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Question

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

During a laboratory examination of lower invertebrates, a specimen is observed to have a triploblastic acoelomate body plan, a branched gastrovascular cavity with only one opening, and specialized flame cells for osmoregulation. Which phylum is characterized by these features?

  1. PlatyhelminthesAnswer
  2. B
    Nematoda
  3. C
    Coelenterata
  4. D
    Porifera

Answer

Platyhelminthes
The combination of a triploblastic acoelomate body structure, an incomplete digestive system (gastrovascular cavity), and flame cells for excretion uniquely defines members of the phylum Platyhelminthes.

Step-by-Step Solution

1
Analyze the germ layers and coelom status described in the stem.
The specimen is triploblastic (three germ layers) and acoelomate (lacks a body cavity).
This rules out diploblastic phyla (Coelenterata) and pseudocoelomate phyla (Nematoda).
2
Examine the gut completeness and excretory structures.
The specimen has an incomplete gut (gastrovascular cavity with a single opening) and possesses flame cells.
Flame cells (protonephridia) are the diagnostic excretory structures unique to phylum Platyhelminthes among lower invertebrates.

Key Concept

Structural characteristics and diagnostic organs of Phylum Platyhelminthes
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Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda