C, D and E only
The correct answer is A, B and E only.
These statements accurately describe molluscan protostomy, fundamental body plan, and developmental patterns, while C and D contain specific inaccuracies about radula structure and torsion direction.
Option Analysis
A, B and C only
A (protostome, reduced coelom), B (head-foot, visceral mass, mantle) correct, but C mischaracterizes radula as “muscular belt”—it’s a chitinous ribbon (radula) on a cartilaginous odontophore, not muscular. Incorrect.
B, C and D only
B correct, but C (radula error as above) and D (cephalopod torsion is 180° clockwise when viewed from apex, not anti-clockwise; creates definitive visceral/mantle reorientation) both wrong. Incorrect.
A, B and E only (Protostomes, body plan, protostome development)
A: Molluscs protostomes with schizocoelous coelom reduced to pericardial/gonadial/nephridial cavities. B: Classic tripartite body. E: Trochophore larvae, spiral cleavage, schizocoely—all definitive lophotrochozoan/protostome traits. Correct.
C, D and E only
C and D both incorrect (radula not muscular belt; torsion direction wrong), despite E correct. Incorrect.
Characteristics of Molluscs define the second-largest animal phylum with ~85,000 species, featuring soft bodies often shelled, occupying marine/freshwater/terrestrial niches through lophotrochozoan evolution.
Fundamental Body Plan
Molluscs possess head-foot (sensory/locomotory), visceral mass (organs), mantle (secretes shell, forms mantle cavity for respiration/excretion)—universal tripartite organization. Coelom reduced to pericardial, nephridial, gonadal cavities within hemocoel-dominated body.
Protostome Development
True protostomes with spiral cleavage, trochophore larvae, schizocoelous coelom formation. Mouth develops first from blastopore; definitive lophotrochozoan traits shared with annelids.
Specialized Structures
Radula: chitinous scraping ribbon with teeth, supported by odontophore (cartilaginous, not “muscular belt”). Cephalopod torsion: 180° clockwise rotation repositions anus anteriorly, funnel posteriorly.
