Elysia Anatomy

Elysia can be thought of as a pancake, or perhaps a crepe, with a head sticking out one end.  When the parapodia are fully opened, as shown in the dorsal view of E. chlorotica below, the animal presents a large, dorsoventrally flattened surface area.  The photograph also highlights circulatory system, comprising the heart and branched dorsal vessel.  Rhinophores, organs of smell and taste, can be tapered like those of E. chlorotica, or scoll-like, as shown for E. clarki.



The locations of the foot and parapodia (singular: parapodium) can be seen in a ventral view of E. clarki, below.



With the parapodia folded up, Elysia looks more like a typical slug.



The tiny eyes (arrow) are probably too simple to form images.  Note also the scrolled rhinophores.



With a little magnification, the stolen chloroplasts can be seen through the skin as tiny green dots.




 Why do people scold me for calling Elysia a nudibranch?  There are a couple of ways to answer this.  The simplest is to simply look at the slugs.  Nudibranch literally means “naked gills,” which are proudly displayed on their dorsal surface, as shown for Tambja (below right).  The large surface area of Elysia (left) allows it to rely on diffusion across its body wall for gas exchange, eliminating the need for gills.

Nudibranch (right) vs Elysia (left)

Nudibranch (right) vs Elysia (left)


  1. Reply
    Lyric Nunley May 22, 2017

    Do these sea slugs have a skeletal system?

    • Reply
      Dave May 23, 2017

      No skeleton. They are as squishy as they get.

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