Question

Which is not the characteristic of echinoderms?
A. Endodermal skeletal system
B. Bilateral symmetry
C. Free floating larva
D. Water vascular system

Answer 1

Hint: Echinoderms are members of the phylum Echinodermata and are exclusively marine aquatic animals. They are found at ocean depth ranging from intertidal zones to the abyssal zone. The important organisms are starfish, sea urchins , sea cucumbers and sea lilies which are also known as stone lilies.

Complete answer:
The echinoderms are radially symmetrical during the adult stages but are evolved from the animals with radial symmetry. Although the adults are five sided or radial symmetry, the larvae are bilaterally symmetrical. The bodies of the adults are arranged in five parts around a central axis. This characteristic is a type of adaptation to the sessile and sedentary existence.
The echinoderms are supposed to develop from the members of the Bilateria and are known to exhibit bilateral symmetry in their larval stages. The larvae of echinoderm are free swimming organisms that exhibit bilateral symmetry.
The echinoderms consist of a mesodermal skeleton. The mesodermal skeleton is composed of calcareous plates which are known as the ossicles. The calcareous plates are made up of a crystal of calcite. These ossicles or plates are fused together in some species of echinoderms such as sea urchins and may also articulate with each other as in other types of echinoderms as in sea stars. The ossicles are supported by a tough epidermis and may be flat or bear spine-like projections.
The echinoderms are aquatic organisms and possess a unique water vascular system. The water vascular system is also known as the ambulacral system. It is a network of fluid filled canals which is derived from the body cavity or the coelom. It is important and helps in the gaseous exchange, feeding, sensory reception as well as locomotion. The water vascular system opens to the exterior by the madreporite which is a net like structure. It opens to the aboral or upper side of the organism. The madreporites are connected to the stone canal and further the stone canal connects to the ring canal. The ring canal encircles the mouth or oesophagus and it extends along the arms. From the radial canal, short lateral canal branches off and ends into the ampulla present in the feet. The ampulla opens to the outside through a pore and is known as the podium or the tube feet.

Therefore, the option is option A.

Note:
The echinoderms are aquatic organisms and possess a mesodermal skeleton system. The skeletal system is made up of calcareous plates. The adults represent the radial symmetry in the body structure while in the larvas the body shows bilateral symmetry. The water vascular system represents an important system as it helps in different functions of the echinoderms.