Suggestions for the collection, examination and
photography of rock dwelling Patella species.
Ian F. Smith, April 2020

Casual photographs of the shell exterior of Patella species are unreliable evidence for differentiation and are likely to be declined as records by verifiers on iRecord, especially when they would alter the established distribution patterns. In north-west Europe, if a lateral view shows that a shell has a height 50%, or more, of its length, it can usually be accepted as Patella vulgata (but it often has a lower shell). Otherwise, the interior of a fresh shell may suffice but, often, a view of the foot and peripheral pallial tentacles is needed. This requires removal, without damage, of a live limpet from the substrate.
Collecting equipment
Dining knife with a strong, broadly rounded tip (sharp point risks damage).
Plastic box, lined with polythene, part-filled with seawater.
Collecting method
Please be sparing in how many you take, especially if limpets are not locally common.
Carefully approach a limpet in a pool or on damp rock; its shell will probably not be applied with full force to the substrate. Sudden movement or shadow may cause it to clamp down. When close enough, quickly force the knife, angled into the rock under the shell and foot. A horizontal thrust risks lethal damage. If the rock is soft, try to push the knife tip into its surface. Complete the removal by striking the handle of the knife with your free hand, as if hitting a chisel. If your first thrust fails to go under the limpet, abandon the effort as it will have clamped down and be impossible to move without damage. Try another one.
Place the removed limpet, sole down, in the lined box in water sufficiently deep to cover the shell; there should be air left in the box. Leave the box undisturbed for the limpet to settle and grip the polythene before transporting it. Upturned limpets are likely to die, so check as soon as home is reached that it is still upright. If collecting more than one, place each in a separate box as if one dies it will foul the water and kill its companions. If processing is delayed, keep in a refrigerator at about 7°C.
If you decide to examine/photograph the limpet on the beach you can dispense with the box. If replacing a limpet, it should be at the spot where found.
Examination equipment.
1. Container about 4 cm deep with base painted with black bituminous paint (or clear base on top of black polythene).
2. Piece of glass that will fit inside container.
3. Four identical flat supports about 15 mm thick (e.g. dissection blocks).
4. Sea water.
5. Spirit-levelled work surface. e.g. an aquarium stand with top of toughened glass such as door off old audio system cabinet. On the shore do your best to level the container.

Examination method.
Take the polythene with limpet out of its box and slide the limpet off it onto the glass.
Place the glass on the supports in the container with seawater deep enough to just cover the glass.
When limpet has gripped the glass, turn glass over and replace on supports. If the limpet moves to the edge you can usually slide it to the centre without it detaching.
The expanded foot will now be visible. When the limpet has settled down it will likely extend its head and you may see the mouth open, and the radula make feeding strokes. Eventually, the mantle will expand to the shell’s rim, and the peripheral pallial tentacles will extend and be visible against the black base of the container.
Compare what you see with images in the accounts at flic.kr/s/aHskokisge and flic.kr/s/aHskqnXPqt ; both contain comparative images of P. vulgata. Magnification and good lighting will help.
Photography
If the shell height is 50%, or more, of the shell length, an untilted side-image showing its profile is usually sufficient evidence for P. vulgata in north-west Europe. Otherwise, a clear photograph of the vacant shell interior may be enough. If foot and pallial tentacles are used for positive identification, a clear record photograph is needed for acceptance as personal judgement about what is opaque white or translucent is subjective, especially until the different species have been experienced. (From this cause I initially made mistaken records which had to be removed from NBN maps.)
Cameras vary widely in what they can do. A digital SLR with manual focus, rack and pinion tripod and two side flashes, as in the image above, is ideal but expensive. A separate sheet is available for Nikon 300s which may be of use with other DSLRs. This article is to guide you to general principles that I hope you will find useful with automatic compact cameras, mobile phone cameras etc, as well as DSLRs.
If about to buy a compact camera, one that is put to very good use by many is the Olympus Tough TG series shop.olympus.eu/en_GB/cameras/tough/tg-6 . It can withstand being dropped and can even be used submerged in a pool. It can be used by divers to moderate depths, but may have a short life if used without a camera housing. It has a 12 megapixel image sensor. Cameras with fewer pixels will take poorer images, those with more should do better.
