Embedded in the brain of
Armandia brevis are three prostomial ocelli, each composed of two cells. The pigment cell, surrounds a photoreceptor, and forms a pigmented cup and a transparent unpigmented diaphragm. The terminal part of the photoreceptor lies within a receptoral cavity. Its surface is elaborated into folds containing tubular infoldings.
The brain of Armandia contains, in addition to ocelli, photoreceptor-like cells partially enclosed by unpigmented epithelioid cells.
The prostomial ocelli of Armandia closely resemble the ocelli in the dorsal nerve cord of the protochordate Amphioxus (Eakin and Westfall, 1962). It is suggested that the similarity is the result of evolutionary convergence. The prostomial ocelli of Armandia and nereid polychaetes (Eakin and Westfall, 1964) have similarities suggesting homology.
The authors wish to thank Drs. Patricia L. Dudley and Richard M. Eakin for critically reading the manuscript. This investigation was supported, in part, by a Public Health Services fellowship, number 5-Fl-GM-20, 637, from the National Institute of General Medical Science.