Question

Assertion: Ascidia belong to sub - phylum urochordata. Reason: Notochord is present in tail of larva stage.

Short answer

Yes, the assertion is correct. Ascidia do belong to the sub-phylum Urochordata and develop a notochord in the tail during their larval stage.

Step-by-step solution

Define the categories

Firstly, confirm the classification of Ascidia. Urochordata is a sub-phylum of Chordata, which are animals with notochords. Ascidia is indeed part of the Urochordata. Thus, the first part of the assertion is correct.

Confirm the developmental stage

Next, confirm the claim that notochords are present in the tail of the larval stage of Ascidia. Urochordates are characterized by the presence of a notochord at some stage of their development. For Ascidia, the notochord is indeed present in the tail during the larval stage.

Conclude the connection

Since both the taxonomy and developmental characterization match up, it can be concluded that the statement 'Ascidia belong to sub - phylum Urochordata. Notochord is present in tail of larva stage.' is valid.

Key concepts

Ascidia

Ascidia is a fascinating organism that belongs to the sub-phylum Urochordata. These creatures are often colloquially referred to as sea squirts due to their ability to expel water through their siphons when disturbed. Ascidia are marine invertebrates typically found attached to rocks, shells, or pilings in marine environments. They have a sac-like body structure, engulfing water and filtering plankton and organic particles for nutrition.

Despite their simple appearance, Ascidia play a significant role in the ecosystem as filter feeders, helping to maintain water quality and clarity. Their life cycle includes both a mobile larval form and a sedentary adult form, highlighting a fascinating transformation that emphasizes the adaptive strategies of marine life. Ascidia serve as an excellent representative of the urochordates, demonstrating unique biological characteristics representative of this sub-phylum.

Notochord

The notochord is a flexible, rod-like structure that is a key feature of the chordate group of animals, to which Urochordata, including Ascidia, belong. In most chordates, it acts as a skeletal support structure, and in many species, it is present only during embryonic development. However, in the case of tunicates like Ascidia, the notochord is present only during the larval stage. Located in the tail, it contributes to the swimming ability of the larvae.

This structure is crucial for the movement of the larvae, which need to find suitable substrates to attach themselves as they transition into adulthood. Once they attach and undergo metamorphosis, the notochord is lost, and they develop into their adult form. This transformation highlights the evolutionary significance of the notochord as a crucial developmental feature in chordate life cycles.

Larval Stage

The larval stage of Ascidia, and indeed for many Urochordates, is a critical phase of development. During this stage, the organism possesses features typical of chordates, such as the notochord and a dorsal nerve cord. The larvae are free-swimming and actively seek out a stable substrate in their marine environment.

Larvae use their tails, powered by the notochord, to navigate through the water. This larval mobility is key to their survival, as it allows them to find optimal locations for attachment, ensuring suitable conditions for the next stage of development. Once a secure spot is identified, the larvae attach head-first and undergo a dramatic transformation into the adult form, losing many of their chordate features. This transformation illustrates the lifecycle adaptations tunicates have developed to thrive in marine ecosystems.

Chordata Classification

Chordata is a large and diverse phylum of animals including vertebrates, cephalochordates, and urochordates. A defining characteristic of this phylum is the presence of a notochord at some stage of development. The sub-phylum Urochordata, also known as Tunicata, includes organisms like Ascidia. They exhibit the chordate features during their larval stage, such as the notochord and nerve cord.

These features are critical for classifying Ascidia within the Chordata phylum. Despite losing some chordate traits as adults, this larval phase ensures they are grouped within this broad classification. Understanding chordate classification helps recognize the evolutionary connections and biological complexity inherent within this diverse group of organisms, showcasing the continuum of life forms from simple tunicates to complex vertebrates.