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Neritina pulligera
Species of gastropod From Wikipedia, the free encyclopedia
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Neritina pulligera, also known as dusky nerite, black racer, black helmet snail, or steel helmet snail, is a species of freshwater snail of the family Neritidae.[4] It is the type species of the genus Neritina.[5]
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Subspecies
There are two subspecies:
Description
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Perspective
The shell of N. pulligera is thick and typically measures 20 – 26 mm in length, although some individuals can reach 40 mm.[6][7] It is oval with a large opening (aperture), with an orange band running along the inside of the aperture.[8] The spire (coiled tip of the shell) is very low, but has a distinct apex (pointed tip of the shell).[9][10] At the aperture, the outer margin (lip) forms a small ridge toward apex. The inner lip is broad and has a thick, flat area (callus) which covers part of the aperture. This callus has a bluish-black colour on the outer side which gradually fades toward the inner side.[8][11] It is also slightly toothed at the inner edge. The shell colour varies from pale olive-green to dark brown or black.[10][9] It covers almost the entire body of the snail, such that the foot barely shows and only the tentacles stick out.[12]
The operculum, a "trapdoor" used by the snail to close its shell, is slightly convex on the outside with fine lines running lengthwise. Its back end is pale tan, while the front is pinkish with dark blue circular streaks in-between. From the inside, the operculum is slightly concave and dirty green with rosy white spots.[13]
Like other members of the subfamily Neritimorpha, N. pulligera presents a particularly convoluted protoconch (the earliest shell formed during the larval stage), with each new whorl overlapping the earlier one. Specifically in N. pulligera, it displays prominent ridges running lengthwise along the last half-whorl.[11]
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Distribution
N. pulligera originated in Southeast Asia, based on fossils of the Pliocene and Pleistocene ages found in Java. It occurs as a native species across the Indo-west Pacific. Records include India (Andaman and Nicobar Islands), Madagascar, northern Australia, Mozambique, South Africa (KwaZulu-Natal), and the Comoro Islands.[6][14][15] It has also been reported as a native from Japan.[16]
Following the IUCN Freshwater Biodiversity Assessment between 2003 and 2009, N. pulligera was classified as a species of Least Concern (LC) for southern Africa,[17] but as Near Threatened (NT)[18] in the pan-African scope.
Its type locality is "in Indiæ fluviis".[6]
Ecology
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Habitat
N. pulligera lives in fast-flowing streams and rivers with rocky substrates.[19] It colonises the entire freshwater course and can be found as far downstream as areas near the tidal influence of the ocean, such that it is also found in brackish waters.[20][21] It is often found in groups on boulders or coral blocks under moderate currents (20 – 50 cm/sec), but take shelter next to the stones facing away from the current when it becomes too strong (1 m/sec).[20] N. pulligera is most commonly reported under warm water temperatures (between 23 - 29 °C),[20][22] such that it is mostly found in low elevational zonations.[23]
Reproduction
Like other neritids, N. pulligera lays its eggs inside a hard calcareous capsule, produced by a specialised organ in female snails called the crystal sac. The capsules of N. pulligera are relatively large compared to other Neritidae, about 2.11 x 1.57 mm on average, and are elliptical in shape. They are laid in clusters of 9 - 39 capsules. Like other neritids, N. pulligera presents a unique egg-laying behaviour by preferably laying its eggs on the shells of other living snails. This, together with the reinforced capsules, helps protect the eggs from predation by other snails. These snails must scrape the capsule surface with their radula for several minutes to access the eggs, which is made especially difficult when they are on moving shells.[24]
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Human relevance
N. pulligera is used for food in some parts of Viti Levu, Fiji.[25]
References
Further reading
External links
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