1	Aciculae straight, with a bulbous distal swelling. Mid body parapodia with simple chaetae by loss of blades and shaft enlargement	Sphaerosyllis bulbosa Southern, 1914 (1)
–	Aciculae distally bent at an angle. Without enlarged chaetae	2
2	Antennae, tentacular and dorsal cirri minute, bulbous. Blades of mid body and posterior compound chaetae with smooth margins, with a long subdistal spine	Sphaerosyllis parabulbosa San Martín & López, 2002 (1)
–	Antennae, tentacular and dorsal cirri not so small, with longer tips. Blades otherwise	3
3	Without parapodial glands	4
–	With parapodial glands from chaetiger 4	5
4	Proventriculus rectangular. Compound chaetae of posterior parapodia with short, hooked, smooth blades	Sphaerosyllis pirifera Claparède, 1868 (1)
–	Proventriculus almost square. Compound chaetae with blades elongated throughout body	Shaerosyllis sp.
5	Parapodial glands with granular material	Sphaerosyllis glandulata Perkins, 1981(1) (*)
–	Parapodial glands with fibrillar material (rods)	6
6	Blades of compound chaetae with distinct dorsoventral gradation in length, especially on anterior parapodia	Sphaerosyllis hystrix Claparède, 1863 (1)
–	Blades of compound chaetae with, at most, very slight dorsoventral gradation in length; all blades short, those of dorsal compound chaetae with long spines on margin	Sphaerosyllis taylori Perkins, 1981 (1) (*)