Problem 155 - Objective Biology for NEET

Question

Urochordata and cephalochordate are referred as (a) Non-chordates (b) Vertebrates (c) Protochordates (d) All of these

Step-by-Step Solution

Answer

The correct answer is (c) Protochordates.

Step 1: Understand The Terms

Urochordata and cephalochordate are under the Chordata phylum which encompasses vertebrates (animals with backbones), and two types of invertebrates: urochordates (like marine creatures tunicates) and cephalochordates (like lancelets). Although they are part of the chordates, they are not vertebrates, as vertebrates are a subgroup of chordates that has a backbone. They are also not non-chordates as they do fall under the Chordata phylum.

Step 2: Identify The Correct Class

By understanding what each term signifies, it's clear that these two terms fall under the category of protochordates. Protochordates are invertebrate animals that are closely related to vertebrates. They do not have a backbone, but they do possess some characteristics of the Chordata phylum during some stage of their life. Both Urochordata and cephalochordate are protochordates.

Key Concepts

Urochordata

Urochordata, also known as tunicates, are fascinating marine organisms that belong to the Chordata phylum. This group includes soft-bodied species such as sea squirts. While they may look quite different from other chordates, they share fundamental traits of the phylum.
During their larval stage, tunicates exhibit clear chordate characteristics like a notochord, a dorsal nerve cord, and pharyngeal slits. However, as they transition to adulthood, they lose many of these features, such as the notochord and nerve cord.

• Larval Form: The larvae are free-swimming and use their chordate features for mobility and structure.
• Adult Form: As adults, they tend to be sessile, attaching themselves to stationary surfaces underwater.

Urochordates have a unique life cycle that highlights the evolutionary pathway from basic chordate features to more complex forms.

Cephalochordate

Cephalochordates, often known as lancelets or amphioxus, represent another intriguing subgroup of protochordates within the Chordata phylum. Unlike urochordates, cephalochordates maintain their chordate characteristics throughout their life cycle.
Lancelets are small, elongated, and somewhat fish-like in appearance, which mirror more closely the archetype of early chordates. They retain a notochord, a dorsal nerve cord, and pharyngeal slits throughout their life, which play key roles in their growth and function.

• Notochord: Provides a flexible support structure, analogous to a backbone in vertebrates.
• Dorsal Nerve Cord: Facilitates nerve signal transmission, necessary for bodily function.
• Pharyngeal Slits: Help in filter-feeding, a primary mode of nutrition for these creatures.

This group underscores the spectrum of chordate development, bridging the gap between typical invertebrates and vertebrates.

Chordata Phylum

The Chordata phylum is a major classification in the animal kingdom that includes both vertebrate and invertebrate animals. Organisms in this phylum are united by specific features present at some stage of their life cycle, including a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail.
While vertebrates, such as mammals, birds, and fish, are well-known members of this phylum due to their defined backbones, two key invertebrate groups also exist: Urochordata and Cephalochordate, collectively known as protochordates. These protochordates, although lacking a backbone, showcase crucial developmental aspects of chordates.

• Notochord: Serves as a versatile axis of support and is a precursor to the vertebral column found in vertebrates.
• Dorsal Nerve Cord: Differentiates into the central nervous system in more derived chordates.
• Presence in Development: Many features are most prominent during embryonic development, particularly in humans and other vertebrates.

The Chordata phylum is diverse and plays a significant role in understanding evolutionary biology and the origins of complex life forms.