Animal with a delicate, 7-16 mm, long body. The dorsal surface is brown to brownish-yellow, often with white or dark spots due to the underlying ovaries. A pair of nuchal tentacles is present, each scattered with five to eight eyes, but as many as 11 eyes is possible; the cerebral eyes are arranged in two elongate clusters, each with 10-16 eyes (S. maculata-eyes). The pharynx is mainly present in the second quarter of the body length, with three or four pairs of shallow folds.
The genital pores are separated, close behind the pharynx. The vasa deferentia open separately into a fusiform seminal vesicle; the muscular prostatic organ is also fusiform; the male antrum is rather wide, containing a thick unarmed penis-papilla. The vagina forms an anteriorly directed loop; shell-chamber is long; the [t]Lang's vesicle[/t] is small and globular (S. maculata-detail).
This species has a direct life cycle. Spawns in Augustus and September.
Under stones in tidal zone, among weeds in rock pools, in Laminaria holdfasts, on colonies of tunicate and on shell and gravel up to depths of 40 m.
Ranges from Scandinavia to western Mediterranean. Various British and Irish localities.