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• Gyraulus (Armiger) crista (Linnaeus 1758) Nautilus ramshorn

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© Dr Roy Anderson

A tiny loosely coiled shell with body whorl below the rest to create a flat spire. Whorls are traversed by radial ridges which may form conspicuous narrow keels at regular intervals. Surface pale brown, glossy but often covered with deposits. Widespread.

Key characteristics

• A tiny loosely coiled shell with a low, flat spire
• Whorls convex with weak to very strong and regular radial ridges
• The ridges may form points on the periphery creating narrow keels
• Shell surface smooth, brown, slightly glossy but usually obscured by deposits
• Body whorl bluntly margined below, mouth oval to slightly angular
• (Technically it has always been difficult with planorbids to decide whether the raised whorls form a spire or an umbilicus! In these accounts the raised part is called (commonsensically) a spire even even though most experts regard it as an umbilicus)

Size

2-3 mm.

World Distribution

Spread across the northern part of the whole northern hemisphere. Distribution type: Circumpolar Wide-temperate (66).

GBIF distribution map [open in new tab]

Irish Distribution

Very widespread and locally common but much under-recorded because of its size.

Ecology

• A species of clear, weedy conditions in still water habitats
• Common in medium to very small habitats including sluggish streams, drains and marsh or fen pools
• Occasionally found in very acid waters
• Habitat size appears to be little impediment to this species - a thriving colony lives in a tiny ornamental pool (3m across) at the Lion's Gate, Mussenden Temple on the north Londonderry coast in water at best 2-3cm deep

Red List status

• Least concern (lc).

Wikipedia link

Wikipedia page for Gyraulus crista