Camera Handbook It is essential to read the handbook to learn how to use different features on your camera. Keep a note of what you find useful. Use the camera for general photography before attempting close ups.
Focusing
For zoomed-in close ups the depth of field of focus is tiny. If the subject and lens surface are not parallel, one part may be in focus and the rest blurred.
1) Avoid tilting the camera or the subject/base of container (unless both tilted at same angle) if possible. The most reliable method is with camera facing vertically down mounted on a rack and pinion tripod with both work surface and back of camera levelled horizontal with a spirit level.
2) Avoid the slightest movement of the camera as the automatic focus is unlikely to adjust quickly enough to minor movement. Use tripod as in 1; otherwise use whatever is available to steady the camera with lens surface parallel to subject/container base. One impromptu shore technique used by A. Rowat when photographing with an Olympus TG, is to hold it in two hands and project his little fingers to rest against the substrate. If the telescopic legs are withdrawn to their minimum, a tripod is very stable and can be stood on a table with the subject raised for closer focusing on a rigid box on the table.
3) Zoom in (closeness possible varies with camera) to fill as much of the frame as is possible with the subject so the automatic focus adjusts to the subject rather than a larger expanse of background.
4) Keep the subject as close as possible to the background which is likely to be what it focuses on when it is not possible to fill the frame with the subject. Holding the subject in one hand and the camera in the other while standing on the shore is likely to give a focused image of the shore and a blurred image of the subject and hand, added to by unavoidable small movement.
5) Use flash, as with it the lens aperture will close to the minimum for the bright light it provides. Small apertures give sharper images than large ones. Images taken in weak light will cause the aperture to open wide and the result is likely to be blurred, or very dark if it doesn’t open.
Glare and reflection
In the open, a horizontal water surface reflects the sky, including clouds. This hinders what can be seen in the water and gives photos a milky appearance. Ask a companion to block the sky by holding a black umbrella, or similar, high above the container or pool containing the subject.
Indoors, a flash located on the top of a camera pointing vertically down emits light at 90° to the water surface, and the light reflects directly back on the same track into the lens causing glare. If the camera can be operated with flash units off the camera, two should be placed, one at either side, at c. 45° tilt to the surface. Flash units can be free standing or mounted on a lens bracket protruding right and left. The light then is reflected away at 45° in the opposite direction, not into the camera. If a single side flash is used, one side will be brilliant and the other in black shadow. To avoid this if only one is available, put a reflector of crumpled aluminium foil close to the subject on the side away from the flash. But many cameras only have the option of single top-mounted flash. In this case, deviate slightly from focusing item ‘1’ (above) by tilting the camera and flash up a little. Experiment to find the minimum tilt that will get rid of reflection; you may find that when zoomed in very close that the small distance between lens and flash is sufficient for the reflection to miss the lens, even when the camera is untilted.
Damp/wet shells have a curved surface that reflects at an infinite number of different angles. However you position the camera or light source, some light will enter the lens and cause glare. To avoid this, either dry the shell or submerge it completely and photograph it as above. If part protrudes from the water, the curved meniscus at point of emergence will cause glare.
Exposure
The automatic exposure of a camera sets itself according to brightness of what it senses in the frame. If a small dark subject is surrounded by a large white background the aperture reduces to avoid what it senses, mainly the white background, from being too bright. This results in a correctly exposed background and an underexposed dull dark image of the subject. To avoid this, try photographing with a black smooth background, such as a base painted with black bituminous paint or a clear base resting on black polythene. Avoid textured surfaces as they catch and reflect light. Different camera models vary, so you may need to experiment.
Editing
An editing suite can vastly improve images. Photoshop is the best known, but is expensive and complicated to use. A simpler, cheaper one may be easier to master.
There may already be some editing facilities on your pc; it is worth having a look. I use PhotoStudio 6, but it is no longer available for official sale. Features I find most useful are crop, rotate, auto enhance, sharpen, brightness, saturation, contrast, fill, clone, brush, text, and stitch. Practice is required to get the best from editing.