Cell surface proteoglycan that bears heparan sulfate (By similarity). Required for correct mitotic spindle orientation of the ABar blastomere division plane and this may be through modulation of astral microtubule array, and in association with the wnt-signaling proteins mig-5 and dsh-2 (PubMed:25344071). Involved in the migration of AQR and PQR neurons, which descend from the Q neuroblasts (PubMed:26022293). Promotes the axon guidance of D-type motor neurons (PubMed:24066155). Initially localizes to the ABar blastomere cell surface during interphase and prophase, and is internalized during metaphase and anaphase. Expressed from the one-cell stage of embryogenesis onwards. The cytoplasmic domain is required for correct mitotic spindle orientation and internalization of sdn-1. Disrupted mitotic spindle orientation of the ABar blastomere division axis, orientating parallel rather than orthogonally to the division axis of AB derived cells ABpr and ABal (PubMed:25344071). Reduced mig-5 accumulation at the cell contact sites between the ABar and C blastomere cells (PubMed:25344071). Irregular positioning of the AQR and PQR neurons in larva at the L4 stage (PubMed:26022293). Belongs to the syndecan proteoglycan family.