MolluscIreland - land and freshwater
  • Assiminea (Assiminea) grayana Fleming 1828 Dun sentinel
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Assiminea (Assiminea) grayana
© Dr Roy Anderson
Assiminea (Assiminea) grayana
© Dr Roy Anderson

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A small but solid, rather pretty, operculate shell forming an almost perfect cone shape with glossy yellow-brown surface often with a broad red-brown band on the lower body whorl. Confined to estuaries.

Key characteristics

  • Shell small, solid, forming an almost perfect short cone with flat sutures between the whorls
  • Colour olive- to yellow-brown, often with a broad red-brown band on the body whorl and with the upper whorls a uniform red-brown
  • Aperture closed by an operculum

Size

4-6 mm.

World Distribution

Until recently this species was thought to be confined to the coasts of the North Sea with sites in Denmark, the Netherlands and south-east England. It has recently been reported from southern Ireland (Colville, 1992) and has also spread to north-west England. Distribution type: restricted Oceanic Temperate (71).

Irish Distribution

The Irish sites are all on the Shannon Estuary (Colville, 1992) and include Ferry Bridge on the River Maigue, Limerick, on the south side of the Estuary, and Clarecastle on the River Fergus, Clare, on the north side. Colville (1992) was of the opinion that it had appeared recently at these sites since the species was not detected by Phillips (1909) on visits there, although he recorded its associate Mercuria confusa. The Irish sites are also very disjunct from its North Sea centre of distribution (Kerney, 1999). To Colville’s sites the banks of the Bunratty River near Bunratty Castle in Clare can now be added (RA, August 2001) and Bunlicky Bridge, Ballincurra Creek (RA, October 2008). It is likely to be widespread in semi-saline environments throughout the inner part of the Shannon Estuary.

Ecology

  • Often on glutinous calcareous mud at the base of Phragmites well within tidal range on the banks of tidal streams
  • To a lesser extent beyond the normal tidal range in freshwater Iris marshes or grassy puddles with Oxyloma elegans and other amphibious species

Taxonomy

Like Hydrobia acuta and perhaps the Mercuria found on British coasts, this species may turn out to be synonymous with various southern European and Mediterranean forms currently given specific rank, and therefore to have a Mediterranean-Atlantic distribution. Giusti et al. (1995) argue that grayana may be the correct name, as the oldest epithet in currency, for a common Tyrrhenian Assiminea which is currently known as A. littorina (Delle Chiaie 1828).

Red List status

  • Not applicable (suspected invasive rather than native).

Wikipedia link

Wikipedia page for Assiminea grayana

 Anderson, R., (2016). Assiminea (Assiminea) grayana Fleming 1828. [In] MolluscIreland.
http://www.habitas.org.uk/molluscireland/species.asp?ID=38 Accessed on 2017-10-17.