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Lottia digitalis & pelta; Tectura persona & scutum (Finger limpet, Shield limpet, Mask limpet, & Plate limpet)
Copyright © 2006
Mary Jo Adams
Four species of limpets of somewhat similar appearance are found on rocky areas of Island County beaches. They are Lottia digitalis (the finger limpet), Lottia pelta (the shield limpet), Tectura persona (the mask limpet), and Tectura scutum (the plate limpet). There are subtle differences that help to distinguish between them. Viewed from above, all four species present an oval shape. The primary points of difference are in the relative height and location of the apex (the highest point of the shell) and the texture of the margin of the shell, i.e. is the margin smooth or does it have ridges.
Lottia digitalis (Finger limpet)
With a maximum length of 1-1/4 inches, Lottia digitalis is usually easy to identify because of the far anterior placement of the apex that may be in line with or even overhanging the anterior margin and pronounced ribbing that mark its shell. It is found high in the intertidal and splash zone on boulders and other rocks. Look for it especially along cracks and crevices, often clustering with others of its own and other species of limpets. This limpet is also found among goose barnacles. Lottia digitalis grazes on microalgae and fine filamentous algae. In turn, it becomes prey to birds, crabs, and fish. This limpet was previously known under the scientific name, Collisella digitalis. Another common name for it is “ribbed limpet”.
Lottia pelta (Shield limpet)
Because of Lottia pelta’s variable appearance, identifying it can be a challenge. The relatively high apex of this limpet is slightly off-center toward the anterior and the shell margin usually has ribbing but can also be smooth. It has a maximum length of 2-1/4 inches. This limpet is found on rocks, in mussel beds, and on feather boa kelp (Egregia menziesii) in the middle and low intertidal zones. It grazes on microalgae such as diatoms and also on encrusting and upright seaweeds including Petrocelis, Endocladia, Iridia cordata, and Egregia. The shield limpet is preyed on by the purple seastar (Pisaster ochraceous), the mottled sea star (Evasterias troschelii), the frilled dogwinkle (Nucella lamellosa), and also various species of fish and birds. The common and scientific names for this species mesh nicely because “pelta” is the Latin word for a small shield. This species has also been known as Collisella pelta but that name is no longer valid.
Tectura persona (Mask limpet)
Tectura persona is found in the upper and middle intertidal zones where it inhabits shaded areas of boulders and other rocks, often, congregating with other limpets. The apex is well offset from the center toward the anterior margin and the shell has an inflated or bloated appearance. The margin of the limpet is smooth and relatively thin. Maximum length of this species is 2 inches. Active at night, the mask limpet feeds on diatoms and other algae. Oystercatchers, crows, and other shorebirds make it their prey. A former scientific name for the mask limpet is Notoacmea persona and another common name for it is “speckled limpet”.
Tectura scutum (Plate limpet)
The plate limpet has a relatively flat profile with a low rounded apex. The apex lies near the center of the shell and the shell margins are smooth, giving it the appearance of an overturned dinner plate. In addition, it is the only limpet on the West Coast of the United States with brown tentacles. Its maximum length may exceed 2.5 inches and it inhabits rocks in the middle to low intertidal and ranging into subtidal depths. This species may have the green seaweeds Ulva or Enteromorpha, or even barnacles growing from the surface of its shell. Plate limpets feed on microscopic and encrusting red algae and are preyed on by crabs, seastars, birds, and fish. This species was previously called Notoacmaea scutum.
This
page was created by Mary Jo Adams on 5/24/06.
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