Mussel Terms

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Mussel Terms
2013-08-11 22:37:22
Freshwater Mussels

Glossary of bivalve terms from Art Bogan's NC bivalve workbook.
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  1. Alate
    with an extension or wing on the dorsal edge of the shell
  2. Angular (subangulate)
    having either the anterior or posterior margins forming are latively acute (sharp) angle
  3. Anterior
    front or forward
  4. Arcuate
    bent in a bow or arched
  5. Beak
    the raised portion of the dorsal margin of a shell; formed by the embryonic shell around which the rest of the shell develops distally in a concentric manner

    Also, the "Umbo"
  6. Beak cavity
    the cavity on the inside of each valve leading into the beak, under the interdentum
  7. Beak sculpture
    raised ridges or undulations on the umbo
  8. Biangulate
    having two angles
  9. Bradytictic
    mussels which are long-term breeders; females retain glochidia in their gills typically over the winter
  10. Byssus, byssal threads
    a bundle of tough threads secreted by the byssal gland in the foot of a bivalve, used to anchor the bivalve to some hard substrate
  11. Cardinal teeth
    teeth located between the lateral teeth in Corbiculidae and Sphaeriidae. Chevron - shaped like a wide-angled V
  12. Clinal variation
    the graded variation in morphology exhibited by a species in mollusks from headwater areas to the mouth of the highest order stream
  13. Compressed (subcompressed)
    flattened out or pressed together
  14. Concentric
    having a common center, such as ridges or loops radiating from the beak of a mussel valve
  15. Conspecific
    pertaining to individuals or populations of the same species
  16. Corrugated
    marked by wrinkles or ridges and grooves
  17. Crescentic
    shaped like the figure of the crescent moon with a convex and a concave edge
  18. Decorticate
    to remove the outer covering, in mollusks the epidermis
  19. Disc
    the middle or central portion of the exterior of a valve; distinct from the posterior slope or other areas immediately adjacent to the margin of the valve
  20. Discoidal
    round and flat like a disc
  21. Dorsal
    the top or back; in mussels, the hinge area
  22. Edentulous
    lacking both pseudocardinal and lateral teeth
  23. Effuse
    spread out broadly
  24. Elliptical (subelliptical)
    elongated, having the formof an ellipse
  25. Elongate
    long or extended
  26. Emarginate
    having a shallow notching at the margin
  27. Endangered
    this status at the state level includes peripheral forms which may be common in another part of its range, but whose continued existence within the political boundaries of the state is in danger of extirpation. At the national level, this status means the organism is in danger of extinction, and included on or being considered for the U.S. List of Endangered Fauna and Endangered and Threatened Plant Species of the United States, under the Endangered Species Act of 1973 (Cooper et al., 1973:x).
  28. Epidermis
    exterior or outside (corneous) layer of the shell
  29. Extinct
    a species which has no living representatives; all individuals are no longer extant
  30. Extirpated
    the extinction of a species within a portion of its range
  31. Form
    an animal with questionable taxonomic status; that is, one exhibiting variation but the extent or degree is not well enough known to determine whether it is a species, subspecies or simply individual or population variation
  32. Fusiform
    tapering toward each end
  33. Gills
    a thin plate-like paired structure within the mantle cavity, which serves as a respiratory organ in aquatic mollusks and in female unionids all of the gills or certain portions of the gills serve as the marsupium
  34. Globose
    globe-like, spherical
  35. Glochidium(plural - glochidia)
    the bivalve larvae of unionids which are generally parasitic on the gills of fish
  36. Gravid female
    a female that has embryos in the marsupium
  37. Growth lines
    compact lines of temporarily arrested growth or rest periods appearing on the epidermis of the shell as a raised or darker concentric line
  38. Hinge ligament
    an elastic, elongate, corneous structure that unites the two valves dorsally along the hinge plate
  39. Holotype
    single specimen designated as the "type" by the author inthe publication of a new species level taxon. Inequilateral - ina bivalve, having the two ends unequal, i.e., one end is wider or thicker than the other
  40. Inflated (subinflated)
    moderately to greatly inflated.
  41. Interdentum
    a flattened area of the hinge plate between the pseudocardinal and lateral teeth
  42. Iridescent
    showing colors like those of a rainbow
  43. Lachrymose
    termdescribing teardrop-shaped pustules
  44. Lateral teeth
    the elongated, raised and interlocking structures along the hinge line of the valve
  45. Lectotype
    one of a series of syntypes that, subsequent to the publication of an original description of a species level taxon, is selected (by publication) to serve as the type specimen for that taxon
  46. Lunule
    depressed area immediately anterior to the umbo
  47. Marsupial swelling
    a section ofthe posterior ventral margin of the female unionid shell which is enlarged orinflated to provide space for expansion of the marsupium with the development of the glochidia
  48. Marsupium(marsupial pouch)
    in unionids, a brood pouch for eggs and developing glochidia, formed by a restricted portion of the outer gill, the complete outer gill or all four gills.
