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

Match each lower invertebrate phylum listed on the left with its characteristic nervous system arrangement and structural organization on the right.

  • PoriferaAbsence of nerve cells, supported by a mineralized spicule or spongin skeleton at a cellular level of organization.
  • Coelenterata (Cnidaria)Diffuse nerve net embedded within mesoglea connecting tissue-level diploblastic layers.
  • PlatyhelminthesLadder-like nervous system with paired anterior cerebral ganglia in an acoelomate body.
  • NematodaCircumpharyngeal nerve ring with dorsal and ventral nerve cords in a pseudocoelomate body.

Answer

Porifera matches with absence of nerve cells and skeletal spicules; Coelenterata matches with a diffuse nerve net in mesoglea; Platyhelminthes matches with a ladder-like nervous system with paired ganglia; Nematoda matches with a circumpharyngeal nerve ring and longitudinal nerve cords.
Each phylum is correctly matched according to its level of neural centralization and body cavity plan: Porifera has no nerve cells, Coelenterata possesses a diffuse mesogleal nerve net, Platyhelminthes has a ladder-like nervous system with cerebral ganglia, and Nematoda has a circumpharyngeal nerve ring with a pseudocoelom.

Step-by-Step Solution

1
Analyze Porifera organizational features
Poriferans lack nerve tissues entirely and possess cellular-level organization supported by spicules.
Sponges are the most primitive lower invertebrates without nerve cells.
2
Identify Coelenterata nervous structure
Coelenterates feature a non-centralized nerve net situated within the mesoglea of their diploblastic body wall.
Cnidarians show tissue-level organization with diffuse neural networks.
3
Determine Platyhelminthes neural and coelomic organization
Platyhelminthes exhibit bilateral symmetry, paired anterior cerebral ganglia, ladder-like nerve cords, and an acoelomate body plan.
Flatworms represent the earliest triploblastic acoelomate animals showing true cephalization.
4
Match Nematoda characteristics
Nematodes possess a nerve ring around the pharynx, longitudinal nerve cords, and a fluid-filled pseudocoelom.
Roundworms possess a complete digestive tube surrounded by a pseudocoelom and a distinct circumpharyngeal nerve ring.

Key Concept

Neuro-structural evolutionary organization across lower invertebrate phyla
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Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda