MUSSEL

Graf & Cummings (2006):
Morphological Characters and States

Life-History Characters

Descriptions of the morphological characters and their states used to construct the matrix of morphological characters used by Graf & Cummings (2006) are given below. It is our intention to eventually illustrate as many of these as possible. Comments, suggestions and potential images should be forwarded to Dan Graf.

Characters are divided into six categories for convenience: Shell, Ctenidia and Labial Palps, Mantle, Other Soft-Anatomical, Life-History, and Larval. These characters have been largely drawn from those employed in published studies. Those previously used characters are coded with the following abbreviations:

  • G Graf, D.L. 2000. The Etherioidea revisited: a phylogenetic analysis of hyriid relationships (Mollusca: Bivalvia: Paleoheterodonta: Unionoida). Occasional Papers of the University of Michigan Museum of Zoology 729: 1-21.
  • GO Graf, D.L & D. Ó Foighil. 2000. The evolution of brooding characters among the freshwater pearly mussels (Mollusca: Bivalvia: Unionoidea) of North America. Journal of Molluscan Studies 66: 157-170.
  • GW Giribet. G & W. Wheeler. 2002. On bivalve phylogeny: a high-level analysis of the Bivalvia (Mollusca) based on combined morphology and DNA sequence data. Invertebrate Biology 121: 271-324.
  • HBH Hoeh, W.R., A.E. Bogan & W.H. Heard. 2001. A phylogenetic perspective on the evolution of morphological and reproductive characteristics in the Unionoida. pp. 257-280. In: Bauer G, Wächtler K, eds. Ecology and Evolution of the Freshwater Mussels Unionoida. Ecological Studies 145. Springer-Verlag, Berlin.
  • LMD Lydeard, C., M. Mulvey & G.M. Davis. 1996. Molecular systematics and evolution of reproductive traits in North American freshwater unionacean mussels (Mollusca: Bivalvia) as inferred from 16S rRNA gene sequences. Philosophical Transactions of the Royal Society of London B 351: 1593-1603.
  • RH Roe, K.J. & W.R. Hoeh. 2003. Systematics of freshwater mussels (Bivalvia: Unionoida). pp. 91-122. In: Lydeard C, Lindberg DR, eds. Molecular Systematics and Phylogeography of Mollusks. Smithsonian Series in Comparative Evolutionary Biology. Smithsonian Books, Washington DC.

Such citations follow the character description in squared brackets. Character state “X” refers to a condition that does not occur among the sample of taxa in our study but that has been of treated as a synapomorphy elsewhere.

42. Habitat. — 0 = Marine. 1 = Freshwater. [G/23; GO/1]

43. Parental care. — 0 = No parental care, with gametes of both sexes spawned freely. 1 = Ova fertilized and larvae brooded in the interlamellar spaces of the ctenidia. All Unionoida coded as brooding. [G/24; GO/2; GW/152-153]

44. Demibranchs occupied by marsupium. — 0 = Tetragenous (all four demibranchs). 1 = Endobranchous (inner pair of demibranchs only). 2 = Ectobranchous (outer pair of demibranchs only). Endobranchy is known from hyriids, mycetopodids, iridinids and etheriids. Tetrageny and ectobranchy occur in various lineages of the Unionoidea. Coded as “inapplicable” in non-brooding taxa. [LMD/1; G/25; GO/3; HBH/10, RH/21-23]

45. Brooding period. — 0 = Tachtictia. 1 = Bradytictia. Coded only for the Unioninae and Ambleminae, for which there is reliable data (Graf, 1997); coded as “inapplicable” among non-brooding taxa. Bradytictia occurs among the anodontine and lampsiline Unionidae (Graf & Ó Foighil, 2000). [LMD/2; GO/12]

46. Portion of the outer demibranch that is marsupial. — 0 = Entire outer demibranch. 1 = Only a central or posterior portion is utilized for brooding. The marsupium is restricted among lampsiline genera to only a portion of the outer demibranch. Coded as “inapplicable” among taxa that do not brood in the outer demibranchs. [LMD/12; G/26; GO/4; HBH/28(2); RH/56]

47. Portion of the inner demibranch that is marsupial. — 0 = Entire inner demibranch. 1 = Only a central portion is utilized for brooding. Among hyriids, the interlamellar septa are more dense in the central section of the marsupial demibranch where brooding occurs (McMichael & Hiscock, 1958). Coded as “inapplicable” among taxa that do not brood in the inner demibranchs. [G/27; HBH/28(1); RH/57]

48. Subdivision of marsupial water-tubes. — 0 = Not subdivided. 1 = Subdivided by secondary, lateral septa (i.e., tripartite) (Ortmann, 1911: pl. 86, figs. 9-10b). 2 = Interlamellar septa effectively separated by a “marked swelling” (Ortmann, 1921: pl. 48, fig. 7b). Discussed in the text. Coded as “inapplicable” among taxa in which the interlamellar space of the marsupium is not divided into water-tubes. [LMD/4; G/30-31; GO/7-8; HBH/15-16; RH/30-31]

49. Relative number of transverse (primary) septa. — 0 = Greater in marsupial than in nonmarsupial regions of marsupial and in nonmarsupial demibranchs. 1 = Similar in marsupial and nonmarsupial regions of marsupial and in nonmarsupial demibranchs. Coding generally follows Hoeh et al. (2001; Roe & Hoeh, 2003); coded as “inapplicable” among taxa in which the interlamellar space of the marsupium is not divided into water-tubes. [HBH/13; RH/26-27]

50. Expansion of the marsupial demibranchs when gravid. — 0 = Not expanded; ventral edge remains sharp. 1 = Ventral mantle edge augmented with tissue to allow for expansion only laterally . 2 = Mantle capable of expansion ventrally as well as laterally; tissue may allow larvae to be released via the ventral margin. Among anodontine (Unionidae) mussels, the gravid demibranchs distend laterally, taking on the appearance of an inflated air mattress. The lampsiline marsupium is restricted to a portion of the demibranch. It is easily identifiable by its ventral extension and inflation. Ortmann (1910, 1912) observed that glochidia were forcibly expelled through the ventral margin of the lampsiline marsupium. [LMD/7; G/32-33, 35; GO/9-11; HBH/11; RH/22]

51. Spermatozuegmata. — 0 = Spermatozoa released separately. 1 = Spermatozoa released as part of a motile, acellular sphere (Lynn, 1994: fig. 1). Only those palaeoheterodonts for which observations exist were coded. All outgroup taxa were coded as releasing spermatozoa separately. This character has not been used in previous phylogenetic analyses of the Palaeoheterodonta.

52. Spermatozoa with multiple pro-acrosomal vesicles. — 0 = Absent. 1 = Present. Only palaeoheterodonts for which there are observations are coded as having spermatozoa with multiple pro-acrosomal vesicles, although these may fuse (or disappear) in the mature gamete (Healy, 1989, 1996; Rocha & Azevedo, 1990). [GW/155]

53. Doubly-uniparental inheritance of mitochondria. — 0 = Absent, mitochondrial inheritance strictly maternal. 1 = Present. Most palaeoheterodont species are coded as “missing data”. Observations come from Curole & Kocher (2002) and Hoeh et al. (2002). Discussed in the text. This character has not been used in previous phylogenetic analyses of the Palaeoheterodonta.

References to Other Life History Characters:
  • Curole, J.P. & T.D. Kocher. 2002. Ancient sex-specific extension of the cytochrome c oxidase II gene in bivalves and the fidelity of doubly-uniparental inheritance. Molecular and Biological Evolution 19: 1323-1328.
  • Graf, D.L. 1997. The effect of breeding period on the biogeography of freshwater mussels (Bivalvia: Unionoidea) in the Minnesota region of North America. Occasional Papers on Mollusks 5: 393-407.
  • Healy, J.M. 1989. Spermiogenesis and spermatozoa in the relict bivalve genus Neotrigonia: relevance to trigonioid relationships, particularly with Unionoidea. Marine Biology 103: 75-85.
  • Healy, J.M. 1996. Molluscan sperm ultrastructure: correlation with taxonomic units within the Gastropoda, Cephalopoda and Bivalvia. pp. 99-113. In: Taylor JD, ed. Origin and Evolutionary Radiation of the Mollusca. Oxford University Press, New York, New York.
  • Hoeh, W.R., D.T. Stewart & S.I. Guttman. 2002. High fidelity of mitochondrial genome transmission under the doubly uniparental mode of inheritance in freshwater mussels (Bivalvia: Unionoidea). Evolution 56: 2252-2261.
  • Lynn, J.W. 1994. The ultrastructure of the sperm and motile spermatozeugmata released from the freshwater mussel Anodonta grandis (Mollusca: Bivalvia: Unionidae). Canadian Journal of Zoology 72: 1452-1461., 1994
  • McMichael, D.F. & I.D. Hiscock. 1958. A monograph of freshwater mussels (Mollusca: Pelecypoda) of the Australian region. Australian Journal of Marine and Freshwater Research 9: 372-508.
  • Ortmann, A.E. 1910. The discharge of glochidia in the Unionidae. Nautilus 24: 94-95.
  • Ortmann, A.E. 1911. Monograph of the Najades of Pennsylvania. Part I. Anatomical investigations. Part II. The system of North American Najades. Memoirs of the Carnegie Museum 4: 279-347.
  • Ortmann, A.E. 1912. Notes upon the families and genera of the Najades. Annals of the Carnegie Museum 8: 222-365.
  • Ortmann, A.E. 1921. South American Naiades; a contribution to the knowledge of the freshwater mussels of South America. Memoirs of the Carnegie Museum 8: 451-670.
  • Rocha, E. & C. Azevedo. 1990. Ultrastructural study of the spermatogenesis of Anodonta cygnea L. (Bivalvia: Unionidae). Invertebrate Reproduction and Development 18: 1969-196.

 
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Page last updated 28 December 2007.