Tectus niloticus (Linnaeus, 1767)
100mm or more

Tectus niloticus is abundant on hard substrate on intertidal, lagoon, pinnacle and seaward reefs at Kwajalein, but that has not always been the case. Despite its current abundance, this species is not native to the Marshall Islands, but was intentionally introduced by man to establish a commercial fishery. According to Gillett (2002), the first recorded introductions to the Marshalls were in 1939 when separate shipments from Chuuk and Palau were made to Jaluit Atoll. From these two small events, the species has spread and become the most abundant large gastropod in the Marshall Islands. Sometimes called the "commercial top shell," Tectus niloticus (formerly in the genus Trochus), has a thick layer of mother-of-pearl beneath the outer shell layer, which can be exposed by carefully treating the shell with acid. Shells are harvested in some places to produce mother-of-pearl buttons. Although I have not heard of any button industry in the Marshalls, because of the commercial potential, Kwajalein authorities at the army base have placed Tectus niloticus in a protected status to keep it from being collected, a rather ludicrous situation since protection is usually reserved for native threatened species and not for abundant introduced exotics. The species is gathered to a certain extent by Marshallese residents for food.

Four shells exposed on the intertidal reef flat.

Spawning. These animals release large numbers of eggs and sperm, and fertilization takes place in the surrounding water.

One animal that has appreciated the introduction of Tectus niloticus to the Marshalls is apparently the octopus. It is common to find piles of old or new empty Tectus shells piled up in what seem to be octopus dining areas. It is as though the octopus gathers shells from different places and takes them to the same place to eat. Sometimes it is clear the feeding area has been in use for some time, since more recently emptied shells are at the top of a pile of shells that appear to gradually get older the deeper they are in the pile.


Gillett, R. 2002. Pacific islands trochus introductins 1927-1988. SPC Trochus Information Bulletin #9, Nov. 2002.

Created 26 April 2017

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