The Pectinidae (from the Latin pecten meaning comb), common name scallops, are a family of saltwater bivalve mollusks. They are hermaphrodites, and the male gonads mature first. Numerous species of various sizes occur in all of the oceans, and a number species are of commercial importance as food species.

A small minority of pectinid species live cemented to rocky substrates as adults. Some others species are more simply attached, by means of a filament they secrete. The majority of species, however, are recumbent on sandy substrates, but when they sense the presence of a predator such as a starfish, they are able to escape by swimming swiftly but erratically through the water using a form of jet propulsion created by repeatedly clapping the valves of their shell together.

Pectinids have numerous simple eyes situated around the edges of their mantles.

Shell morphology

In general, shells of the Pectinidae consist of two valves which are circular to broadly ovate with the right valve usually more inflated than the left valve. The valves are narrower and pointed at the umbones, which have flattened triangular extensions on both sides, known as auricles or ears. The upper edge of the ears forms a somewhat straight hinge line. The umbones project only slightly above this line. Most Pectinidae have radial ribs and concentric ridges, although a few are smooth. The ctenolium is a key shell feature that separates Pectinidae from all other families.

Distribution and habitat

Pectinidae inhabit all the oceans of the world, with the largest number of species living in the Indo-Pacific region. Most species live in relatively shallow waters from the low tide line to 100 meters, while others prefer much deeper water. Although some species only live in very narrow environments, most are opportunistic and can live under a wide variety of conditions. Pectinidae can be found living within, upon, or under either rocks, coral, rubble, sea grass, kelp, sand, or mud. Most adult specimens are either byssally attached or cemented to a substrate, while others are free swimmers.

Fossil record

Fossil Pectinidae from East Timor

The fossil history of Pectinidae is rich in species and specimens. The earliest known records of true Pectinidae (those with a ctenolium) can be found from the Triassic period over 200 million years ago.^[1] The earliest species were divided into two groups, one with a nearly smooth exterior: Pleuronectis von Schlotheim, 1820, while the other had radial ribs or riblets and auricles: Praechlamys Allasinaz, 1972. ^[2] Fossil records also indicate the existence of Pectinidae has been unstable at times; from being the most speciose family of the Mesozoic era, to almost disappearing completely by the end of the Cretaceous period. Survivors evolved rapidly during the Tertiary period. Nearly 7,000 species and subspecies names have been introduced for both fossil and recent Pectinidae.

Taxonomy and list of genera

More than 30 genera and around 350 species are in the family Pectinidae. Raines and Poppe^[3] list nearly 900 species names, but most of these are considered either questionable or invalid. They mention over 50 genera and around 250 species and subspecies. While species are generally well circumscribed, their attribution to subfamilies and genera is sometimes equivocal, and information about phylogeny and relationships of the species is minimal, not the least because most work has been based on adult morphology.^[4]

Genera

Family Pectinidae

• Subfamily Camptonectinae Habe, 1977
  • Delectopecten Stewart, 1920
  • Ciclopecten Seguenza, 1877
  • Lyropecten Conrad, 1862
  • Pseudohinnites Dijkstra, 1989
• Subfamily Hemipectinae Habe, 1977 (disputed, often in Chlamydinae: Chlamydini)
  • Hemipecten Adams & Reeve, 1849
• Subfamily Palliolinae Korbkov in Eberzin, 1960
  • Tribe Palliolini Waller, 1993
    • Palliolum Monterosato, 1884
    • Lissochlamys Sacco, 1897
    • Placopecten Verrill, 1897
    • Pseudamussium Mörch, 1853
    • Mesopeplum Iredale, 1929
• Subfamily Pectininae
  • Tribe Decatopectinini Waller, 1986
    • Anguipecten Dall, Bartsch & Rehder, 1938
    • Annachlamys Iredale, 1939
    • Bractechlamys Iredale, 1939
    • Decatopecten Rüppell in G. B. Sowerby II, 1839
    • Excellichlamys Iredale, 1939
    • Flexopecten Sacco, 1897
    • Glorichlamys Dijkstra, 1991
    • Gloripallium Iredale, 1939
    • Juxtamusium Iredale, 1939
    • Mirapecten Dall, Bartsch & Rehder, 1938
  • Tribe Pectinini Wilkes, 1810
    • Amusium Röding, 1798
    • Dentamussium Dijkstra, 1990
    • Pecten Müller, 1776 (includes the Great or King scallop, Pecten maximus, Japanese (sea) scallop, Pecten yessoensis, the New Zealand scallop, Pecten novaezealandiae, and the Ravenel or Round-rib scallop, Pecten raveneli)
    • Euvola Dall, 1898 (includes the Zigzag scallop, Euvola ziczac)
    • Minnivola Iredale, 1939
    • Serratovola Habe, 1951
• Subfamily Chlamydinae von Teppner, 1922
  • Tribe Clamydini von Teppner, 1922
    

