Scanning electron micrograph of the dorsal side of a newly hatched European nightcrawler (Eisenia hortensis). Clearly depicted in this photo are the earthworm's first 5 segments, mouth (the half-moon or U-shaped space at the tip of the first segment), prostomium (the dome of tissue defining the interior portion of the U-shaped mouth), and the setea (the hair-like structures made out of chitin which found on the lateral and ventral sides starting with the 2nd segment). On the prostomium, many small circular structures called epidermal sensory organs are visible. 
Photo by Hannah G Watson, Andrew T Ashchi, Glen S Marrs, &amp; Cecil J Saunders of the Wake Forest University Department of Biology (<a rel="nofollow" class="external free" href="http://biology.wfu.edu/">http://biology.wfu.edu/</a>). CC BY 4.0.
<a href="//commons.wikimedia.org/wiki/User:Jakesaundersphd" title="User:Jakesaundersphd">Hannah G Watson, Andrew T Ashchi, Glen S Marrs, Cecil J Saunders</a>
CC BY 4.0
<span class="int-own-work" lang="en">Own work</span>