Dear Recorder,
The identification of P. ulyssiponensis is often more complex than most publications suggest. If your specimen is a dead, fresh shell, please remove loose debris and position it carefully to take views 1-3, as above. A single, exterior, top view is very unlikely to be sufficient for verification. Some intermediate specimens may not be identifiable.
Records for P. ulyssiponensis can only be verified on iRecord, or agreed on iNaturalist, with images that show an adequate combination of some or all of these features:
1) low to medium height shell, usually less than 40% of length (insufficient alone as P. vulgata and P. depressa also have these forms). NOT a very high shell with height 50% or more of length (in Britain, only P. vulgata goes over 50%, such as 53 Patella ulyssiponensis album. COMPARISON image of P. vulgata, shell-length 46mm, that might be mistaken for high profile P. ulyssiponensis.. )
2) apex of shell offset towards anterior (insufficient alone as applies also to P. depressa).
3) shell interior of large, well-calcified adults may be entirely porcelaneous white 01 Patella ulyssiponensis. Length 50.5mm. Kincardine, Scotland. August 1970. and conceal the outer shell pattern (beware, some P. vulgata are similar, see image and caption at 53 Patella ulyssiponensis album. COMPARISON image of P. vulgata, shell-length 46mm, that might be mistaken for high profile P. ulyssiponensis. ) . Many shells have a varying amount of orange 14 Patella ulyssiponensis. Lengths 28.1mm, 39.5mm & 44.5mm. Lleyn. Wales. October 2015. and white parts may iridesce bluish. The foregoing description, or part of it, is that used in most publications, but very many, especially smaller ones, show the exterior pattern clearly through the inner layer and are very variable. To see the range, view images 1 to 31 at flic.kr/s/aHskqnXPqt ; these are easily confused with some forms of P. vulgata or P. depressa and may need views of soft parts for reliable det.
4) foot is NOT pitch-brown/black or dark khaki. It can be whitish when young 30 Patella ulyssiponensis. Pallial tentacles and foot from three small specimens; shell lengths 10.6mm, 12mm & 17mm. North Yorkshire. September 2014. becoming yellowish 31 Patella ulyssiponensis. Pallial tentacles and foot of three adults; shell lengths 20.3mm, 24.7mm & 26.8mm. North Yorkshire. September 2014. and, sometimes, orange with age 21 Patella ulyssiponensis. Pallial tentacles and foot of three large adults; shell lengths 39.6mm,40mm, & 40.5mm. North Yorkshire. September 2014. . Juveniles under 12mm length may show a blackish internal shadow through the thin pale translucent foot 30 Patella ulyssiponensis. Pallial tentacles and foot from three small specimens; shell lengths 10.6mm, 12mm & 17mm. North Yorkshire. September 2014. as they lack gonads above the foot that mask the dark viscera in adults. Foot colour alone is not sufficient for det. as P. vulgata can have most of these colours, and more besides.
5) basal half of pallial tentacles has opaque pigment which can be white or, on large specimens, yellowish, or orange (5 in image above). The distal half fades to a translucent tip. Opaque basal half is often distinct from translucent mantle-skirt that tentacles arise from, so it is possible to confuse with P. depressa. It is important to use pallial tentacles in combination with foot colour for identification. Examples at 26 Patella ulyssiponensis. Pallial tentacles from four specimens. Shell lengths 10.6mm, 12mm, 17mm and 40mm North Yorkshire. September 2014. .
6) on rocky shores all around Britain, except two areas with the coldest water in winter and high turbidity, i.e. S.E. England from Flamborough Head to Kent (perhaps Bognor Regis), and N.E. Irish Sea from Great Orme to (?)Ardwell, Rhins of Galloway. Lower shore and frequent at higher levels in pools lined with encrusting calcareous algae. Often the commonest Patella on shores exposed to strong waves.

Records claimed within the two excepted areas require 4 & 5 for verification, and such records with adequate evidence would be particularly welcome from Kent to Bognor and from south coast Scotland as the precise limits are uncertain. For full details please read the account at flic.kr/s/aHskokisge .

If using historic publications or transferring historic records be aware that pre 1923, and for some time after, the name ‘Patella depressa’ was used in error for what is now accepted as Patella ulyssiponensis. See synonyms section at 02 Patella ulyssiponensis. Length 18.7 mm. North Yorkshire. September 2014. .

Because P. depressa is apparently one of the commonest limpet species in southern Europe there seems to be a tendency on iNaturalist for records of any limpet there to be identified as it by some recorders by default. There are very few records in Atlantic Iberia on iNaturalist of P. ullyssiponensis, which is curious as “ulyssiponensis” means “from Lisbon”! Please consider it when recording in Iberia but make sure to include sufficient features for identification as, when only a single exterior dorsal image is shown, the generalised suggestion of ‘Patellogastropoda’ is all that can be reliably suggested.
For Atlantic coasts of Iberia, a useful aid is Trigo et al. 2018. Guia de los Moluscos Marinos de Galicia.
There is a widely differing variety of “P. ulyssiponensis” images, from the Mediterranean, on iNaturalist at www.inaturalist.org/taxa/450561-Patella-ulyssiponensis/br…. They cannot all be P. ulyssiponensis. Those with only an exterior view are not identifiable as it and should be marked as “Patellogastropoda” in my opinion. Some show the interior of beached strandline shells. If not freshly dead, the colour is apt to be bleached by the powerful Mediterranean sun, so they are of little use for identification.
The morphological features of P. ulyssiponensis, P. depressa, P. vulgata and (in Spain) P. rustica show “high morphological plasticity and are influenced by environmental conditions, leading to an overlap of states between different species”. Allozyme studies showed “high differentiation and no evidence of hybridisation” of the species (Sá-Pinto et al. 2007 www.vliz.be/imisdocs/publications/131981. pdf ). Individuals with intermediate morphological characteristics result from the accentuated morphological plasticity of these species, not hybridisation. Without molecular examination, they often cannot be confidently assigned to a particular species and should not be recorded as such.

OTHER SPECIES ALBUMS
marinvert.senckenberg.science/image-browse/