Question

Metameric segmentation is found in (a) Annelida (b) Arthropod (c) Both (a) and (b) (d) Platyhelminthes

Short answer

The correct answer is (c) Both (a) and (b). Both Annelida and Arthropod exhibit metameric segmentation.

Step-by-step solution

Understanding Metameric segmentation

Metameric segmentation is a type of body organization where the body is divided into segments, each of which is a repetition of compartments that contain a complete set of organs. Metameres, the units of body segmentation play an essential role in the development and survival of organisms as they allow duplicity of organs and recovery from damage.

Assigning Metameric Segmentation

Research shows that metameric segmentation is clearly present in Annelida and Arthropoda. Annelids or segmented worms are characterized by both external and internal segmentation, while arthropods - which include insects, spiders, and crustaceans - display external segmentation.

Negating Metameric Segmentation

Platyhelminthes do not exhibit metameric segmentation. This group, also known as flatworms includes some of the simplest organisms at the tissue level of organization.

Key concepts

Annelida

One of the most fascinating aspects of the Annelida, or segmented worms, is their distinctive body structure, showcasing what is known as metameric segmentation. This biological concept implies that their bodies are divided into multiple segments or metameres, each resembling the others to a certain degree.

Each segment of an annelid's body includes its own set of organs and muscles, which allows for complex movement and flexibility. Internally, structures such as nerves and blood vessels are also repeated in each segment. This feature enables Annelids to survive injury or loss of a segment because the remaining segments can often compensate.

Examples of Annelida

Consider earthworms, which are one of the most recognizable members of this phylum. Their body consists of a series of ring-like segments, which is easily observable to the naked eye, providing them with the ability to move efficiently through soil. Leeches are yet another example, leveraging their segmentation for efficient locomotion in aquatic environments.

Arthropoda

When it comes to Arthropoda, the largest phylum in the animal kingdom which includes insects, arachnids, and crustaceans, metameric segmentation forms the backbone of their structure as well, but with a unique twist compared to Annelids.

While Annelids have both internal and external segmentation, Arthropods typically demonstrate their segmentation externally. Their body is separated into distinct regions such as the head, thorax, and abdomen, each containing repeated segments. The external skeleton, or exoskeleton, is a chitinous armor that segments into plates to allow for movement.

Jointed Appendages

Characterizing this phylum are jointed appendages — legs, antennae, and other body parts — which have enabled them to occupy a variety of ecological niches, from the deepest ocean trenches to the skies above. The segmentation in Arthropoda has enabled these creatures to evolve specialized segments and appendages adapted to their diverse lifestyles.

Biological Segmentation

Biological segmentation, also known as metamerism, is a structural characteristic where an organism's body is serially divided into segments. This evolutionary trait allows for redundancy in organ systems and improves the organism's locomotive capabilities.

Beyond Annelida and Arthropoda, segmentation can be seen in other animals, yet it is not as complex or is absent, as in the unsegmented Platyhelminthes. Metameric segmentation may vary from having a superficial appearance to involving profound divisions of internal body structures.

Importance in Evolution

This adaptable body plan has had immense evolutionary significance, enabling segmented animals to thrive in various environments. It provides not only a blueprint for growth and development but also for diversification and specialization among species.

NEET Biology

For students preparing for competitive exams like the National Eligibility cum Entrance Test (NEET) in India, understanding concepts such as metameric segmentation is vital. NEET Biology covers a vast array of topics within Zoology and Botany, encompassing the intricacies of animal anatomy and physiology.

Candidates are expected to have a thorough grasp of the principles behind biological segmentation as it often forms the basis for broader questions related to evolutionary biology, adaptation, and biodiversity. Clear insights into how organisms like Annelids and Arthropods exhibit metameric segmentation could be instrumental in securing the knowledge essential for tackling questions in the NEET examination.