Littorina obtusata

Littorina obtusata, Flat Periwinkles, are sea snails and sea slugs. They grow to 1.5 cm in height.^[2] They can be brown, yellow, olive green, and black.^[3] They are mostly found in the colors of brown, reddish brown, or yellow, with few being red or white because of the abundance of brown seaweed.^[4] Littorina obtusata get the name, Flat Periwinkle, because they have a flattened spire and a large tear-dropped shaped aperture. The last whorl of the shell makes up 90% of their height.^[5] The maximum recorded shell length is 13.5 mm.^[6] This species is mainly littoral, but also has gill respiration.^[7] This means that they can survive both in water, and extended amounts of time on land.

This marine species occurs wherever brown seaweeds grow. It is widely distributed: the Baltic Sea, in European waters from Norway down to Southern Spain, in the Mediterranean Sea, in the Northeast Atlantic Ocean along the Gulf of Maine.

The flat periwinkle is not highly studied, so not much is known about them. Despite this, there have been recent developments in research on them, such as the following: It has been suspected that the L. Obtusata and L. Falbalis were the same species, then diverged into two species during their evolution. Scientists were still debating when this divergence occurred.^[8] L. Obtusata tends to be bigger and live longer than L. Falbalis. Research suggests that L. Obtusata and L. Falbalis are starting to hybridize despite the strong differences in their genetics. The name of the hybridized species is L. Saxatilis, but there is little information and research on it.^[9]

This species can be found in the littoral and sublittoral zone on rocky shores and piers, usually on brown algae of the genus Fucus. Minimum recorded depth is 0 m.^[6] Maximum recorded depth is 110 m.^[6] The habitat may define its color. On sheltered shores it has a lighter and uniform color (yellow, brown, orange or olive green). On exposed shores its color is darker and chequered. They are tolerant of low salinities and wide ranges of exposure.^[3]

Littorina obtusata are herbivores that primarily eat algae. They scrape algae from surfaces using their radula which contains thousands of tiny teeth.^[10] They are commonly associated with, and feed upon, the dominant intertidal brown algae, Ascophyllum nodosum.^[11]

Littorina obtusata are very good at adapting to new areas and predators. Their largest predator is the Carcinus maenas, the green crab. As the threat of these crabs raised, Littorina obtusata's shells have thickened to protect themselves.^[12] Wader birds also threaten Littorina obtusata's population. They forage in intertidal zones, preferring the low-water mudflats, but when they are submerged, they use the Ascophyllum/Fucus belts ^[4]