Diagnostic characters
Shell with moderately high spire with pointed apex; whorls swollen with strap-shaped spiral ridges. each often with a small central groove. Aperture oval, outer lip arising nearly at right angles to last whorl and everted at base of columella to form a short spout. White, grey, yellow or red. the spiral grooves often dark, but never with a reticulated pattern. Penis rather flat with short tip and up to twelve glands close to tip. Oviparous, hence female duct glandular.
Other characters
The shell has six whorls. There are 10-21 ridges on the last whorl, 3-7 on the penult, 3-4 on the most apical; the intervening grooves are narrow. Up to 20mm high. 18mm broad: last whorl occupies 75-90% of shell height, aperture two thirds to three quarters.
The animal is like L. littorea (but has only longitudinal stripes on its tentacles. The flesh is yellowish; the penis is white, and from its base a white streak passes diagonally backwards on the floor of the mantle cavity.
L. nigrolineata is found amongst weeds and stones on rocky shores, at levels related to the degree of exposure but commonly at about M.T.L., creeping actively after both emersion and immersion (Petpiroon & Morgan, 1983). It eats weeds, microphytes and detritus (Sacchi. Testard & Voltalina, 1977). The animals have been recorded from localities on the western sides of the British Isles between Scilly and Lewis as well as on the northern shores of the North Sea.
These winkles breed throughout the year, with a summer maximum (Sacchi, 1975), laying eggs in capsules embedded in jelly masses which are fastened to the underside of the stones amongst which they live. The eggs are pink and the capsules in which they lie are angular in outline. The young hatch as juvenile snails with shells (1.5 mm high in 4-7 weeks (North Wales) and are estimated to take 6-9 months to grow to 4 mm. with a winter pause in growth (Hughes, 1980). and probably a further year to reach maturity