Four species of the genus Haplosyllis from Indonesia are herein described and illustrated. In Haplosyllis aciculata sp. nov. and Haplosyllis ingensicola sp. nov. the longest midbody cirri exceed body width and posterior parapodia have a single broad, strongly curved acicula, while in Haplosyllis tenhovei sp. nov. and Haplosyllis nicoleae sp. nov. cirri are shorter than body width, and the two or more aciculae are straight or curved. The available information on the ecology and host species is provided.
