Question

In nematode taxonomy, the de Man's ratio c' is

• A. body length tail length
• B. body length oesophageal length
• C. tail length body width at anus
• D. tail length maximum body width

Hint:

To avoid confusion among the de Man's ratios:
- Primeless indices (\( a \), \( b \), \( c \)) always use the total body length in the numerator.
- Primed indices (like \( c' \)) use a specific organ measurement (like tail length) in the numerator to establish a local proportional relationship.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
In nematode taxonomy and systematics, morphometric measurements are essential for characterizing and identifying species.
To standardize these measurements and account for variation in individual specimen sizes, Johannes Govertus de Man (1884) introduced a system of ratios, known as the de Man's indices or de Man's formula.
These ratios express key anatomical proportions as mathematical indices, facilitating comparative studies between species.

Step 2: Detailed Explanation:
The standard de Man's indices are defined as follows:
- Index \( a \): The ratio of total body length to the maximum body width.
\[ a = \frac{\text{Total Body Length}}{\text{Maximum Body Width}} \] - Index \( b \): The ratio of total body length to the esophageal (oesophageal) length (measured from the anterior tip to the junction of the esophagus and the intestine).
\[ b = \frac{\text{Total Body Length}}{\text{Oesophageal Length}} \] - Index \( c \): The ratio of total body length to the tail length (measured from the anus or cloaca to the terminus of the tail).
\[ c = \frac{\text{Total Body Length}}{\text{Tail Length}} \] In addition to these primary ratios, nematologists introduced modified indices to provide better diagnostic resolution, particularly for species identification.
One of the most important modified ratios is \( c' \).
The ratio \( c' \) is defined as the tail length divided by the body width at the anus (anal body width, abbreviated as ABW) for females, or the body width at the cloaca (cloacal body width) for males.
\[ c' = \frac{\text{Tail Length}}{\text{Body Width at Anus/Cloaca}} \] This ratio is highly useful because it remains relatively constant during the nematode's development and is less influenced by physiological changes (such as egg production or feeding state) than the total body length.
Therefore, option (C) is the correct definition.

Step 3: Final Answer:
The de Man's ratio \( c' \) represents the tail length divided by the body width at the anus.