AN ULTRASTRUCTURAL INVESTIGATION OF HRABEIELLA PIZL AND CHALUPSKY, 1984 (ANNELIDA) .1. CHAETAE AND BODY-WALL ORGANIZATION

Specimens of Hrabeiella sp., collected for the first time in Italy (Tu scany), were investigated by transmission and scanning electron micros copy, Chaetae conform with previous descriptions in light microscopy, but appear considerably different in electron microscopy, as they show an unusual brush-like pattern. The first TEM analysis of the body wal l layers was undertaken. The cuticle ultrastructure is similar to that found generally in very small-sized annelids, in that a coarse collag enous grid is absent, but it is peculiar for the paucity of ascending microvilli. Three different types of secretory cells are distinguishab le in most of the 12 epidermal glandular blocks occurring around the b ody circumference. Such blocks regularly alternate with as many muscle fields, each containing four longitudinal fibres. A subepidermal laye r of circular muscles is present. The somatopleure is cellular and com plete.