I don't recognize this from any of the games. It looks vaguely like a rachni, but I strongly doubt it is. Is it ever confirmed that it is a rachni, or is there another species I'm not thinking of that more closely resembles it?
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It's a Hanar on its back in the Fornax lounge. Note the coloration and similar shapes.
The Hanar are a species resembling Earth's jellyfish and are one of the few non-bipedal Citadel races. Hanar are known for their intense politeness when speaking, and their strong religious beliefs regarding the Protheans, whom they refer to as "the Enkindlers".