Parasphaerosyllis Monro, 1937 is a syllid genus, currently composed of four species: P. indica Monro, 1937 from the Arabian Sea, P. uschakovi (Chlebovitsch, 1959) from the Kurile Islands, P. ezoensis Imajima & Hartman, 1964 from Japan and P. malimalii Capa, San Martín & López, 2001 from the Pacific coast of Panama. The distribution of P. indica is circum-tropical to temperate waters, but the presence of species complexes has been suggested. In order to clarify the distribution of P. indica in many areas of the world, a re-description, based on examination of the type material, is required as a first step to a better understanding of its diagnostic features.

Parasphaerosyllis indica is re-described, based on holotype examination, a new species is established from the Gulf of California and Parasphaerosyllis malimalii is reported for the first time since its description in 2001. Parasphaerosyllis irregulata sp. nov. is distinguished from its congeners by the following features: 1) Palps are free at their base; 2) Two types of dorsal cirri are present: spherical to bulbous and moniliform cirri; 3) Both types of cirri are distributed irregularly. A spherical/bulbous and moniliform cirrus may appear together within the same segment (asymmetrical segment) or only a spherical/bulbous cirrus may appear in several consecutive segments (not alternating as occurs in congeners); 4) The spherical/bulbous cirri may have distal knobs with 1–3 terminal articles; and 5) Bidentate falcigers with short, sub-triangular blades with a proximal tooth slightly larger that the distal one. A taxonomic key to species of Parasphaerosyllis species is included.