Complex sentence: Styliform and ventrally directed abdominal gills are developed on segment 1-7 and have a broader, more strongly sclerotized basal part and a slender and rather membranous distal part.
Split into simpler sentences: Styliform and ventrally directed abdominal gills are developed on abdominal segments 1-7. These gills are composed of a broader, more strongly sclerotized basal part and a slender and rather membranous distal part.