Problem 147 - Objective Biology for NEET

Question

Larva of hemichordate is (a) Amphiblastula (b) Torneria (c) Ammocoete (d) Planula

Step-by-Step Solution

Answer

The correct answer is (b) Tornaria.

Step 1: Recall the Larval Form of Hemichordates

The Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the fossil record in the Lower or Middle Cambrian and include two main classes: Enteropneusta (Acorn Worms), and Pterobranchia. The larvae of many hemichordates are known as tornaria larvae. In appearance, tornaria larvae resemble the bipinnaria larvae of starfish, which is consistent with the idea that echinoderms and hemichordates are closely related.

Step 2: Match the Correct Larval Form

When we compare tornaria with the provided options: (a) Amphiblastula, (b) Tornaria, (c) Ammocoete, (d) Planula, we find that option 'b' Tornaria matches. Therefore, the answer is (b) Tornaria.

Key Concepts

Tornaria Larvae

Tornaria larvae are the early developmental stage of certain hemichordates, particularly those classified under Enteropneusta or acorn worms. These larvae are notable for their unique form, which includes a ciliated band used for swimming and feeding.
This feature of Tornaria larvae helps provide insights into their evolutionary relationship with echinoderms, such as starfish.

• Appearance: Tornaria larvae look quite similar to bipinnaria larvae of starfish. This resemblance hints at their shared evolutionary origins.
• Habitat: They are typically found in marine environments, where they float planktonically before settling down and transforming into adult forms.
• Function: The ciliated bands help them in swimming and capturing food particles from the surrounding water.

Understanding Tornaria larvae is crucial for comprehending the lifecycle and development of hemichordates.

Enteropneusta

Enteropneusta, more commonly known as acorn worms, are a fascinating group of marine organisms within the phylum Hemichordata. They serve as an important link in understanding chordate evolution.

• Body Structure: They possess a three-part body structure consisting of a proboscis, collar, and trunk. This simple anatomy is functionally adequate for their burrowing lifestyle.
• Feeding: Enteropneusts are primarily deposit feeders, sifting through sediment to find organic material. They also have filter-feeding capabilities due to their ciliated pharyngeal slits.
• Habitat: These organisms are typically found in soft marine sediments, from shoreline to abyssal depths.

Enteropneusta play a significant ecological role by recycling nutrients and helping maintain marine ecosystem health.

Pterobranchia

Pterobranchia are a tiny class of the phylum Hemichordata, consisting of small, colonial organisms. They are quite different from their Enteropneust relatives.

• Colonial Nature: Pterobranchs often live in colonies, housed within a protective mucus secretion called a coenecium.
• Body Plan: Unlike Enteropneusta, their bodies are divided into a stalk, a feeding arm, and a reproduction zooid, aiding in their specialized lifestyle.
• Feeding: These creatures use their tentacled arms for filter feeding, capturing plankton and other small particles from the water.

By studying Pterobranchia, researchers can gain insights into the diverse evolutionary paths within the Hemichordata phylum.

Echinoderms

Echinoderms are a vibrant marine phylum closely related to hemichordates due to their shared deuterostome development. These organisms have distinct traits which make them unique among marine life.

• Symmetry: Echinoderms exhibit radial symmetry as adults, typically five-pointed, which is a unique characteristic in the animal kingdom.
• Water Vascular System: They have a unique hydraulic system used for movement, feeding, and respiration, quintessential to their biology.
• Diversity: This phylum includes well-known species such as starfish, sea urchins, and sand dollars.

Understanding echinoderms is fundamental to evolutionary biology, as it provides insights into the early structural developments of complex life forms.