Question

In which of the following nematode, phasmids are absent?

• A. Hoplolaimus
• B. Criconema
• C. Tylenchorhynchus
• D. Rotylenchus

Hint:

Within the order Tylenchida, ring nematodes belonging to the family Criconematidae (such as Criconema) are characterized by the absence of functional phasmids.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Phasmids are paired, unicellular caudal sensory organs found in the posterior region of certain nematode classes.
Historically, nematodes were divided into the classes Secernentea (phasmidians) and Adenophorea (aphasmidians) based on the presence or absence of these structures.

Step 2: Detailed Explanation:
While the classification system has evolved, the presence or absence of functional phasmids remains an important diagnostic feature:
1. Hoplolaimus (A), Tylenchorhynchus (C), and Rotylenchus (D): These are typical tylenchid nematodes belonging to the families Hoplolaimidae and Dolichodoridae.
They possess distinct, functional, easily visible phasmids (sometimes enlarged into scutella, as in Hoplolaimus).
2. Criconema (B): This genus belongs to the family Criconematidae (ring nematodes).
In this family, the posterior sensory structures (phasmids) are absent or highly reduced and non-functional.
This is a key diagnostic feature of the family Criconematidae within the order Tylenchida.

Step 3: Final Answer:
Therefore, phasmids are absent in the genus Criconema.