The Question is from neet-zoology animal-kingdom chordata, and it was created by the author A SUBRAMANYAM

Question

Which unique characteristic differentiates Urochordates from other chordates, disappearing during their larval stage?

A SUBRAMANYAM · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
	**Primary Concept**: Chordate Characteristics and Urochordate Development
	**Related Topics**: Invertebrate Zoology, Phylogeny, Metamorphosis
	**Prerequisites**: Basic understanding of Chordate features and Urochordate life cycle.
## SOLUTION PATHWAY
**Given Information**:
	Urochordates possess all four key chordate characteristics at some point in their life cycle.
	The question asks about a characteristic *unique* to Urochordates among chordates, and that *disappears* during their larval stage.
**Method & Steps**:
	1. Recall the four chordate characteristics: Notochord, Dorsal hollow nerve cord, Pharyngeal slits, and Post-anal tail.
		Reasoning: These are the defining features of the phylum Chordata.
	2. Analyze how these characteristics are present in Urochordates, specifically focusing on the larval and adult stages.
		Working:  Urochordates possess all four characteristics during their larval stage. In their adult, sessile form, they retain only the pharyngeal slits.
		Key Point: The notochord is present *only* in the larval stage of Urochordates and is crucial for their free-swimming lifestyle. This is a key distinction from other chordates.
	3. Identify the characteristic that disappears during the larval stage and is unique in its absence in adult Urochordates compared to other chordates.
		Result: The notochord disappears during metamorphosis into the adult form.
		Verification:  Adult Urochordates are sessile filter feeders and do not require the structural support of a notochord, unlike other chordates which generally retain it throughout their lives.
## OPTION ANALYSIS
[A] ✓: The notochord is present in the larval stage of Urochordates, enabling swimming. It disappears during metamorphosis into the sessile adult stage. This is unlike other chordates, which largely retain the notochord throughout their life. 
[B] :x: The dorsal hollow nerve cord is present in the larval stage and is reduced to a simple ganglion in the adult Urochordate. While reduced, it is still present, unlike the notochord.  Other chordates retain the nerve cord throughout life.
[C] :x: Pharyngeal slits are present in both larval and adult Urochordates, serving a filter-feeding function. This feature is shared with other chordates at some stage in their life cycle.
[D] :x: The post-anal tail is present in the larval stage, facilitating movement. It is lost during metamorphosis. However, the loss of the post-anal tail is not unique to Urochordates as some other chordates also lose it during development (e.g., frogs).
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing the presence/absence of features in the larval vs. adult stages: Remember to focus on the *disappearance* of the characteristic during the *larval* stage.
		2. Not considering the *uniqueness* to Urochordates: The question specifically asks about a characteristic that *differentiates* Urochordates from *other* chordates.
	**Quick Tips**:
		1. Remember the key feature of Urochordate metamorphosis: The dramatic change from a free-swimming larva with all chordate features to a sessile adult with only pharyngeal slits.
		2. Visualize the larval Urochordate as a 'tadpole-like' creature with a notochord and tail, and the adult as a 'sac-like' filter feeder without these features.

A SUBRAMANYAM · Answer

The correct Option is "Notochord"

A SUBRAMANYAM · Answer

Dorsal hollow nerve cord

A SUBRAMANYAM · Answer

Pharyngeal slits

A SUBRAMANYAM · Answer

Post-anal tail

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