Painted keyhole limpet Fissurella picta, photographed by Jan Delsing.

Belongs within: Fissurellidae.

Fissurella is a genus of keyhole limpets with the apex of the shell nearly central and the inner margin of shell smooth or weakly crenulate (Knight et al. 1960).

Peering through a limpet’s keyhole
Published 4 September 2016
Keyhole limpet Fissurella latimarginata, copyright Jan Maximiliano.

In an earlier post, I introduced you to the slit limpets, conical- or flat-shelled gastropods in the family Fissurellidae that possess a longitudinal slit at the front of their shells in order to help achieve the imposrtant condition of having one’s anus as far away from one’s mouth as possible. The image above shows another member of the same family, but this time known as a keyhole limpet. In the keyhole limpets of the genus Fissurella, the slit has been closed off and modified into a rounded opening bound by a callus at the shell’s apex. The apex is located sub-centrally on the shell which is also radially ornamented (Simone 2008). Other interesting features of the genus include a tendency for the radula to be asymmetrical with the three- or four-cusped lateral teeth larger on one side than the other. Two related genera, Amblychilepas and Macroschisma, differ primarily in having larger soft bodies that cannot be retracted under the shell whereas Fissurella species are able to seal themselves in (Aktipis et al. 2011).

Fissurella volcano, copyright Jerry Kirkhart.

Various Fissurella species are found around the world. They have been divided between several subgenera, but Fissurella taxonomy is complicated by the fact that the overall shape of the shell is strongly affected by the nature of the substrate each individual makes its home. Truly reliable identification of distinct taxa requires detailed knowledge of the soft anatomy which is apparently still little-known for many species. According to Simone (2008), there is a correlation between shell height and energy level of each species’ preferred habitat: species found in higher-energy environments (such as shorelines subject to heavy surf) tend to have higher shells (which surprises me because, if you’d asked me to guess, I might have expected the opposite).

As far as humans are concerned, though, most keyhole limpets have fairly little economic impact. Larger species, which can get up to about ten centimetres in size (many are much smaller), are harvested for food around the coast of South America. I also came across a reference to a Fissurella species being regarded as a pest in abalone aquaculture, as both species are algae-grazers and compete for food. Other than that, one imagines that their pre-perforated shells could be very useful for children wanting to make a (possibly somewhat malodorous) necklace as a souvenir of a trip to the beach.

Systematics of Fissurella
<==Fissurella Bruguière 1789BR05 [=Fissurellus deMontfort 1810KC60]
    |--*F. (Fissurella) nimbosa (Linnaeus 1758) [=Patella nimbosa]KC60
    |--F. (Balboaina Perez-Farfante 1943) [=Balboina (l. c.), Balvoina (l. c.)]KC60
    |    `--F. (*B.) picta (Gmelin 1791) [=Patella picta]KC60
    |--F. (Carcellesia Perez-Farfante 1952)KC60
    |    `--F. (*C.) doellojuradoi Perez-Farfante 1952KC60
    |--F. (Clypidella Swainson 1840)KC60
    |    `--F. (C.) punctata Fischer 1857KC60 (see below for synonymy)
    `--F. (Cremides Adams & Adams 1854)KC60
         |--F. (*C.) alabastrites Reeve 1849KC60
         |--F. (C.) clenchi Pérez Farfante 1943BC01
         `--F. (C.) deroyae McLean 1970BC01
Fissurella incertae sedis:
  F. albaC64
  F. altaC64
  F. calyculata Sowerby 1823H09
  F. elongata Philippi 1845H09
  F. excelsa [incl. F. panamensis]C64
  F. gibberulaBBB-S95
  F. lanceolata Sowerby 1862H09
  F. latimarginataM84
  F. macrotremaC64
  F. mesoatlantica Simone 2008S11
  F. mexicanaC64
  F. microtremaC64
  F. minuta Lamarck 1822H09
  F. musC64
  F. nigrocinctaC64
  F. nigropunctataC64
  F. nubecula (Linnaeus 1758)APB17
  F. obscuraC64
  F. octagona Reeve 1850H09
  F. peruvianaC64
  F. radiataG79
  F. rosea (Gmelin 1791) [=Patella rosea]BC01
  F. rubropictaM84
  F. rugosaC64
  F. tenebrosaC64
  F. virescensC64
  F. volcano Reeve 1849O27 [incl. F. ornataC64]
    |--F. v. volcanoO27
    `--F. v. crucifera Dall 1908O27

Fissurella (Clypidella) punctata Fischer 1857KC60 [incl. Patella pustula Gmelin 1791 non Linnaeus 1758KC60, *Clypidella pustulaKC60, Fissurella punctata var. rosea Usticke 1969 non Patella rosea Gmelin 1791BC01]

*Type species of generic name indicated


Aktipis, S. W., E. Boehm & G. Giribet. 2010. Another step towards understanding the slit-limpets (Fissurellidae, Fissurelloidea, Vetigastropoda, Gastropoda): a combined five-gene molecular phylogeny. Zoologica Scripta 40: 238–259.

[BBB-S95] Boubezari, K., G. Bitar & D. Bellan-Santini. 1995. Structure et organisation de trois moulières (Mytilus galloprovincialis et Perna perna) de la région d’Alger. Mésogée 54: 63–72.

[BR05] Bouchet, P., & J.-P. Rocroi. 2005. Classification and nomenclator of gastropod families. Malacologia 47 (1–2): 1–397.

[BC01] Boyko, C. B., & J. R. Cordeiro. 2001. Catalog of Recent type specimens in the Division of Invertebrate Zoology, American Museum of Natural History. V. Mollusca, part 2 (class Gastropoda [exclusive of Opisthobranchia and Pulmonata], with supplements to Gastropoda [Opisthobranchia], and Bivalvia). Bulletin of the American Museum of Natural History 262: 1–170.

[C64] Carpenter, P. P. 1864. Supplementary report on the present state of our knowledge with regard to the Mollusca of the west coast of North America. Report of the British Association for the Advancement of Science 33: 517–686.

[G79] Guppy, R. J. L. 1879. First sketch of a marine invertebrate fauna of the Gulf of Paria and its neighbourhood. Part I.—Mollusca. Journal of Conchology 2: 151–172.

[H09] Hedley, C. 1909. The Marine Fauna of Queensland: Address by the President of Section D. Australasian Association for the Advancement of Science: Brisbane.

[KC60] Knight, J. B., L. R. Cox, A. M. Keen, R. L. Batten, E. L. Yochelson & R. Robertson. 1960. Gastropoda: systematic descriptions. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I169–I331. Geological Society of America, and University of Kansas Press.

[M84] McLean, J. H. 1984. A case for derivation of the Fissurellidae from the Bellerophontacea. Malacologia 25 (1): 3–20.

[O27] Oldroyd, I. S. 1927. The Marine Shells of the West Coast of North America vol. 2 pt 3. Stanford University Press: Stanford University (California).

Simone, L. R. L. 2008. A new species of Fissurella from São Pedro e São Paulo Archipelago, Brazil (Vetigastropoda, Fissurellidae). Veliger 50 (4): 292–304.

[S11] Simone, L. R. L. 2011. Phylogeny of the Caenogastropoda (Mollusca), based on comparative morphology. Arquivos de Zoologia 42 (4): 161–323.

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