Question

Statocysts are sense organs of
a. Paramoecium
b. Ascaris
c. Medusa of Obelia
d. Taenia solium

Answer 1

Hint: The statocyst is a balanced sensory receptor. It is present in some aquatic invertebrates, including molluscs, bivalves, cnidarians, ctenophores, echinoderms, cephalopods, and crustaceans. The statocyst consists of a sac-like structure containing Craspedacusta and similar medusae, a mineralized mass (statolith) and numerous innervated sensory hairs (setae).

Complete answer:
Statocysts are structures that aid in orientation and balance during activities like swimming in medusae and are located around the margin.

Paramecium is a unicellular organism. It has a shape resembling the sole of a shoe.
The sense organs of Ascaris are the simple extensions supplied by nerves.

Medusa of Obelia is a saucer-shaped structure and possesses a large number of marginal tentacles and sense organs like statocysts, attached by the middle of the convex surface to the blastostyle. The polyp in Obelia asexually produces medusae. They help in maintaining the balance and coordination of Obelia.

Hence, the correct answer is option (C).

Additional information:
The ectoderm lining of the medusae has some sensory cells with thin sensory processes on which the otoliths produce a stimulus which is transmitted by nerves to muscles; the muscles coordinate the snake-like swimming movements of the medusa, and should the medusa become tilted, the muscles contract to right the position of medusa bell, thus, statocysts are balancing organs.

Note: A statocyst is a tiny, circular closed vesicle lined with ectoderm and filled with certain granules called otoliths which are present in lithocyte. This lining has sensory cells. These sensory cells can transmit signals from nerve to muscle of the medusa in Obelia. Statocyst helps to maintain equilibrium in the larval stage (medusa) of Obelia.