External Morphology
Symmetry and shape
Adults of
the blue sea star typically have five armsand are pentamerous radial
symmetrical. The larvae, on the other hand, are bilaterally symmetrical
(Ruppert, Fox & Barnes 2004). The arms of Linckia laevigata are
rounded and are barely tapering. Arms are not distinct from the central
disc and at the end of each arm, sensory tube feet (tentacle-like) and a
eyespot can be found.
Aboral Side
The
aboral side is generally facing upward. Anus is not easily
recognizable, yet an asymmetrical spot named madreporite is always
distinct on the aborsal surface.
Oral Surface
The mouth is located in the center of the oral surface. A wide furrow, named the ambulacrum (or ambulacral groove), is found under each arm. Short, yellowish tubular projections called tube feet are found within the ambulacral groove. Below is a video of L. laevigata tube feet protruding from the ambulacrum groove underneath the arm.
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