Question

Which is the most recent lineage in the evolution of Phylum Nematoda as per the SSU rDNA based classification system proposed by De Ley and Blaxter in 2002?

• A. Triplonchida
• B. Dorylaimida
• C. Rhabditida
• D. Tylenchida

Hint:

Remember that the molecular classification by De Ley and Blaxter (2002) grouped traditional orders like Tylenchida into the order Rhabditida, making Rhabditida the largest and most derived order within the Chromadorea.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The classification of the Phylum Nematoda was updated by De Ley and Blaxter (2002) using small subunit ribosomal DNA (SSU rDNA 18S rRNA) sequence data.
This molecular framework replaced older morphological systems, reorganizing the phylum into three major classes: Enoplea, Dorylaimea, and Chromadorea.

Step 2: Detailed Explanation:
In the system proposed by De Ley and Blaxter, the classes Enoplea and Dorylaimea represent basal, early-diverging, and ancestral lineages of nematodes.
These classes contain orders such as Triplonchida and Dorylaimida.
In contrast, the class Chromadorea represents the most derived and evolutionary recent group of nematodes.
Within the Chromadorea, the order Rhabditida is defined broadly to include several groups that were previously classified as separate orders, such as Tylenchida, Aphelenchida, and Strongylida.
In this system, Tylenchida was reclassified as a suborder (Tylenchina) within the order Rhabditida.
The order Rhabditida contains highly specialized plant-parasitic, animal-parasitic, and free-living bacterial-feeding nematodes.
This represents the most derived and evolutionary recent lineage in the phylum.
Therefore, Rhabditida is the correct classification for the most recent lineage among the choices.

Step 3: Final Answer:
Rhabditida represents the most derived and evolutionary recent lineage in the De Ley and Blaxter (2002) molecular classification.
Thus, the correct option is 3.