OESOPHAGUS STOMACH
ECHINODERMS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Class Holothuroidea, sea cucumbers
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Class Asteroidea, Starfish
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Class Echinodea, sea urchins
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Class Crinoidea, sea lilies and feather stars
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Detailed explanation-1: -The first hypothesis suggests that crinoids evolved from the blastozoan eocrinoids and cystoids. Eocrinoids were from the Early Cambrian and were the earliest echinoderms with a stalk, and arms. The group Gogiida is often referenced and is recognized by its vase-shaped body.
Detailed explanation-2: -The oldest known echinoderm may be the Vendian fossil Arkarua, found in southern Australia. It was soft-bodied but may have had some sort of unmineralized plates on its body. The Vendian fossil Tribrachidium may have been related to the echinoderms, but this is still debated.
Detailed explanation-3: -The Stelleroids. Perhaps the most common echinoderm is the sea star. Echinoids. The class Echinoidea includes the sea urchins, heart urchins, cake urchins and familiar sand dollars. Holothuroids. The class Holothuroidea is composed of creatures called sea cucumbers.