.