Question

Sensory structures in Ascaris are
A. Phasmids
B. Amphids
C. Papillae
D. All of the above

Answer 1

Hint: Ascaris is the common roundworm that can be seen in our surroundings. It belongs to the phylum Aschelminthes which includes all roundworms. They are also called Nemathelminthes.

Complete answer: Aschelminthes are pseudocoelomate organisms with ‘tube within a tube’ type of a body plan. They are bilaterally symmetrical in nature as they can be divided into two equal halves only in one plane. The body of roundworms is unsegmented in nature. Development of these organisms is indirect. Ascaris has several organs for sensory functions, such as papillae, amphids and phasmids are examples for these structures. Body of roundworms is covered by a thick and resistant layer made up of cuticles. It is secreted by the underlying epidermis. Sensory structures are actually the invaginations seen in the cuticular layer. The epidermal layer of roundworms is a multinucleate mass of protoplasm without intervening cell membranes. Such a protoplasmic mass is known as syncytium. Roundworms have a straight and complete alimentary canal with mouth and anus. Circulatory system and respiratory system are absent in these animals. The nervous system of roundworms is of a simple type with four major nerves that run throughout the body. The brain of these animals is a primitive type. It processes the sensory input given by the sensory structures and enables the sensory perception for these animals. Most of the sensory input will be chemical ones from the surroundings of these animals.
Roundworms are animals showing sexual dimorphism. Hence the correct option is D.

Note: Hermaphrodites are also called monoecious as the sexes are not separate in these individuals. They are also called bisexual animals. If separate sexes are seen in certain animals, they are called dioecious or unisexual animals. So, roundworms are unisexual in nature.