The Fine Structure of the Compound Eyes of Shallow-Water Asellotes, Jaera albifrons Leach and Asellus aquaticus L. (Crustacea: Isopoda.

Both species have small sessile compound eyes. The dioptric apparatus of J. albifrons consists of a biconvex lens and a pyriform crystalline cone, the latter formed by two principal and two accessory cone cells. A. aquaticus has a reduced lens and a round cone formed by two to four principal cone cells with two to no accessory cone cells. Distal pigment cells and pigmented retinular cells lie between the ommatidia in J. albifrons. A. aquaticus has only the pigmented retinular cells. Both species have a fused, continuous (unbanded) rhabdom formed by eight retinular cells (R1–8), one of which (R8) is situated distally. The retinular cells R1–7 form, in J. albifrons, a cylinder-shaped middle portion with three microvillar directions (60° apart) and a proximal star-shaped portion. The entire rhabdom of A. aquaticus is star-shaped. Distal pigment-ceil processes and basal cells form the fenestrated membrane in J. albifrons and ‘eye-cup cells’ in A. aquaticus. [ABSTRACT FROM AUTHOR]