Question

Which of the following is/are diagnostic morphological feature(s) of brachiopods?

• A. Skeleton has pentameral symmetry
• B. Dorsal valve
• C. Thoracic segments
• D. Deltidial plate

Hint:

Think about what body plan brachiopods actually have (two valves, a pedicle opening) versus features that belong to echinoderms or trilobites.

Answer 1

The Correct Option is B, D

Step 1: Recall the basic body plan of a brachiopod.
A brachiopod is a marine animal with a shell made of two valves, a dorsal valve and a ventral valve. Unlike a clam or a mussel, the two valves of a brachiopod are not mirror images of each other. Instead, each single valve is itself bilaterally symmetric.

Step 2: Check pentameral symmetry.
Pentameral, or five-fold, symmetry is the hallmark of echinoderms such as starfish and crinoids, not of brachiopods. A brachiopod shell does not show this five-part pattern. Option (A) is incorrect.

Step 3: Check the dorsal valve.
The dorsal valve, together with the ventral valve, is exactly what defines a brachiopod shell. The two valves differ in size and shape, and this valve arrangement, along with the hinge and the pedicle opening, is used to classify and identify brachiopod species. Option (B) is correct.

Step 4: Check thoracic segments.
Thoracic segments belong to the body plan of trilobites, which are divided into a head or cephalon, a segmented middle or thorax, and a tail or pygidium. Brachiopods have no such segmented thorax. Option (C) is incorrect.

Step 5: Check the deltidial plate.
In many articulate brachiopods, small plates called deltidial plates partly close the delthyrium, the triangular opening below the beak of the ventral valve through which the pedicle passes. The shape and presence of these plates is a standard diagnostic feature used in brachiopod taxonomy. Option (D) is correct.

Step 6: Final answer.
The dorsal valve and the deltidial plate are true diagnostic features of brachiopods, while pentameral symmetry belongs to echinoderms and thoracic segments belong to trilobites.
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