Question

How many body lobes did trilobites have? A. one C. three B. two D. four

Short answer

Trilobites had three body lobes. Option C is correct.

Step-by-step solution

Understand the Problem

The question asks about the number of body lobes that trilobites had. Trilobites were prehistoric marine arthropods.

Recall Trilobite Anatomy

Trilobites are well-known for their distinct body segmentation. They had three major parts in their bodies:

Identify the Correct Answer

The three major parts of a trilobite's body include a central axial lobe and two pleural lobes, one on each side. Therefore, trilobites had three body lobes in total.

Select the Correct Option

According to the options: A. one, B. two, C. three, D. four, the correct answer that matches the number of body lobes is option C.

Key concepts

Prehistoric Marine Arthropods

Trilobites were fascinating creatures that roamed our planet millions of years ago. They are classified as prehistoric marine arthropods. This means they belonged to a group of invertebrate animals with jointed limbs, a segmented body, and a hard exoskeleton. These creatures thrived in ancient oceans, making them one of the earliest arthropods on Earth. This rich aquatic environment allowed them to develop a diversity of forms and sizes. Trilobites lived during a period known as the Paleozoic Era, with their existence ranging from about 521 to 252 million years ago.

• Extinct species that lived in ancient seas.
• Related to modern arthropods like crabs and lobsters.
• Known for their hard, durable exoskeletons, which fossilized well.

Trilobite Anatomy

The anatomy of trilobites is truly remarkable and distinguishes them from other prehistoric creatures. These ancient arthropods had a unique skeleton structure comprising various distinct components. This was a type of exoskeleton, hard and segmented, providing protection and mobility. Trilobites' bodies were divided into three main sections: the cephalon (head), the thorax (body), and the pygidium (tail).
Each section played a crucial role in their movement and defense strategy. Their anatomy also included facial sutures, compound eyes, and various other anatomical features. Such characteristics helped these organisms survive and adapt in multiple marine environments.

• Three-part body structure: cephalon, thorax, pygidium.
• Possessed compound eyes for enhanced vision.
• Facial features allowed them to molt as they grew.

Body Segmentation

An essential aspect of trilobite biology was their body segmentation. This feature was crucial in their movement and flexibility. The segmented body meant that they could move efficiently through water and even across the sea floor. Segmentation also allowed trilobites to curl up into a ball as a defense mechanism against predators.
This segmented body was subdivided into multiple segments, which were often uniform in appearance but could vary in number among different trilobite species. This adaptive advantage likely played a significant role in their evolutionary success, enabling trilobites to dominate ancient marine ecosystems for a considerable time.

• Body divided into segments for flexibility and protection.
• Ability to curl up for defense.
• Varied appearances due to different species having varied numbers of thoracic segments.

Axial Lobe

Central to the body of a trilobite was a structure known as the axial lobe. This was the main, central lobe running down the middle of their three-lobed body design. It provided the backbone structure, of sorts, for the trilobite, helping it maintain balance and symmetry. The axial lobe was generally elevated above the other parts of the body, providing it with some rigidity and serving as a crucial framework.
The axial lobe is an important distinguishing feature in these ancient creatures, accentuating their trilobed symmetry which is why they're called trilobites. This central lobe was vital, supporting the other body parts and contributing to their robust anatomy.

• Central lobe of trilobite, running lengthwise along the body.
• Provided structural stability.
• Enabled trilobites to maintain their distinct body shape.

Pleural Lobes

Flanking the axial lobe on either side were the pleural lobes. These two side lobes added to the tri-lobed design of trilobites, hence the term 'tri.' The pleural lobes were the areas where the appendages attached, enabling movement and interaction with their environment.
They also played a significant role in the trilobite’s ability to articulate and move. The pleural lobes not only allowed the trilobites to swim or crawl but also provided protection. Each pleural lobe curved outward, terminating in tips that could aid in maintaining stability while moving.

• Flanking lobes, located on either side of the axial lobe.
• Vital for movement and interaction with environment.
• Contributed to the animal’s protective, defensive features through curvature.