Vernacular names: Northern tortoiseshell limpet.
A more detailed account is available here: https://flic.kr/s/aHskbm8fpS
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Key identification features
1: Maximum length usually 20mm, occasionally 25mm, rarely 30mm.
2: Shell exterior matt-whitish with radiating chocolate-brown rays that often bifurcate and reunite across the shell 1Tt flic.kr/p/WadzLk .
3: Shell interior porcelaneous-white with brown-banded peripheral border, an amphora-shaped, chocolate-brown patch and a pale vertex patch 4Tt flic.kr/p/XbymyT .
4: No prominent sculpture (except sometimes irregular repair-line of damage), but many fine concentric growth lines and radiating striae 5Tt flic.kr/p/XoDw7c .
5: Mantle skirt with emerald green pigment dorsally that looks blue-green when viewed ventrally 17Tt flic.kr/p/X8KpZN . Green is sometimes very pale.
6: Large pallial tentacles protrude beyond shell perimeter when active 23Tt flic.kr/p/Xksgfj .
7: Northern species stretching south to southern Scotland, northern Ireland, Isle of Man, south-west Sweden and Rhode Island, USA.
8: Sometimes, but more often not, on pink, calcareous, encrusting algae with no pale feeding pits, and faecal rods with flat truncated ends that are not chalk-white.
Young Patella spp., can resemble worn specimens of T. testudinalis.
The only ‘tortoiseshell limpet’ in the southern half of Britain where it is often mis-recorded as Testudinalia testudinalis.
1: Maximum length 12mm.
2: Shell exterior whitish/yellowish/bluish with radiating pinkish rays and/or light-brown chains which are often mistaken for brown marks of T. testudinalis, especially small juveniles 42Tt flic.kr/p/XASHRd .
3: Shell interior white often translucent showing exterior marks, sometimes red-brown V near vertex 43Tt flic.kr/p/WCkdUp .
4: Sculpture of slight threadlike radiating striae 43Tt flic.kr/p/WCkdUp , often indistinct or absent 44Tt flic.kr/p/XASHz1 , and numerous fine concentric growth lines
5: Mantle-skirt white, yellowish, or blue-green with reddish bands on periphery 45Tt flic.kr/p/XfRfyN , 46Tt flic.kr/p/WA5eV5 and 47Tt flic.kr/p/XASHvo .
6: Outer edge of mantle has many small, unobtrusive, translucent processes and many large white repugnatorial glands pointing inwards from mantle edge, but no prominent, outward pointing, pallial tentacles 48Tt flic.kr/p/XRRcsx .
7: All round Britain except Liverpool Bay and parts of SE England.
8: Nearly always on pink calcareous encrusting algae with pale feeding pits and short, chalk-white faecal rods with hemispherical ends.
The map provided here shows the distribution of the species based on Conchological Society data held by the National Biodiversity Network (NBN). See terms and conditions.
The following datasets are included:
- Conchological Society of Great Britain & Ireland: marine mollusc records
Open an NBN Atlas interactive map of this data in a new window.
Taxon details available from MolluscaBase (AphiaID 234208):
Testudinalia testudinalis (O. F. Müller, 1776)
The UK NBN Atlas entry for the species can be accessed via this link.