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Hyridella depressa (Lamarck, 1819)

Diagnostic features

This species is more elongate (maximum height relative to maximum length about 50%) than the other species of Hyridella, and the postero-dorsal margin is angled and the dorsal margin anterior to the beaks slopes away markedly while it is flatter in the other species. The beak sculpture is fine, as in H. drapeta.


Hyridella depressa (Lamarck, 1819)

Common name: Freshwater mussel

Class Bivalvia

Subclass Heteroconchia

Superorder Palaeoheterodonta

Order Unionida

Superfamily Unionoidea

Family Hyriidae

Subfamily: Hyriinae

Genus Hyridella Swainson, 1840

Original name: Unio depressa Lamarck, 1819. Lamarck, J.B.P.A. (1819). Histoire Naturelle des Animaux sans Vertèbres.  Paris : J.B.P. Lamarck Vol. 6 (1) 2nd Edn 343 pp. 

Type locality: Nepean River, near Sydney, New South Wales.

Synonyms: Propehyridella nepeanensis novata Iredale, 1943; Unio mutabilis Lea, 1859; Unio paramattensis Lea, 1862. Rugoshyria depressa monticola Iredale, 1934; Rugoshyria depressa vicinalis Iredale, 1934; Rugoshyria depressa bega Iredale, 1943; Rugoshyria depressa lowanna Iredale, 1943.

State of taxonomy

The last major taxonomic revision of Australian freshwater mussels was by McMichael and Hiscock (1958).

Based on the available molecular results, Walker et al. (2014) pointed out that a re-assessment of Australian hyriids is needed.

Biology and ecology

Shallow burrower in silty sand/mud in streams and rivers, including small mountain streams in flowing water. Suspension feeder. Larvae are brooded in the gills and are parasitic on fish. It is the most common species in coastal rivers and streams (except for Hunter and Shoalhaven Rivers) and does not occur in billabongs.

Additional information on the biology and ecology of members of this family can be found in Fauna of Australia, vol. 5A, p. 296-298.


Coastal rivers and streams of coastal southeast Queensland, New South Wales (although absent from the Hunter and Shoalhaven Rivers) and eastern Victoria and in most areas in this range is the most common freshwater mussel (H. Jones, pers. comm.). 

Further reading

Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing.

Byrne, M. (1998). Reproduction of river and lake populations of Hyridella depressa (Unionacea: Hyriidae) in New South Wales: implications for their conservation. Hydrobiologia 389: 29-43.

Byrne, M. and Vesk, P.A. 1996. Microanalysis of the elements in granules in Hyridella depressa (Bivalvia): multivariate analysis and biomonitoring potential. Australian Journal of Ecotoxicology 2:91-97.  

Cotton, B.C. & Gabriel, C.J. (1932). Australian Unionidae. Proceedings of the Royal Society of Victoria (ns) 44: 155-160.

Haas, F. (1912). Die Unioniden. pp. 113-136 in Küster, H.C., Martini, F.W. & Chemnitz, J.H. (eds) Systematiches Conchylien-Cabinet.  Nürnberg : Bauer & Raspe Bd 9 Abt. 2.

Iredale, T. (1934). The freshwater mussels of Australia. Australian Zoologist 8: 57-78 pls 3-6.

Jeffree, R. A., Markich, S. J. & Brown, P. L. (1993). Comparative accumulation of alkaline-earth metals by two freshwater mussel species from the Nepean River, Australia: consistences and a resolved paradox. Marine and Freshwater Research 44: 609-634.

Johnson, R. I. & Baker, H. B. (1973). The types of Unionacea (Mollusca: Bivalvia) in the Academy of Natural Sciences of Philadelphia. Proceedings of the Academy of Natural Sciences of Philadelphia 125: 145-186.

Jones, H. A. & Byrne, M. (2014). Changes in the distributions of freshwater mussels (Unionoida: Hyriidae) in coastal southeastern Australia and implications for their conservation status. Aquatic Conservation: Marine and Freshwater Ecosystems 24: 203-217.

Jones, H. A., Simpson, R. D. & Humphrey, C. L. (1986). The reproductive cycles and glochidia of fresh-water mussels (Bivalvia: Hyriidae) of the Macleay River, Northern New South Wales, Australia. Malacologia 27: 185-202.

Jupiter, S. D. & Byrne, M. (1997). Light and scanning electron microscopy of the embryos and glochidia larvae of the Australian freshwater bivalve Hyridella depressa (Hyriidae). Invertebrate Reproduction and Development 32: 177-186.

Smith, B. J. (1992). Non-marine Mollusca. Pp. i-xii, 1-408 in W. W. K. Houston. Zoological Catalogue of Australia, 8. Canberra, Australian Government Publishing Service.

Smith, B. J. & Kershaw, R. C. (1979). Field guide to the non-marine Molluscs of South-eastern Australia. Canberra, A.N.U. Press.

Lamprell, K. & Healy, J. (1998). Bivalves of Australia, volume 2. Leiden, Backhuys Publishers.

McMichael, D. F. & Hiscock, I. D. (1958). A monograph of the freshwater mussels (Mollusca: Pelecypoda) of the Australian region. Australian Journal of Marine and Freshwater Research 9: 372-508 + 319 plates.

Shea, M. 1995. Freshwater molluscs of Sydney. Australian Shell News 88:4- 6.

Walker, K. F. (1981). The distribution of freshwater mussels (Mollusca: Pelecypoda) in the Australian zoogeographic region. Pp. 1233-1249 in A. Keast. Ecological Biogeography of Australia. The Hague, Dr W. Junk.

Walker, K. F., Jones, H. A. &  Klunzinger, M. W. (2014). Bivalves in a bottleneck: taxonomy, phylogeography and conservation of freshwater mussels (Bivalvia: Unionoida) in Australasia. Hydrobiologia 735:61–79.