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Question

Difficulty: MediumLower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda

Members of the phylum Nematoda, such as *Ascaris lumbricoides*, are able to inhabit the human digestive tract without being destroyed by host digestive enzymes. Which outer protective structure provides this adaptive advantage?

  1. A tough, non-living cuticle covering the body wallAnswer
  2. B
    A ciliated cellular epidermis containing rhabdites
  3. C
    A calcareous exoskeleton composed of spicules
  4. D
    A syncytial layer of flagellated collar cells

Answer

A tough, non-living cuticle covering the body wall
Parasitic nematodes such as *Ascaris lumbricoides* possess a thick, non-living cuticle secreted by the hypodermis. This cuticle acts as a physical and chemical barrier that resists host digestive enzymes and hydrostatic pressure within the intestine.

Step-by-Step Solution

1
Identify the phylum and physiological challenge described in the stem
The organism belongs to Phylum Nematoda (*Ascaris lumbricoides*) living inside the host's gut environment containing digestive enzymes.
Parasitic roundworms require specific structural adaptations to survive harsh host biochemical conditions.
2
Evaluate the body wall protective features of Nematoda compared to other lower invertebrates
Nematodes possess a thick, flexible, non-living cuticle secreted by the hypodermis that resists enzymatic breakdown.
Structures like ciliated epidermis (Platyhelminthes), spicules (Porifera), or choanocytes (Porifera) belong to other lower invertebrate groups and do not serve this protective function.

Key Concept

Parasitic adaptations and outer body layer of Nematoda
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Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda