The prostomium bears eyes, two pairs of antennae and a pair of large retractile nuchal organs.
3.
It carries two ciliated nuchal organs between its prostomium and peristomium, the latter being similar in length to the adjacent segments.
4.
In the Phascolosomatidea, the tentacles are arranged in an arc around the nuchal organ, also located at the tip of the introvert.
5.
The head also includes a pair of antennae, tentacle-like palps, and a pair of pits lined with cilia, known as " nuchal organs ".
6.
Two organs, likely functioning as a unit for chemoreception are located near the anterior margin of the cerebral ganglion : the non-ciliated cerebral organ, which possesses bipolar sensory cells, and the nuchal organ, located posterior to the cerebral organ.
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