The setal armature of Eurydice pulchra Leach is described using an ordinary optical microscope. On the basis of size, setae are divided into macrotrichs and microtrichs. Macrotrichs are further classified according to structural similarities into four groups. Only two types of microtrichs have been recognized. The distribution of the different setae on both adults and juveniles is described and where possible an attempt is made to relate morphology and distribution to function.
The setal armature of E. pulchra has been divided into macrotrichs, varying in length from 0·025 to 0·4 mm, and microtrichs varying in length from 2 to 10 μm. The macrotrichs have been classified into groups based on structural similarities and 17 distinct types have been recognized. Each differ in length, degree of chitinization and modification of the shaft wall. The distribution of the macrotrichs has been described and particular types have been shown to occur in distinct positions on the body. Many of the macrotrichs are peculiar to one position on the body.
Two types of microtrichs have been described, a single type approximately 10 μm in length and a smaller type 2 μm in length. The latter occurs in short crescentic rows principally on the pleopods and oostegites. All setal types occurring in the adult have been shown to be present in the newly emerged juvenile although the number developed is very much less. Similar setal types are present in males and females. An attempt has been made to relate the morphology and distribution of both macrotrichs and microtrichs to possible functions.