Question

Which of the following is incorrect for Pheretima? (a) Genital papillae are present on \(17^{\text {th }}\) and \(19^{\text {th segmert }}\) (b) Male genital pores are present on \(18^{\text {th }}\) segment. (c) Clitellum is present on segments 24,25 and 26 . (d) Segments of earthworm are called somites.

Short answer

(d) is incorrect; earthworm segments are not called somites, they are simply called 'segments'.

Step-by-step solution

Understanding the Biological Terms

Familiarize with the biological terms mentioned such as 'genital papillae', 'male genital pores', 'Clitellum', and 'somites'. This will help in understanding the anatomy of Pheretima which is an earthworm species.

Researching each fact

Look up accurate biological information about Pheretima. Compare existing knowledge about earthworm anatomy to validate each of the statements given in the options.

Evaluating Each Statement

Assess each statement for its correctness based on the standard biological descriptions of Pheretima. A statement that does not match the scientific description of Pheretima's anatomy would be considered incorrect.

Identifying the Incorrect Statement

Using the knowledge of Pheretima's anatomy, identify the statement that is not aligned with the factual description. (a), (b), and (c) are correct; therefore (d) which claims that earthworm segments are called 'somites' is incorrect because they are actually called 'segments'.

Key concepts

Earthworm Anatomy

Earthworms, such as Pheretima, are intriguing creatures that have evolved to thrive in the soil. Their bodies are made up of ring-like segments called 'segments', not 'somites' as option (d) incorrectly states. These segments are covered in a protective cuticle and separated by septa, or internal walls, which help maintain the worm's structure. Each segment contains sets of muscles that allow the earthworm to move and burrow through the ground efficiently. Despite their simple appearance, earthworms possess a complex system of organs including a digestive system that runs the length of the body, a closed circulatory system, and a nervous system with a primitive brain. Delving deeper into their anatomy will reveal specialized structures like 'genital papillae' and the 'clitellum', which are crucial for reproduction.

An essential part of understanding earthworm anatomy is recognizing the important role these creatures play in aerating the soil and contributing to the decomposition process, which is vital for ecosystem health. Students should focus on visualizing the structure of the earthworm, noting how these anatomical features contribute to its ability to survive and function within its environment.

Genital Papillae

The 'genital papillae' are small, protruding structures found on the segments of the earthworm. Specifically, for the Pheretima, they are located on the 17th and 19th segments, as correctly mentioned in option (a). These papillae play a significant role in the earthworm's reproductive system. During mating, the papillae help in transferring sperm to the mating partner. This is part of the earthworm's fascinating reproductive capabilities, which are hermaphroditic, meaning each individual worm has both male and female reproductive organs.

In teaching about genital papillae, it's important to convey how these structures demonstrate the earthworm's efficiency in adapting reproductive strategies to their environment. For instance, their hermaphroditic nature allows earthworms to have a higher likelihood of successful reproduction since any encounter with another earthworm of the same species can potentially lead to fertilization. As an exercise improvement advice, visual aids such as diagrams or models can significantly enhance the comprehension of where these papillae are located and how they function during the reproductive process.

Clitellum

The clitellum is a distinctive, thickened, glandular section of the earthworm's body, which is involved in reproduction. For Pheretima, as correctly stated in option (c), the clitellum is found on segments 24, 25, and 26. This band-like region secretes mucus during mating to form a cocoon into which eggs and sperm are deposited. Once the earthworm withdraws from this cocoon, it closes off to create a nurturing environment for the developing embryos. Besides being a reproductive organ, the clitellum is also an easily identifiable feature used to determine an earthworm’s level of maturity.

Understanding the role of the clitellum helps students appreciate the unique reproductive habits of earthworms. For clarity in education, highlighting the differences between the clitellum and other parts of the body can be beneficial. In particular, illustrating the changes in texture and color can help to solidify the recognition of the clitellum in anatomical studies. Encouraging students to physically examine earthworm specimens, if possible, can provide a hands-on experience that cements the understanding of the clitellum's location and function.