Opponobranchia

Nucinella surugana, copyright G. & Ph. Poppe.

Belongs within: Bivalvia.
Contains: Nuculidae, Solemya.

The Solemyoida: a taste for sulphur
Published 4 June 2019
Atlantic awning clam Solemya velum, copyright Guus Roeselers.

The small bivalves that make up the Solemyoida were long a mystery, ecology-wise. Though they have a long history, potentially going back as far as the Ordovician (Cope 2000), they are not known to have ever been diverse, and only just over fifty species are known from the modern fauna. Living solemyoids are divided between two very distinct families that probably diverged near the origin of the group. The Solemyidae, awning clams, have relatively long shells that gape at each end, no teeth in the dorsal hinge, and tend to have an unusually thick periostracum (the overlying layer of horny proteinaceous matter that covers the outside of the mineral shell). They generally live in burrows buried deep in sediment. The Nucinellidae are a group of minute clams with an average length of about half a centimetre that are mostly found in deep waters, generally not buried quite so deep in the mud as the awning clams. They have a less elongate shell than the Solemyidae that does not gape and simple peg-like teeth in the hinge. What the two families do share is a markedly reduced gut and feeding appendages that initially caused much speculation about what exactly they were feeding on.

Nucinella sp. with foot extended, from Taylor & Glover (2010). Scale bar equals 1 mm.

The answer, as it turns out, was that they were not exactly ‘feeding’ on much, if anything. Solemyoids have relatively large gills that provide a comfortable living place for sulphur-oxidising bacteria, sheltered from the outside world while the host clam keeps up a continuous flow of water through its burrow from above the sediment surface. In return, the bacteria fix hydrogen sulphide rising from the underlying mud to provide both themselves and their host with nutrients. In this way, solemyoids have largely been able to get by without actively eating for close to 450 million years, achieving something the likes of Jasmuheen can only dream of.

Systematics of Solemyoida
<==OpponobranchiaPC11
    |--+--Ctenodontidae [Ctenodontoidea]M96
    |  |    |--Praectenodonta raricostaeBRW98
    |  |    |--TancrediopsisJB12
    |  |    |    |--T. delicatula Sherrard 1959F71
    |  |    |    `--T. minuta Sherrard 1959F71
    |  |    `--CtenodontaSV03
    |  |         |--*C. nasutaC04
    |  |         |--C. famatinensis Harrington 1938SB93
    |  |         `--C. iruyensis (Harrington 1938)SB93
    |  `--NuculoideaBRW98
    |       |--NuculidaeGW02
    |       |--PristiglomidaeBRW98
    |       |--ThoraliaSB93 [ThoraliidaeBRW98]
    |       |    `--T. languedociana (Thoral 1935)SB93
    |       `--PraenuculidaeBRW98
    |            |--LedopsisJB12
    |            |--NuculodontaJB12
    |            `--DeceptrixC04
    |                 |--D. carinata Fuchs 1919SB93
    |                 `--D. levataC96
    `--Solemyoida [Lipodonta, Palaeobranchia, Solemyoidea]GW02
         |--SolemyidaeSB93
         |    |--SolemyaGW02
         |    |--Psiloconcha senecta (Sardeson 1896)SB93
         |    |--AdulomyaBRW98
         |    |--DystactellaSB93
         |    |    |--D. aedilis (Eichwald 1856)SB93
         |    |    `--D. ordovicicus (Pojeta & Runnegar 1985)SB93
         |    |--JaneiaBRW98
         |    |    |--J. parallela (Beede & Rogers 1899) [=Solemya (Janeia) parallela]ZP86
         |    |    |--J. primaeva (Phillips 1836) [=Solemya (Janeia) primaeva]ZP86
         |    |    `--J. siluricaBRW98
         |    `--Acharax Dall 1908BRW98, AJH07
         |         |--A. agassiziBRW98
         |         |--A. cretacea Kanie & Nishida 2000AJH07
         |         `--A. eremitaBRW98
         `--Manzanellidae [Nucinellidae]AJH07
              |--Cyrilla dalliBRW98
              |--Manzanella Girty 1909AJH07
              |    `--M. elliptica Girty 1909SB93
              |--Huxleya Adams 1860AJH07
              |    |--H. cavernicola Hayami & Kase 1993AJH07
              |    |--H. decussata Adams 1862AJH07
              |    |--H. ochiaiensis (Chinzei 1959)AJH07
              |    `--H. sulcata Adams 1860AJH07
              `--Nucinella Wood 1851AJH07
                   |--*N. miliaris [=Nucula miliaris]P61
                   |--N. adamsi (Dall 1889)AJH07
                   |--N. alleni Vokes 1966AJH07
                   |--N. boucheti La Perna 2005AJH07
                   |--N. concentricaBRW98
                   |--N. gigantea Amano, Jenkins & Hikida 2007AJH07
                   |--N. glabrata Stoliczka 1871AJH07
                   |--N. kanekoi Matsukuma, Okutani & Tsuchi 1982AJH07
                   |--N. liasinaSB93
                   |--N. maorianus (Hedley 1904)P61
                   |--N. maxima (Thiele & Jackel 1931)AJH07
                   |--N. oregona (Vokes 1956)AJH07
                   |--N. seguenzae (Dall 1898)AJH07
                   |--N. serrei Lamy 1912AJH07
                   |--N. sohli Pojeta 1988AJH07
                   |--N. surugana Matsukuma, Okutani & Tsuchi 1982AJH07
                   |--N. viridis Matsukuma, Okutani & Tsuchi 1982AJH07
                   `--N. viridulaBRW98

