PG TRB ZOOLOGY | Unit I - ANIMAL DIVERSITY AND PHYLOGENY | Torsion in Gastropods.

PG TRB ZOOLOGY ONLINE TEST / QUIZ AS PER LATEST SYLLABUS | Unit I - ANIMAL DIVERSITY AND PHYLOGENY | Torsion in Gastropods.

1. What is the primary cause of torsion in gastropods?

Asymmetrical growth of the larva A single muscle contracting on the left side Torsion of the body whorl Contraction of the columellar muscle

2. During torsion, the anus and mantle cavity move from a posterior to an anterior position. This is an example of:

Cephalization Detorsion Coiling Developmental metamorphosis

3. The process of torsion is completed in a gastropod larva within a very short period of time. This stage is known as the:

Veliger stage Trochophore stage Glochidium stage Bipinnaria stage

4. Which part of the gastropod body is primarily involved in the 180° counter-clockwise rotation during torsion?

The shell The visceral mass The head The foot

5. What is the most significant disadvantage of torsion for a gastropod?

Increased risk of predation Fouling of the mantle cavity Reduced mobility Inefficient respiration

6. The columellar muscle's contraction on the left side, pulling the visceral mass over the head, is part of the:

First stage of torsion Second stage of torsion Detorsion Coiling process

7. The evolutionary advantage of torsion is believed to be:

Protection of the gills from sediment Better balance and stability in the shell Enhanced sensory organs at the anterior end The ability to retract the head into the shell first

8. What is the result of torsion on the nervous system of the gastropod?

Elongation of the pleurovisceral loop Fusion of the cerebral ganglia Formation of a figure-of-eight nervous system A decrease in the number of ganglia

9. The process where the gastropod reverses the effects of torsion, often seen in Opisthobranchs, is known as:

Dextral coiling Torsional reversal Detorsion Torsion itself, but in the opposite direction

10. The repositioning of the mantle cavity to the anterior allows gastropods to:

Detect food sources more effectively Have better shell ventilation during movement Improve respiratory efficiency All of the above

11. In which group of gastropods is the phenomenon of detorsion most commonly observed?

Prosobranchia Pulmonata Opisthobranchia Archaeogastropoda

12. The larval stage of a gastropod, where torsion typically occurs, is characterized by a ciliated swimming organ called the:

Velum Operculum Foot Mantle

13. What is the name of the muscle that contracts to pull the visceral mass and mantle forward during torsion?

Retractor muscle Columellar muscle Adductor muscle Mantle muscle

14. Torsion results in the mantle cavity opening to the anterior, leading to a condition known as:

Protobranchiate Euthyneury Asymmetrical coiling Eutorsion

15. The "fouling" problem resulting from torsion refers to:

The accumulation of waste in the digestive gland The discharge of feces and urine into the mantle cavity The inability to retract the head into the shell The shell becoming heavy with sediment

16. What evolutionary modification has been observed in some gastropods to overcome the "fouling" problem?

A longer digestive tract The presence of a special filtering organ Development of an anal siphon or slit in the shell A change in feeding habits

17. In the Class Gastropoda, the primitive group with a symmetrically coiled shell and a posterior mantle cavity is represented by which subclass?

Prosobranchia Opisthobranchia Pulmonata Monoplacophora

18. The change in the position of the anus, gills, and osphradium is a direct consequence of:

Torsion Coiling Shell development Muscle atrophy

19. What is the name of the group of gastropods that have undergone complete detorsion, resulting in a secondary loss of the coiled shell and mantle cavity?

Prosobranchs Archaeogastropods Nudibranchs Pulmonates

20. The twisting of the nervous system and gut during torsion is a key feature that distinguishes gastropods from other classes of molluscs. This condition is also known as:

Streptoneury Euthyneury Dextral coiling Sinistral coiling

21. The most widely accepted hypothesis for the adaptive value of torsion is that it is a larval adaptation for:

A more efficient feeding mechanism Protection from predation by allowing the head to be retracted first Improved streamlining for faster swimming Maintaining a stable center of gravity

22. Which of the following is NOT a consequence of torsion?

A loss of symmetry in the visceral organs The formation of a coiled shell The repositioning of the mantle cavity The twisting of the pleurovisceral nerve loop

23. In some gastropods, a second, less pronounced torsion may occur. This is often associated with the:

Shell coiling in a different direction Development of a pulmonary sac Repositioning of the gills Atrophy of the right ctenidium

24. The term "Euthyneury" describes a condition in which the nervous system is untwisted. This is a characteristic of which gastropod subclass?

Prosobranchia Patellogastropoda Vetigastropoda Heterobranchia

25. Torsion in gastropods is considered to be a key evolutionary innovation that allowed them to colonize a wide range of habitats. This is primarily due to:

The development of a stronger shell An improved defense mechanism Greater efficiency in reproduction The ability to filter feed more effectively

26. In the process of torsion, the larval anus moves from the posterior to the anterior. This shift is accompanied by the twisting of which of the following structures?

The esophagus The reproductive ducts The gut and the nerve cords The operculum

27. The development of a single, powerful columellar muscle is a key event in gastropod torsion. This muscle is attached to the:

Mantle and foot Shell and foot Head and foot Shell and mantle

28. The condition of "fouling" is a major problem for primitive gastropods. Which of the following is NOT an adaptation to minimize this problem?

Loss of the right gill Shell slits and foramina Development of a siphon Torsion itself

29. The most significant consequence of the 180° rotation of the visceral mass is the change in the relative position of the anus and gills, which leads to:

The gills being positioned posteriorly to the anus The anus being positioned anteriorly, near the head A complete fusion of the gills The disappearance of the anus

30. Torsion is a unique developmental feature of the class Gastropoda, which involves a counter-clockwise rotation of the visceral mass by:

90 degrees 360 degrees 180 degrees 270 degrees

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