Two microvillar organs, new to Crustacea, in the Mystacocarida.

The mystacocarid crustacean Derocheilocaris typica has two microvillar organs, one new, the other previously unappreciated in crustacean literature. The first is situated on the head-shield and consists of three pairs of cells: one with microvilli and a ballooned nucleus; one smaller and without special features; the third large and investing the other two and extending down to the foregut. We call this new organ the "cephalic microvillar organ" and discuss the value of the concept "dorsal organ", to which it might have been included. The second organ consists of about 21 cells that cover the proximal part of the dorsal surface of the labrum. The cells are alike, being characterized by an apical field of microvilli and a large residual body. This organ is here called the "labral microvillar organ". Both organs are neither sensory nor secretory and do not qualify for membership in any of the other recognized organ systems. We are unable to deduce their Dero-cheilocaris functions.