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

In a laboratory analysis of three unsegmented lower invertebrate specimens (XX, YY, and ZZ), the following structural features were recorded:

- Organism XX: Diploblastic construction, radial symmetry, and a gastrovascular cavity with a single opening.
- Organism YY: Triploblastic construction, acoelomate body plan, dorsoventrally flattened body, and flame cells for osmoregulation.
- Organism ZZ: Triploblastic construction, pseudocoelomate body cavity, cylindrical body shape, and a complete digestive tract with separate mouth and anus.

Which of the following options correctly identifies the phyla of organisms XX, YY, and ZZ, respectively?

  1. Coelenterata, Platyhelminthes, and NematodaAnswer
  2. B
    Porifera, Platyhelminthes, and Annelida
  3. C
    Coelenterata, Nematoda, and Platyhelminthes
  4. D
    Platyhelminthes, Coelenterata, and Nematoda

Answer

Organism XX belongs to Coelenterata (Cnidaria), Organism YY belongs to Platyhelminthes, and Organism ZZ belongs to Nematoda.
The correct response accurately pairs each organism with its phylum based on fundamental body plan criteria: Coelenterata are diploblastic with radial symmetry, Platyhelminthes are triploblastic acoelomates with flame cells, and Nematoda are triploblastic pseudocoelomates with a complete digestive tract.

Step-by-Step Solution

1
Analyze the anatomical characteristics of Organism XX.
Diploblastic germ layers (ectoderm and endoderm), radial symmetry, and a central gastrovascular cavity with one opening are diagnostic features of Coelenterata (Cnidaria).
Coelenterates are tissue-level organisms possessing two germ layers separated by mesoglea.
2
Analyze the anatomical characteristics of Organism YY.
Triploblastic germ layers, dorsoventral flattening, lack of a body cavity (acoelomate), and protonephridia (flame cells) define Platyhelminthes (flatworms).
Platyhelminthes are the simplest triploblastic animals but lack a secondary body cavity.
3
Analyze the anatomical characteristics of Organism ZZ.
Triploblastic construction with a pseudocoelom (fluid-filled body cavity not completely lined by mesoderm) and a complete alimentary canal (mouth to anus) define Nematoda (roundworms).
Nematodes represent an evolutionary advancement with a complete digestive tract and a pseudocoelomic cavity.

Key Concept

Structural organization, germ layers, body cavity types, and digestive completeness across lower invertebrate phyla.
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Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda