Brachiopod Morphological Features Explained

This solution identifies the key diagnostic morphological features specific to brachiopods from the given options.

Analyzing Brachiopod Characteristics

• Dorsal valve (Option B): Brachiopods are characterized by having two distinct valves: a dorsal valve and a ventral valve. This fundamental bilateral symmetry through the valves is a defining trait.
• Deltidial plate (Option D): The deltidial plate is a small, often fused, calcareous plate found in the posterior (umbonal) region of the ventral valve of many brachiopod species. Its presence and structure are important diagnostic features.
• Pentameral symmetry (Option A): Radial symmetry, specifically pentameral (five-part) symmetry, is characteristic of echinoderms (like starfish), not brachiopods.
• Thoracic segments (Option C): Segmented bodies, including thoracic segments, are typical features of arthropods (like insects and crustaceans), not brachiopods.

Conclusion on Diagnostic Features

Based on characteristic anatomy:

• The presence of a distinct dorsal valve is a fundamental feature of brachiopod morphology.
• The deltidial plate in the ventral valve is another significant diagnostic feature aiding in brachiopod identification.

Therefore, options B and D represent the diagnostic morphological features of brachiopods.