Final answer:
Brittle stars are known for being the largest class with the most species in Echinodermata but exhibit the least morphological diversity compared to other echinoderms like sea stars.
Step-by-step explanation:
Brittle stars, which belong to the class Ophiuroidea, are known as the largest class with the largest number of species in the phylum Echinodermata. While they exhibit great diversity in species, they show the least amount of morphological diversity, especially when compared to other echinoderms like sea stars (class Asteroidea), which have a variety of shapes, colors, and sizes. Brittle stars differentiate from their relatives because they have long, thin arms that starkly contrast with the central disk and do not contain organs. In addition, while sea stars use their tube feet for locomotion, brittle stars do not use their water vascular system for this purpose but rather move by lashing their arms or wrapping them around objects. This limited morphological diversity is contrasted with their large population and extensive variety in species.