Most Modern Echinoderms Assume a Mouth-Down Feeding and Locomotion Posture

question 26

Multiple Choice

Most modern echinoderms assume a mouth-down feeding and locomotion posture.Members of the class Crinoidea are an exception.They are attached,mouth-up,and feed using tube feet to trap food from the water column.Recent molecular analyses show the Crinoidea to be basal to other extant classes.Which of the following help to explain these observations?

• A)Feeding and locomotion posture is not a phylogenetically significant character as all fossil echinoderms assumed a mouth-down posture.
• B)The mouth-up posture must be an ancestral character.The mouth-down posture evolved secondarily.
• C)The molecular analyses must be in error.The mouth-up posture is phylogenetically significant and must have been derived secondarily.
• D)There is no reasonable explanation for these observations at this time.

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