Problem 41 - Objective Biology for NEET

Question

In sponges, the commonly seen larva are (a) Amphiblastula (b) Parenchymula (c) Planula (d) Both (a) and (b)

Step-by-Step Solution

Answer

(d) Both (a) and (b)

Step 1: Understand Larval Forms in Sponges

The first step involves understanding the different types of larvae that can be seen in sponges. Amphiblastula and parenchymula are two types of larvae that are found in various kinds of sponges. Note that planula larva is found in Cnidarians, not Sponges.

Step 2: Compare with Options

On comparing our knowledge about sponge larvae with the given options, we can clearly see that both Amphiblastula and Parenchymula are correct.

Step 3: Select the Correct Answer

Since Amphiblastula and Parenchymula are present in sponges, and both are listed as separate options as well as collectively in option (d), we select option (d) as our final answer.

Key Concepts

Amphiblastula

Amphiblastula larvae are fascinating because of their unique structure. They are typically found in certain calcareous sponges, which are part of a diverse group of sea creatures. Amphiblastula larvae have distinct cell types that make them easily recognizable. The larvae have two main regions:

• One half is composed of flagellated cells, which help in mobility allowing the larva to swim through water.
• The other half consists of non-flagellated cells that may play various roles in development.

The arrangement of these cells is critical for their movement and eventual settlement on a surface where they develop into adult sponges. During the development phase, the amphiblastula hatches out from the parent sponge and disperses into the water, searching for a suitable surface to attach itself to and begin its transformation into a mature sponge.

Parenchymula

Parenchymula larvae, another crucial form of sponge larvae, are characterized by their simple yet effective design. Unlike amphiblastula, parenchymula larvae are more common in demosponges, which make up the majority of sponge species.

Parenchymula larvae are entirely covered with flagella, small hair-like structures that help them swim in the water.
These larvae are free-swimming and play a significant role during the early dispersion phase. This is vital as it allows the larvae to find a surface to settle on. Once settled, the parenchymula will undergo significant changes, developing into the complex body structure of an adult sponge. This phase of movement and settlement is essential to ensure the spread and survival of sponge species across various marine environments.

Planula

Planula larvae belong to a different group entirely—those found in cnidarians, such as jellyfish, corals, and sea anemones. These larvae differ from sponge larvae, like amphiblastula and parenchymula, in several ways.

The planula larvae are typically oblong and ciliated, which aids them in swimming. They are free-swimming and can travel quite some distance in the ocean. This mobility helps distribute cnidarian species across a wide range of marine environments. After swimming through the ocean, planula larvae find a suitable surface to settle and transform into a polyp or other life forms, depending on the species.

The planula is a critical phase in the life cycle of cnidarians, allowing for genetic variation and wide population dispersal, which helps these species to thrive in various ecological niches.