Tridacninae

Belongs within: Cardiidae.

The Tridacninae, giant clams, are medium-sized to gigantic bivalves with radially ribbed shells, adapted for life among coral reefs.

Characters (Beesley et al. 1998): Shell large, thick to extremely thick, equivalve, exhibiting prominent ribs, sometimes with scales or short spines, a hinge of two oblique lamellar cardinal teeth and one or more lateral teeth (usually no anterior lateral teeth), and often a byssal gape. Microstructure aragonitic, with crossed-lamellar outer layer and complex crossed-lamellar inner layer. Ligament completely external, positioned posteriorly. Muscle scars principally associated with large posterior adductor muscle and posterior pedal retractor muscle. Pallial line simple, without pallial sinus. Hinge orientated ventrally against substratum, internal organs repositioned to accommodate specialised positioning of mantle and siphons dorsally. Greatly hypertrophied siphonal tissue adjoining outer edges of shell valves orientated dorsally. Inner and outer demibranchs of the gill narrow, curved (J- or S-shaped), filaments showing distinct nodes. Mouth anteriorly situated mouth; labial palps elongate, variably developed; Type V stomach; style sac unified to midgut; heart ventricle penetrated by elongate rectum; anterior adductor muscle absent; byssal and incurrent siphonal orifices positioned posteriorly; kidney elongate.

<==Tridacninae [Tridacnacea, Tridacnae, Tridacnidae, Tridacnoidea]S02
    |--Avicularium aviculare (Lamarck 1805)SB93
    |--ByssocardiumBRW98
    |--GoniocardiumBRW98
    |--HippopusGW02
    |    |--H. hippopus (Linnaeus 1758)H09 [=Chama hippopusH09, Tridacna (Hippopus) hippopusG20]
    |    |--H. maculatusH04
    |    `--H. porcellanus Rosewater 1982BRW98
    `--TridacnaS02
         |  i. s.: T. elongata Lamarck 1819H09
         |         T. lamarcki Hidalgo 1903H09
         |         T. rosewateriBRW98
         |         T. tevoroaS02
         |--T. (Tridacna) gigas (Linnaeus 1758)BRW98, H09 [=Chama gigasH09]
         `--T. (Chametrachea)BRW98
              |  i. s.: T. (Chametrachea) crocea (Lamarck 1819)SB93
              |--T. (C.) squamosa Lamarck 1819BRW98, PC11, BW09
              `--+--T. (Persikima) derasa Bolten 1798BRW98, PC11, H09 [=Tridachnes derasaH09]
                 `--T. (C.) maxima (Röding 1798)BRW98, PC11, BW09

*Type species of generic name indicated

References

[BRW98] Beesley, P. L., G. J. B. Ross & A. Wells (eds) 1998. Fauna of Australia vol. 5. Mollusca: The Southern Synthesis. Part A. Australian Biological Resources Study: Canberra.

[BW09] Bryce, C. & C. Whisson. 2009. The macromolluscs of Mermaid (Rowley Shoals), Scott and Seringapatam Reefs, Western Australia. Records of the Western Australian Museum Supplement 77: 177–208.

[GW02] 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 (4): 271–324.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

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

[PC11] Plazzi, F., A. Ceregato, M. Taviani & M. Passamonti. 2011. A molecular phylogeny of bivalve mollusks: ancient radiations and divergences as revealed by mitochondrial genes. PLoS One 6 (11): e27147.

[S02] Schneider, J. A. 2002. Phylogeny of cardiid bivalves (cockles and giant clams): revision of the Cardiinae and the importance of fossils in explaining disjunct biogeographical distributions. Zoological Journal of the Linnean Society 136: 321–369.

[SB93] Skelton, P. W., & M. J. Benton. 1993. Mollusca: Rostroconchia, Scaphopoda and Bivalvia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 237–263. Chapman & Hall: London.