Question

Which of the following shows radial symmetry?
(a) Porifera and coelenterata
(b) Coelenterata and Echinodermata
(c) Coelenterata and Platyhelminthes
(d) Arthropoda and mollusca

Answer 1

Hint: They are mostly marine animals. They have the arrangement of body parts in which an organism can be divided into two equal halves from the central axis.

Complete Step by Step Answer:
The arrangement of parts in an organ or organism such that cutting down the center of the structure in any direction gives two halves that are mirror images of each other. All animals belonging to the Cnidaria (e.g. jellyfish) and Echinodermata (e.g. starfish) are radially symmetrical. And generally sessile (in their adult form).

Additional information:
General Characteristics of Coelenterata are:
- They are aquatic (marine) .
- They are multicellular.
- Respiratory, circulatory, and excretory organs are absent.
- Asexual reproduction by budding.
General Characteristics of Echinodermata are:
- They are simple animals that may be star-like, spherical, or elongated.
- Their bodies are triploblastic, unsegmented, and radially symmetrical.
- Their body lacks a head but has oral and abdominal surfaces.
- Excretory organs absent.
General Characteristics of Porifera are:
- Simplest multicellular, diploblastic animals
- Asymmetrical symmetrical.
- They do asexual reproduction.
General Characteristics of Arthropods are:
- Triploblastic, bilaterally symmetrical, and metamerically segmented animals.
- The Alimentary canal is complete.
- Sexes are usually separate.
General Characteristics of Platyhelminthes are:
- They are bilaterally symmetrical.
- It is triploblastic and has three germ layers.  
- They are acoelomates.  
General Characteristics of mollusca are:
- They are bilaterally symmetric.  
- They are triploblastic.   
So, the correct answer is option Coelenterata and Echinodermata’.

Note: Many sea anemones and some corals within the Coelenterata have bilateral symmetry defined by a single structure. Radial symmetry is unusually appropriate for sessile animals like the sea anemone, floating animals like jellyfish, and slow- moving organisms like starfish. Though bilateral symmetry benefits locomotion by generating a streamlined body.