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Phylum Ctenophora: General characteristics, Locomotion, Digestion, Bioluminescence, Reproduction, Examples and Classification

Have you ever gone on a voyage? Have you ever seen glowing creatures in an ocean at night time like fireflies appear in the air? Don’t worry if you haven’t. We will be exploring details of such creatures which act as fireflies of oceans. These creatures are collectively grouped into a phylum called ‘Ctenophora’. Ctenophora has been derived from two words ‘ktene’ meaning comb and ‘phors’ meaning bearing. Ctenophores are also known as sea walnuts or comb jellies which bear rows of comb plates. They are bioluminescent and break the darkness of nights in the oceans. Let’s go into the depth of phylum Ctenophora.

Table of Contents:

General Characteristics of Phylum Ctenophora

Habitat

Ctenophores are exclusively marine.

Symmetry

Ctenophores have their bodies divisible into left and right halves through any plane passing through the centre of the body, hence, they are radially symmetrical.

radial symmetry in ctenophora

Level of organisation 

Ctenophores have cells organised into tissues, hence, said to have tissue level of body organisation.

Germ layer organisation

Ctenophores are diploblastic as their cells are arranged into two embryonic layers, outer ectoderm (epidermis) and inner endoderm (gastrodermis). An undifferentiated layer is sandwiched between them called mesoglea.

Locomotion in Ctenophores

Ctenophores possess eight rows of ciliated comb plates externally which has a significant role in locomotion. The cilia present in the comb plates help them in swimming.

ciliary comb plate ni pleurobrachia

Digestion in Ctenophores

Certain ctenophores have specialised adhesive cells called Colloblasts in the epidermis of their tentacles which help them in food capture. 

Digestion occurs by both intracellular and extracellular means in ctenophores. They possess a complete digestive system with a mouth and anal pores.

complete digestive system ni ctenophora

Bioluminescence in Ctenophores

The ability to emit light is known as bioluminescence. It is a characteristic feature of the ctenophores. The phenomenon of light emission is mediated by the activation of calcium-activated proteins named photoproteins which are present in specialised cells called photocytes. The photocytes are confined mostly in the underlying meridional canals of the eight comb rows. Thus the comb rows appear glowing in the dark. Now could you understand the trick behind their glowing ability?

bioluminescence ni ctenopana

Mode of Reproduction and Development of Ctenophores

Ctenophores are hermaphrodites, i.e., sexes are not separate. They exhibit sexual reproduction only. Fertilisation occurs externally characterised by the fusion of gametes in an external medium such as water.

Ctenophores undergo indirect development through intervening larval stages which then transform into adults. The larval stage is ciliated and spherical, named as cydippid larva.

Examples of Ctenophores

  • Pleurobrachia
  • Ctenoplana 

PleurobrachiaCtenoplana

Classification of Phylum Ctenophora

Phylum Ctenophora are classified into two classes based on the presence or absence of tentacles.

Class Tentaculata

Members of this class have tentacles. Examples: Pleurobrachia, Ctenoplana etc.

Fig: Pleurobrachia Fig: Ctenoplana

Class Nuda

Members of this class do not have tentacles. Examples: Beroe

Practice Problems of Phylum Ctenophora

Q1. Shelly, while travelling to Andaman by ship, suddenly spotted an amazing glow just like LEDs in the ocean. She was wondering about some non-living entity in the ocean. While minutely noticing them, she spotted their movements. It appeared to be like a building having strings of glowing LEDs during Diwali. Can you help Shelly find the correct phylum of the creature?

  • Porifera
  • Ctenophora
  • Chordata
  • Arthropoda

Solution: Members of phylum Ctenophora have eight rows of ciliated comb plates which appear glowing. This is due to their bioluminescent properties. As the creatures were glowing like strings of LEDs in buildings, they are likely to belong to phylum Ctenophora.

Hence, the correct option is b.

Q2. Coelenterates and ctenophores differ in:

  • Presence of comb plates in coelenterates which are absent in ctenophores
  • Presence of comb plates in ctenophores which are absent in coelenterates 
  • Intracellular digestion in ctenophores while extracellular digestion in coelenterates 
  • Both b and c

Solution: Ctenophores have eight ciliated rows of comb plates. This is a unique feature of ctenophores which the coelenterates lack. The photocytes are confined mostly in the underlying meridional canals of the eight comb rows. Thus the comb rows appear glowing in the dark. Hence, the correct option is b. 

Q3. Following are a list of few characters given:

Symmetry, level of organisation, number of germ layers, presence of comb plates, presence of anal pores.

How many above-mentioned characteristics are common between coelenterates and ctenophores?

  • 5
  • 4
  • 2
  • 3

Solution

Character

Coelenterates

Ctenophores

Symmetry

Radial 

Radial 

Level of organisation

Tissue level

Tissue level

Germ layers

Two

Two

Comb plates

Absent

Present

Anal pores

Absent

Present

Three characters are common between coelenterates and ctenophores. 

Hence, the correct option is d.

Q4. Lower phyla usually have an incomplete digestive system. Which of the following is an exception to this?

  • Coelenterata
  • Platyhelminthes
  • Ctenophora
  • Porifera

Solution: Members of lower phyla usually have an incomplete digestive system consisting of a single opening which serves as both the mouth and the anus. Although phylum Ctenophora comprises of certain lower invertebrates, the members possess a better developed digestive machinery comprising of both mouth and anal pores. 

Hence, the correct option is c.

FAQs of Phylum Ctenophora

Question1.- Define Bioluminescence.

Answer. Bioluminescence refers to the phenomenon of production and emission of light. It occurs due to an underlying chemical reaction in a living organism where chemical energy gets converted into light energy.

Question2.- Enlist two unique features of members of phylum Ctenophora.

Answer. Two unique features of ctenophores are as follows:

  • Presence of comb plates for swimming.
  • Presence of colloblasts for capture of prey.

Question3.- Are ctenophores the same as jelly fishes? 

Answer. No, ctenophores and jelly fishes are not the same. Ctenophores belong to a separate phylum, Ctenophora while jelly fishes belong to the phylum, Coelenterata.

Question4.- Mention the other names of Ctenophores.

Answer. Various common names of Ctenophores include comb jellies, sea walnuts etc.

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