    

    Semipallium fulvicostatum
    • Chlamys Röding, 1798
    • Complichlamys Iredale, 1939
    • Coralichlamys Iredale, 1939
    • Equichlamys Iredale, 1929
    • Hinnites Defrance, 1821
    • Laevichlamys Waller, 1993
    • Manupecten Monterosato, 1872
    • Nodipecten Dall, 1898
    • Notochlamys Cotton, 1930
    • Pascahinnites Dijkstra & Raines, 1999
    • Pedum Bruguière, 1791
    • Psychrochlamys Jonkers, 2003
    • Scaeochlamys Iredale, 1929
    • Semipallium Jousseaume in Lamy, 1928
    • Swiftopecten Hertlein, 1936
    • Veprichlamys Iredale, 1929
  • Tribe Austrochlamydini Jonkers, 2003
    • Austrochlamys Jonkers, 2003
  • Tribe Adamussiini Habe, 1977
    • Adamussium Thiele, 1934
  • Tribe Fortipectinini Masuda, 1963
    • Mizuhopecten Masuda, 1963
    • Patinopecten Dall, 1898
  • Tribe Crassadomini Waller, 1993
    • Crassadoma Bernard, 1986
    • Caribachlamys Waller, 1993
  • Tribe Mimachlamydini Waller, 1993
    • Mimachlamys Iredale, 1929
    • Spathochlamys Waller, 1993
    • Talochlamys Iredale, 1935 includes Talochlamys pusio (Linnaeus, 1758) == Chlamys distorta (da Costa, 1778)
  • Tribe Aequipectinini F. Nordsieck, 1969
    • Aequipecten Fischer, 1886 (includes Rough scallop Aequipecten muscosus)
    • Argopecten Monterosato, 1889 (includes bay scallop, Argopecten irradians, Atlantic calico scallop Argopecten gibbus and Pacific calico scallop, Argopecten ventricosus)
    • Cryptopecten Dall, Bartsch & Rehder, 1938
    • Haumea Dall, Bartsch & Rehder, 1938
    • Leptopecten Verrill, 1897
      • Leptopecten latiauratus Conrad, 1837
    • Volachlamys Iredale, 1939
• Subfamily incertae sedis
  • Hyalopecten Verrill, 1897

Gallery

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  A live individual of Argopecten irradians, the Atlantic Bay scallop, photographed at the Marine Biological Laboratory in Woods Hole, Massachusetts

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  The great scallop, Pecten maximus, on the right, next to the native European oyster Ostrea edulis

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  A live individual of Placopecten magellanicus

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  A shell of a Pecten species withserpulid worm encrustation; Duck Harbor Beach on Cape Cod Bay,Wellfleet, Massachusetts

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  The fossil species Amusium cristatum from the Pliocene of Cyprus

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  External mold of a scallop shell in the fossil genus Aviculopecten, from the Logan Formation, Lower Carboniferous, Ohio.

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  Pedum spondyloideum from the North coast of East Timor

References

1. ^ Treatise on Invertebrate Paleontology Geological Society of America, Kansas, Part N, Vol. I (1969) p. N348.
2. ^ Waller, T. R. (1993): The evolution of "Chlamys" (Mollusca: Bivalvia: Pectinidae) in the tropical western Atlantic and eastern Pacific. American Malacological Bulletin 10 (2): 195-249.
3. ^ Raines, B. K. & Poppe, G. T. (2006): The Family Pectinidae. In: Poppe, G. T. & Groh, K.: A Conchological Iconography. 402 pp., 320 color plts., ConchBooks, Hackenheim, ISBN 3-925919-78-3.
4. ^ Barucca, M., Olmo, E., Schiaparelli, S. & Canapa, A. (2004): Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia)