Question

Biradial symmetry and lack of cnidoblasts are characteristics of
A. Hydra and Starfish
B. Starfish and Sea anemone
C. Ctenoplana/Ctenophora and Beroe
D. Aurelia and Paramoecium

Answer 1

Hint: Animals can be classified on the basis of symmetry and the animals can be differentiated on the axis (imaginary straight line passing through the centre of body) or plane (flat surface which divides the body into two equal halves).

Complete answer:
Biradial symmetry and lack of cnidoblasts are the characteristics of Ctenoplana/Ctenophora and Beroe.
Biradial symmetry is a combination of radial and bilateral symmetry. Biradial symmetry is found in organisms which shows morphological features of both bilateral and radial symmetry. Biradial organisms can only be cut along the two planes (longitudinal and transverse plane) equally. Ctenophores show the biradial symmetry.
Cnidoblasts are the oval shaped cells present on the tentacles and the body. These specialised cells contain a nucleus and a stinging capsule called nematocyst. Nematocyst is filled with a poisonous fluid called hypnotoxin. This poison is injected by the help of a thread tube (piercing needle) in the prey or predator. Phylum ctenophora lacks the cnidoblasts. The cnidoblasts are the characteristics of phylum Cnidaria/Coelenterata.
Hydra, Sea anemone and Aurelia are coelenterates which bear cnidoblasts.
Beroe is also known as mellon jellyfish and falls under the phylum ctenophora.
Starfish belongs to phylum echinodermata.
Paramoecium belongs to phylum ciliophora.

So the correct answer is option C.

Note: Tentacles may be present or absent on ctenophores. At present, the number of tentacles is two. They are solid and possess adhesive cells called colloblasts (lasso cells). Bioluminescence is the special characteristic of ctenophora. It is the production and emission of light by an organism which glows in the dark places.