Key facts

Length usually 1–1.5 cm, occasionally 3 cm, width 1–2 mm. Head rounded but not narrow and not demarcated from body. Four dark eyes arranged in a square, body stout and cylindrical. Colour is variable in shades of grey or olive green, and characteristically speckled with yellow or goldshimmering pigment grains sometimes diffusely distributed over body but sometimes arranged to a longitudinal band rendering the impression of a stripe.