🪸 Introduction

Phylum Ctenophora (Comb Jellies) Ctenophores are commonly known as sea walnuts or comb jellies.

  • Comb Plates: The body bears eight external rows of ciliated comb plates. These comb plates help in locomotion.

  • Bioluminescence: Ctenophores are well-known for their property of bioluminescence (the ability of a living organism to emit light).

  • Tentacles & Feeding: Tentacles may be present. Unlike Cnidarians, they capture food using specialized sticky cells called colloblasts (lassocells) instead of cnidoblasts.

  • Examples: Pleurobrachia, Ctenoplana.

🧬 General Characteristics

  • Habitat: They are exclusively marine.
  • Symmetry: Exhibit radial symmetry.
  • Germ Layers: They are diploblastic organisms.
  • Level of Organisation: They have the tissue level of organisation.
  • Digestion: Digestion is both extracellular and intracellular.

🌊 Reproduction

Reproduction takes place only by sexual means.

  • They are hermaphrodites (monoecious).
  • Fertilisation is external.
  • Development is indirect with a larval stage (cydippid larva).

Q1. What are Ctenophores commonly called, and where are they found?

A1. Ctenophores are commonly known as sea walnuts or comb jellies. They are found exclusively in marine environments.

Q2. What is the most distinctive feature of Ctenophores, and what is its function?

A2. The most distinctive feature is the presence of eight external rows of ciliated comb plates. The coordinated beating of the cilia on these plates helps the animal in locomotion (swimming).

Q3. What is bioluminescence, and why is it significant in Ctenophores?

A3. Bioluminescence is the ability of a living organism to produce and emit light. This property is well-marked in Ctenophores, making them glow, often spectacularly, in the dark marine environment.

Q4. How do Ctenophores reproduce?

A4. Ctenophores reproduce only sexually. They are hermaphrodites (possessing both male and female reproductive organs). Fertilisation is external (gametes released into the water), and development is indirect, involving a larval stage.

Q5. How do Ctenophores differ from Cnidarians (Coelenterates) in terms of specialized cells and reproduction?

A5. Key differences include:

  • Stinging Cells: Cnidarians have cnidoblasts (nematocysts) for prey capture and defense, while Ctenophores lack these and typically use sticky cells called colloblasts (on tentacles, if present).
  • Reproduction: Cnidarians show both asexual and sexual reproduction, often with alternation of generations (metagenesis). Ctenophores reproduce only sexually.