Question

In which class of echinodermata, the stalk is found for attachment with substratum?
a. Asteroidea
b. Echinoidea
c. Ophiuroidea
d. Crinoidea

Answer 1

The phylum echinodermata are the invertebrates, which have spiny skin, pentaradial symmetry the adult echinoderms are radially symmetry whereas larvae are the bilateral symmetry, simple nervous system and vascular system.

Complete answer:
Classes of echinoderms: it is divided into five different classes: Ophiuroidea (sea star), echinoidea (sand dollars and sea urchins), asteroidea (sea stars), crinoidea (feather stars and sea lilies) and holothuroidea (sea cucumbers).

Some of the characteristics feature of each class:
• The class Ophiuroidea includes the brittle star; they have thin, long arms that are sharply fixed to the central disk. Locomotion of the brittle star is done by lashing out their arms or also by wrapping the arms around the objects and then pulling themselves forward. Mostly these classes are detritivores and scavengers.
• Echinoidea includes sea urchins and sand dollars. They do not have arms rather they have flattened or hemispherical tube feet that help in slow movements.
• The class asteroidea are the best-known members of the echinoderms. Sea stars belong to this class. The members belonging to this family are different in shapes, sizes, colour. They have thick arms which extend from the central disk where organs penetrate the arms. They use their tube feet for movement and grasping the prey.
• The class crinoidea have sea lilies and feather stars which are suspension feeders. These are marine animals. The sea lilies are crinoids, when they are in their adult form, they are attached to the sea bottom by the stalk. They usually have five or more than five arms. They have a stem which is attached to them to the substrate by the large and terminal disc or by branching, irregular radicular at the bottom of the stem. Although the feather stars refer to unstalked form.
• Holothuroidea has an oral-aboral axis and five rows of tube feet. These animals lie horizontally instead of standing vertically and only these classes demonstrate functional bilateral symmetry as adults.

Hence, the correct answer is option (D).

Note: Some general features of echinoderms are:
• They reproduced asexually by the process of regeneration.
• They have two sexes male and female which releases their gametes into the water. Inside the water, the sperm will fertilize the egg.
• The echinoderms are Coelomate and triploblastic animals.
• The most important and special features of echinoderm are the water vascular system. This system helps in the locomotion, respiration, capturing of food, and transportation of food.