Examkin

Question

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

Lower invertebrates exhibit progressive evolutionary complexity in their level of organization, germ layers, and body cavity structure. Which of the following correctly pairs each lower invertebrate phylum with its characteristic body plan and anatomical configuration?

  • PoriferaCellular level of organization lacking distinct germ layers or true tissue differentiation
  • CoelenterataDiploblastic tissue level of organization surrounding a single gastrovascular cavity
  • PlatyhelminthesTriploblastic acoelomate body organization with dorsoventral flattening and an incomplete digestive tract
  • NematodaTriploblastic pseudocoelomate structure enclosed in a tough cuticle with a complete alimentary canal

Answer

Porifera corresponds to cellular-level organization lacking true tissues; Coelenterata corresponds to diploblastic tissue-level organization with a single gastrovascular cavity; Platyhelminthes corresponds to triploblastic acoelomate organization with an incomplete gut; Nematoda corresponds to triploblastic pseudocoelomate organization with a complete digestive tract.
Each phylum is accurately matched based on evolutionary progression: Porifera represents the cellular level without distinct germ layers; Coelenterata represents diploblastic tissue-level organization with a gastrovascular cavity; Platyhelminthes represents triploblastic acoelomate structure with an incomplete gut; and Nematoda represents triploblastic pseudocoelomate organization with a complete digestive tract and protective cuticle.

Step-by-Step Solution

1
Identify the level of organization and germ layer arrangement for Porifera.
Porifera consists of an aggregation of specialized cells without true tissues or germ layers.
Sponges are the most primitive lower invertebrates and operate at the cellular level.
2
Analyze Coelenterata for tissue layers and body cavity structure.
Coelenterates are diploblastic with radial symmetry and a gastrovascular cavity serving both mouth and anus functions.
Cnidarians develop ectoderm and endoderm separated by a jelly-like mesoglea.
3
Evaluate Platyhelminthes for embryonic germ layers, digestive tract, and body cavity.
Platyhelminthes are triploblastic, bilateral, acoelomate, and have an incomplete digestive system.
Mesoderm is present as solid parenchyma filling the space between the body wall and gut.
4
Evaluate Nematoda for body cavity type, digestive tract, and outer covering.
Nematodes are triploblastic, pseudocoelomate, covered by a cuticle, and feature a complete digestive system (mouth to anus).
The fluid-filled pseudocoelom provides a hydrostatic skeleton and permits a complete tube-within-a-tube alimentary canal.

Key Concept

Structural organization, germ layers, and body cavity evolution in lower invertebrates
Rate this question

Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda