Question

Which of the following animals does not belong to phylum Echinodermata?
i. Starfish
ii. Eocrinoidea
iii. Sea cucumber
iv. Chiton

Answer 1

Hint: A phylum is a classification or taxonomic rank that falls between kingdom and class. While the International Code of Nomenclature for algae, fungi, and plants recognises the terms as equivalent, the term division has traditionally been used in botany instead of the phylum.

Complete answer:
The phylum Echinodermata is made up entirely of aquatic animals. Echinoderms can be present in both deep water and shallow intertidal zones.
i) Starfish : Starfish, also referred to as sea stars, are echinoderms with a star-shaped body that belongs to the Asteroidea class. Starfish belong to the phylum Echinodermata. Hence this is not the correct answer.
ii) Eocrinoidea : The Crinoidea are echinoderms that lived between the Early Cambrian and Late Silurian periods and are now extinct. They were the most common echinoderms during the Cambrian period and are the oldest known group of stalked, arm-bearing echinoderms. Eocrinoidea belongs to the phylum Echinodermata. Hence this is not the correct answer.
iii) Sea cucumber : Sea cucumbers are echinoderms belonging to the Holothuroidea family of echinoderms. They have a leathery covering and an elongated body with a single branched gonad. Sea cucumbers belong to the phylum Echinodermata. Hence this is not the correct answer.
iv) Chiton : Chitons are marine molluscs that belong to the Polyplacophora class, which used to be classified as Amphineura. Chiton belongs to the phylum Mollusca, and it does not belong to the phylum Echinodermata. Hence this is the correct answer. Chiton is an animal that does not belong to the phylum Echinodermata.

Therefore, the correct option is iv) Chiton.

Note:
The fact that the phylum Echinodermata is entirely made up of marine organisms is an interesting aspect. Gaseous exchange, food circulation, and waste elimination are all handled by echinoderms' water vascular system.