Planula larva

Definition

The planula larva is a free-swimming, ciliated larval stage of cnidarians that develops from the fertilized egg and eventually settles to form a polyp. This stage is crucial for the life cycle of cnidarians, as it allows for dispersal and colonization of new habitats. The planula's ability to swim and its ciliated surface enable it to move through the water, increasing its chances of finding suitable substrate to settle and grow into the adult form.

5 Must Know Facts For Your Next Test

1. Planula larvae are typically covered in cilia, which help them swim and navigate through their aquatic environment.
2. Once a planula larva finds a suitable surface, it will settle down and undergo metamorphosis into a polyp, starting its sessile life.
3. Planula larvae can be produced asexually or sexually, depending on the reproductive strategy of the parent organism.
4. This larval stage plays a significant role in the dispersal of cnidarian species, allowing them to colonize new areas and avoid overcrowding.
5. The planula's morphology varies between different cnidarian species, reflecting their adaptations to specific environments.

Review Questions

• How does the planula larva contribute to the life cycle of cnidarians, and what is its role in dispersal?
  • The planula larva serves as a critical phase in the life cycle of cnidarians by providing a means of dispersal away from the parental organism. After fertilization, the planula swims freely through the water, which allows it to cover distances and find new habitats. Once it locates a suitable substrate, it settles down and transforms into a polyp, marking the beginning of its sessile life stage. This movement helps prevent overcrowding and promotes genetic diversity within cnidarian populations.
• Discuss the differences between planula larvae and other life stages of cnidarians, particularly polyps and medusae.
  • Planula larvae are distinct from polyps and medusae in both structure and function. While planulae are free-swimming and covered in cilia for locomotion, polyps are stationary organisms anchored to a substrate with upward-facing tentacles for feeding. In contrast, medusae are free-floating and bell-shaped, adapted for swimming and reproduction. Each stage has evolved to serve specific roles within the life cycle: dispersal for planulae, feeding and growth for polyps, and reproduction for medusae.
• Evaluate the significance of the planula larva's ciliated structure in terms of environmental adaptation and survival strategies.
  • The ciliated structure of the planula larva is significant for its environmental adaptation and survival strategies. The presence of cilia enhances its mobility in water, enabling it to actively seek out suitable habitats while also increasing its chances of escaping predators. This adaptability is crucial for the survival of young cnidarians, allowing them to colonize new environments effectively. Additionally, as planulae can be produced either sexually or asexually depending on environmental conditions, this flexibility ensures that cnidarians can thrive across diverse ecosystems.

Related terms

Cnidocytes: Specialized cells found in cnidarians that contain stinging structures called nematocysts, used for capturing prey and defense.

Polyp:

The sessile life stage of cnidarians, characterized by a cylindrical body and tentacles that face upwards, typically attached to a substrate.

Medusa: The free-swimming, bell-shaped life stage of cnidarians that reproduces sexually, releasing gametes into the water.