*Type species of generic name indicated

References

[AJH07] Amano, K., R. G. Jenkins & Y. Hikida. 2007. A new gigantic Nucinella (Bivalvia: Solemyoida) from the Cretaceous cold-seep deposit in Hokkaido, northern Japan. Veliger 49 (2): 84–90.

[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.

[C96] Cope, J. C. W. 1996. The early evolution of the Bivalvia. In: Taylor, J. D. (ed.) Origin and Evolutionary Radiation of the Mollusca pp. 361–370. Oxford University Press: Oxford.

Cope, J. C. W. 2000. A new look at early bivalve phylogeny. In: Harper, E. M., J. D. Taylor & J. A. Crame (eds) The Evolutionary Biology of the Bivalvia pp. 81–95. The Geological Society: London.

[C04] Cope, J. C. W. 2004. Bivalve and rostroconch mollusks. In: Webby, B. D., F. Paris, M. L. Droser & I. G. Percival (eds) The Great Ordovician Biodiversification Event pp. 196–208. Columbia University Press.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[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.

[JB12] Johnson, M. E., & B. G. Baarli. 2012. Development of intertidal biotas through Phanerozoic time. In: Talent, J. A. (ed.) Earth and Life: Global biodiversity, extinction intervals and biogeographic perturbations through time pp. 63–128. Springer.

[M96] Morton, B. 1996. The evolutionary history of the Bivalvia. In: Taylor, J. D. (ed.) Origin and Evolutionary Radiation of the Mollusca pp. 337–359. Oxford University Press: Oxford.

[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.

[P61] Powell, A. W. B. 1961. Shells of New Zealand: An illustrated handbook 4th ed. Whitcombe and Tombs Limited: Christchurch.

[SV03] Sánchez, T. M., & N. E. Vaccari. 2003. Ucumariidae new family (Bivalvia, Anomalodesmata) and other bivalves from the Early Ordovician (Tremadocian) of northwestern Argentina. Ameghiniana 40 (3): 415–424.

[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.

[ZP86] Zhang, R., & J. Pojeta Jr. 1986. New bivalves from the Datang Stage, Lower Carboniferous, Guangdong Province, China. Journal of Paleontology 60 (3): 669–679.

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