Question

Metamerism is found in (a) Ascaris (b) Leech (c) Loligo (d) Octopus

Short answer

The organism among the listed that exhibits metamerism is (b) Leech.

Step-by-step solution

Understanding Metamerism

The first step is to understand the concept of metamerism. Metamerism is a form of symmetry in which an organism's body is divided into a series of similar segments, such as segments in earthworms or leeches.

Applying Knowledge on Organisms

The next step is to apply our knowledge of these organisms. Ascaris and Loligo are roundworm and squid respectively, and they do not exhibit metamerism. Octopus, despite being a cephalopod like the Loligo, does not have segmental body plan either.

Determine the Correct Answer

The last step is to determine the correct answer. Among the listed options, leeches, also known as hirudinea, exhibit clear segmentation of the body, thus showing metamerism. So, the correct answer is (b) Leech.

Key concepts

Biological Symmetry

Biological symmetry refers to the balanced distribution of duplicate body parts or shapes within the body of an organism. In nature, we commonly encounter two main types of symmetry: radial and bilateral. Radial symmetry, found in organisms such as jellyfish and sea anemones, is characterized by body parts arranged around a central axis. On the other hand, bilateral symmetry, seen in humans and many animals, has body structures that are mirror images along a midline called the sagittal plane.

When studying biological symmetry, it's crucial to understand that it not only affects an organism's appearance but also has implications for their lifestyle and evolution. Bilateral symmetry, for instance, is often associated with a more active lifestyle and the development of a head region (cephalization) which houses sensory organs and a brain. This symmetry helps with directional movement and streamlining which is vital for predators or animals that move constantly in search of food.

Segmentation in Organisms

Segmentation is a fascinating topic in biology that refers to the division of an organism's body into repeating units called segments. This concept is crucial in understanding the structure and function of many organisms. Particularly, it's a core aspect of metamerism, a type of segmentation where segments are similar in structure but have differentiated functions.

Examples of Segmentation

Earthworms, leeches, and a vast array of arthropods showcase this biological feature. The benefits of such a body plan include increased flexibility and locomotion, as well as the ability to localize damage to one segment without affecting the others. Metamerism is a highly evolved trait, primarily associated with the phylum Annelida, which includes segmented worms. It has played a critical role in the diversification of life forms, allowing for more complex and adaptable structures within organisms.

Comparative Anatomy

Comparative anatomy is the scientific study of the similarities and differences in the structures of different species. It is instrumental in understanding evolutionary relationships and how species have diverged from common ancestors over time. By comparing anatomical structures, such as skeletal bones or organ systems, biologists can infer how species are related and how they have adapted to their environments.

Clues to Evolutionary History

For example, the forelimbs of humans, whales, and bats have significantly different functions; however, they share a common structural pattern, suggesting a shared evolutionary origin. This field of study extends to the level of cellular and molecular structures as well, contributing to our understanding of developmental biology and genomics. Through the lens of comparative anatomy, we can thus unravel the historical and functional tapestry of life on Earth.