  49. Muscle scar
    the area of attachment of a muscle to the inside of the shell; e.g., the anterior adductor muscle scar is the location of attachment for the anterior adductor muscle.
  50. Nacre
    the interior iridescent,thin layer of a mussel shell.
  51. Naiad
    formerly a tribe of Mollusca nearly equivalent taxonomically to the family Unionidae, often used as a synonymof unionid
  52. Nodule (subnodulous)
    a small rounded mass of irregular shape
  53. Oblique
    slanting; angled, butnot horizontal or vertical
  54. Obovate (subobovate)
  55. Orbicular (suborbicular)
    having the formof an orb; circular or nearly circular in outline
  56. Oval, Ovate (subovate)
    egg-shaped, broadly elliptical
  57. Pallial line
    an indented groove or line approximately parallel with the ventral margin of a bivalve shell that marks the line of muscles attaching the mantle to the shell
  58. Paratype
    each specimen of a type series other than the holotype designated in the original publication of the taxon.
  59. Periphery
    the external boundary on a surface, edge
  60. Periostracum
    see epidermis
  61. Plications
    parallel ridges on the surface of the shell.
  62. Posterior
    hind or rear
  63. Posterior ridge
    a ridge on the exterior of a mussel shell, extending from the umbo to the posterior margin
  64. Posterior slope
    the area across the dorsal portion of the valve extending from the umbo to the posterior margin, often above the posterior ridge
  65. Pseudocardinal teeth
    triangular-shaped hinge teeth near the anterior -dorsal margin of the shell.
  66. Pustule
    small, raised structure on the external oroutside surface of the shell (see also tubercle)
  67. Quadrate (subquadrate)
    square, or nearly square in outline
  68. Radial furrow
    a groove or depression; in naiads a groove running from the umbo area toward the shell margin.
  69. Radiating
    proceeding outward from a central point
  70. Rare
    seldom appearing, occurring widely separated in space; extremely few in number
  71. Rectangular
    a shape with four sides possessing four right-angles
  72. Rest mark
    see growth lines
  73. Rhomboid (subrhomboid)
    having generally four distinct sides, two sides being longer than the others
  74. Semicircular
    a partial or incomplete circle
  75. Serrated
    notched or grooved
  76. Sexual dimorphism
    a condition in which males and females of the same species are morphologically different, usually indicated by an expanded posterior marsupial area in the female in contrast to a more pointed or bluntly rounded area in the male
  77. Sinus
    a character of some unionids that have a depression above or below the posterior ridge
  78. Solid (subsolid)
    shells that are thick and heavy
  79. Special Concern
    This status covers cases where the organism exists in small populations over a broad range, may be over exploited which may pose a threat, the organism are especially vulnerable to specific pressures, or any other reasons identified by experienced researchers (Cooper et al., 1973:x)
  80. Species
    group of interbreeding natural populations that are reproductively isolated from all other such groups
  81. Striae
    impressed or raised lines on a shell
  82. Striate
    having striae
  83. Subspecies
    a geographically defined aggregate of local populations within a species that differ morphologically and/or physiologically from other aggregations of local populations within that species.
  84. Sulcus (plural - sulci)
    a longitudinal furrow or depression
  85. Sympatric
    pertaining to populations of two or more closely related species that occupy identical or broadly overlapping geographical areas
  86. Syntype
    one of a series of specimens of the same taxon that formed the material studied by the original author to describe a new species level taxon, form which no type specimen (holotype) was designated
  87. Tachytictic
    mussels which are short-termbreeders; i.e., glochidia are found in the gills of the female only during the summer
  88. Taxon
    any formal taxonomic unit or category of an organism; e.g., a species or genus
  89. Threatened
    This statusat the state level includes forms that are likely to become Endangered in the foreseeable future ifcertain conditions are not met. This includes forms that exhibit a considerable decrease in numbers beyond normal populations fluctuations or a documented range contraction, but are not yet considered Endangered. At the national level this applies to the Endangered Species Act of 1973 (Cooper et al., 1973:x).
  90. Trapezoid (subtrapezoid)
    a shape having four distinct sides with two sides parallel
  91. Triangular (subtriangular)
    a shape having three sides and three angles, like a triangle
  92. Truncate (subtruncate)
    having the end squared off
  93. Tubercle (tuberculate)
    small, raised, rounded knob on the outside of the shell
  94. Tuberculate
    having tubercles on the outside of the shell
  95. Type
    a designated specimen or specimens of an organism that serves as the basis for the original name and description of any species level taxon
  96. Umbo/umbone
    the dorsally raised, inflated area of the bivalve shell
  97. Unionids
    refers to any member of the freshwater bivalve mollusks that belong to the superfamily Unionoidea
  98. Undulation
    pattern with waves; raised ridges or bars
  99. Valve
    the right or left half of a mussel (or unionid) shell
  100. Ventral
    the underside or bottom