Question

Give two examples of phylum Ctenophora.

Answer 1

The phylum Ctenophora includes marine, planktonic and biradially symmetrical organisms with an oral-aboral axis. These animals are acoelomates and have tissue level of organization. There are about 100 living species of Ctenophora.

Complete answer:
- Ctenophora are diploblastic animals but mesoglea is with many amoebocytes and smooth muscle fibres. It is developed from mesoderm so it is called mesoblast.
- Their locomotion is by ciliary movements of 8 vertically arranged comb plates or ctenes, so are commonly called comb jellies or sea walnuts.
- They generally have one pair of long, solid and retractile tentacles that have special adhesive cells called colloblasts or lasso cells but do not have cnidoblasts so it is called Acnidaria.
- These animals have a complete alimentary canal and are carnivorous. The digestion is partly intracellular and partly intercellular.
- The respiration and excretion occurs through the body surface and are ammonotelic in nature.
- They have a diffused nervous system. The peculiar sense organ of ctenophores is statocyst which lies in a pit at the abdominal pole and helps in equilibrium.
- The asexual reproduction is absent in these animals.
- They are bisexual or hermaphroditic in nature that shows external fertilization. The development includes a ciliated cydippid larva.
- The examples of the animals of this phylum are Ctenoplana, Hormiphora, Pleurobrachia (sea-gooseberry), Cestum (Venus’s girdle), etc.

Note: Bioluminescence is a well-marked feature of animals of this phylum. The phylum Ctenophora is also called Acnidaria as these lack cnidoblasts. Mesoglea of ctenophores is of collenchymal nature i.e.it has many cells.