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Question

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

Match each lower invertebrate group listed on the left with its corresponding specialized cellular mechanism or tissue-level body plan characteristic on the right.

  • PoriferaChoanocytes with flagellated collars that maintain Unidirectional water currents through ostia for filter feeding
  • Coelenterata (Cnidaria)Specialized cnidocytes housing stinging nematocysts triggered for prey capture and defense
  • PlatyhelminthesSolid mesenchymatous parenchyma tissue filling the blastocoel between the gut and body wall in an acoelomate plan
  • NematodaHigh-pressure fluid pseudocoelom acting as a hydrostatic skeleton working exclusively against longitudinal muscles

Answer

Porifera matches choanocytes with flagellated collars; Coelenterata matches specialized cnidocytes with nematocysts; Platyhelminthes matches solid mesenchymatous parenchyma tissue; Nematoda matches high-pressure fluid pseudocoelom acting as a hydrostatic skeleton.
Each lower invertebrate phylum displays distinct cellular and structural specializations: Porifera utilize flagellated choanocytes to drive water currents; Coelenterata deploy explosive cnidocytes housing nematocysts; Platyhelminthes possess an acoelomate body plan packed with mesenchymatous parenchyma tissue; and Nematoda utilize a fluid-filled hydrostatic pseudocoelom acting against longitudinal muscles for locomotion.

Step-by-Step Solution

1
Analyze cellular adaptations of Porifera
Porifera (sponges) lack true tissues and rely on choanocytes (collar cells) to circulate water through internal canals for suspension feeding.
Choanocytes are diagnostic of Phylum Porifera.
2
Identify defense and feeding mechanisms of Coelenterata
Coelenterates (cnidarians like Hydra and jellyfish) are characterized by diploblastic organization with cnidocytes housing stinging nematocysts.
Cnidocytes/nematocysts are unique to Phylum Coelenterata.
3
Evaluate body cavity and tissue organization of Platyhelminthes
Platyhelminthes (flatworms) are triploblastic but acoelomate, meaning the space between the body wall and endodermally derived digestive tract is packed solid with parenchyma tissue.
Acoelomate parenchyma arrangement distinguishes flatworms from pseudocoelomates.
4
Determine locomotory and hydrostatic features of Nematoda
Nematoda (roundworms) possess a persistent blastocoel (pseudocoelom) filled with fluid under pressure. Combined with a tough cuticle and lack of circular muscle, contraction of longitudinal muscles produces thrashing motion.
Pseudocoelomic hydrostatic skeleton combined with longitudinal muscle action is characteristic of nematodes.

Key Concept

Structural and cellular diagnostic features of lower invertebrate phyla (Porifera, Coelenterata, Platyhelminthes, Nematoda)
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Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda