The term epiathroid (Ancient Greek epi-, "above" + -athroid, "gathered together") is used to describe the arrangement of ganglia in the nervous system of molluscs. In the epiathroid state, the pleural ganglia of the "chest" and the pedal ganglia of the "feet" lie close to the cerebral ganglia of the "head" forming a neural cluster which begins to approximate a brain. It is a condition characteristic of the Mesogastropoda and Neogastropoda, and is the obverse of the more-primitive hypoathroid condition in which the pleural and pedal ganglia lie close together under the animal's gut and communicate with the cerebral ganglia via long connectives. The Archaeogastropoda clade is described as "hypoathroid", and is the clade closest to the original hypothetical ancestral mollusc (sometimes called an "archimollusc" or a H.A.M.).
- Chase, Ronald (2002). Behavior and Its Neural Control in Gastropod Molluscs. Oxford University. p. 22. ISBN 9780195354485.
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