Fields of View of the Eyes Of Primitive Jumping Spiders

Abstract

ABSTRACT Most spiders have eight simple eyes, of which one forward-pointing pair (the principal eyes) has a different structure from the other three pairs (the secondary eyes). The principal eyes are often movable, whereas the secondary eyes are fixed. In most jumping spiders (Salticidae) two of the secondary eyes, the postero-median pair, are so reduced that they seem to be vestigial, and their fields of view overlap those of the other secondary eyes (the antero-and postero-laterals) (Homann, 1928; Land, 1969a; Eakin & Brandenburger, 1971). However, in certain supposedly primitive Salticid sub-families the postero-median eyes are comparable in size with the other secondary eyes, and would appear to play a more equal part in the function of the secondary eye system, which is the detection of movement (Land, 1972). The origins of the Salticidae are something of a mystery, and it is therefore of considerable interest to see whether the fields of view of the eyes of these primitive sub-families give any clue that might indicate to which of the other spider families the Salticidae might be linked. The form of the fields of view appears to be a conservative feature in spider evolution (Land, 1985), just as does the layout of the eyes themselves. The anatomy and ultrastructure of these eyes have been described before (Blest, 1983, 1984, 1985; Blest & Sigmund, 1984) and the systematic position of the sub-family considered here, the Spartaeinae, is discussed by Wanless (1984).