Lanistes solidus (Smith, 1877)
Species note: Lanistes solidus resembles Lanistes ellipticus.
Both species inhabit Lake Malawi, although at different habitats: Lanistes
solidus resides at the edge of the lake, whereas Lanistes ellipticus
is more abundant in the marshes surrounding the lake. Also, Lanistes solidus
is endemic to Lake Malawi, while Lanistes ellipticus can be found at
many places in Central and Southern Africa. Nevertheless, Lanistes solidus
could be considered a heavier, lacustrine (lake specific) form of Lanistes
Shell: Lanistes solidus is a rather small ampullarid snail. The average shell height is around 27 mm, with some shells growing to a 40 mm height. The spire is low and the shell has round body whorls. The shell itself is relatively thick and heavy. The umbilicus is narrow. There are no spiral bands on the brown shell of this species.
Operculum: The operculum is corneous. The structure is concentric with the nucleus near the centre of the shell.
Body: Brown foot with small light speckles equally distributed over the sole and whole visible body.
Eggs: The aquatic eggs are encapsulated in a gelatinous mass and deposited on the vegetation.
Food: Lanistes solidus eats algea from solid surfaces, in combination with dead and decaying plant materials and occasionally it eats animal matter.
Habitat: Lanistes solidus resides on the Potamogeton - Vallisneria vegetation at the sandy, shallow edges of the Lake Malawi Lake. Prefers depts to 4-5 m.
In Lake Malawi there is a annual cycle of a hot, wet season (January-April) at which the temperatures of the water can be 29°C and a dry, colder season (June-August), in which the temperature drops to around 20°C.
Behaviour: This snail species is mostly active during the night (noctural). During the day the snails are inactive and hide in the vegetation and the bottom. This behaviour is probably an adaptation to avoid being predated on by the molluscivorous cichlids in the lake, which hunt on vision.
Lanistes solidus is active throughout the whole year, and doesn't have an aestivation period in, which the snails stays dormant in the mud. As one realizes that Lake Malawi doesn't dry out, that the temperature stays acceptable for these snails, and the fact that food can be found the whole year round, on can imagine that there is no need to aestivate for these snails. Nevertheless, the activity and number of snails vary with the seasons (less snails in the cold, dry period). It has also been reported that these snails move to deeper water (10 m) during the cold, dry season.
Distribution: Lanistes solidus is endemic (lives only there) to Lake Malawi (Central Africa). Lanistes nasutus and Lanistes nyassanus are also endemic to this Lake.
Similar to: Lanistes solidus is closely related to Lanistes nyassanus, Lanistes ellipticus and Lanistes nasutus. The latter (nasutus) is found in deeper places of the Lake, is smaller (40 mm), has a thinner shell and has a narrow umbilicus. The first one (nyassanus) is larger, has a closed umbilicus and has a more depressed appearance. The larger (up to 50 mm) Lanistes ellipticus resides at the marshes surrounding Lake Malawi, and is not endemic to this lake, both is distributed over whole Central and Southern Africa.
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