Question

Read the statements regarding echinoderms and choose the correct option
(i). All are marine with organ system level organization
(ii). Adults are bilaterally symmetrical
(iii). They are dioecious
(iv). Fertilization is internal and indirect development is observed
(v). Triploblastic and acoelomate animals
A. (i) and (ii) are correct
B. (v) alone is correct
C. (i), (iii), and (v) are correct
D. (i) and (v) are correct
E. (i) and (ii) are correct

Answer 1

Echinoderms are characterized by radial symmetry in adults. Sea urchins, starfishes, sand dollars, etc. are echinoderms. They are found at every depth of the ocean but mostly at benthic zones. Most of the echinoderms are able to regenerate and have an asexual mode of reproduction. They are a major source of limestone.

Complete answer:
The echinoderms are a group of 7000 known marine living species. Thus, all of the echinoderms are marine and most are found in the benthic (lowest) region. They are found at every depth of the ocean, even the deep sea deserts are inhabited by echinoderms. Starfishes, sea urchins, sea cucumbers, sand dollars, etc. are examples of echinoderms.
The body of echinoderms is uniquely spherical. They have an elongated or star-shaped body with the organ-level organization as stated in statement (i). They are triploblastic organisms having a true coelom. They lack a segmented body and head. Their body is usually covered with a calcareous endoskeleton. Hence, statement (i) is correct.
Echinoderms are not bilaterally symmetrical but they are thought to be evolved from bilateral symmetry possessing organisms. Echinoderms have radial symmetry. They exhibit bilateral symmetry usually in their larval stage but adult echinoderms have radial symmetry. So, statement (ii) is incorrect.
Echinoderms have male and female reproductive organs in separate individuals and thus they are dioecious. Only a few of them are true hermaphrodites and can self-fertilize. So, statement (iii) is correct.
Fertilization in echinoderms is external as eggs and sperms are typically released in the water where fusion occurs. The development of zygotes is indirect as they pass through a planktonic stage which is a free-living and feeding larval stage. So, statement (iv) is incorrect.
Echinoderms are triploblastic organisms as their body is derived from three different layers. The outermost layer is of calcareous substances and bears calcareous spikes. Echinoderms lack a specialized body cavity that is located between the intestinal canal and body wall called coelom. Hence, they are acoelomates. So, statement (v) is correct.
Hence, from the above discussion, we can conclude that option C is the right answer.

Note: The ossified skeletons of echinoderms serve as the major source of limestone. They were used extensively to study regeneration in the 19th and 20th centuries. Sea urchins are used as model organisms in the field of developmental biology. Other uses of echinoderms include their use as animal feed.