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Xenostrobus securis (Lamarck, 1819)

Diagnostic features

Shell blue black to brown, elongate, interior of valves nacreous, umbones almost terminal, sculpture of growth linesPeriostracum smooth. Long internal ligament and well developed byssus; hinge teeth lacking. Juveniles with characteristic zig-zag markings.

Dioecious, gills filibranchPosterior adductor muscle much larger than anterior. Foot small and elongate.


Xenostrobus securis (Lamarck, 1819)

Common name: Axe Head Mussel; Pygmy Mussel

Class Bivalvia

Subclass Pteriomorphia

Order Mytilida

Superfamily Mytiloidea

Family Mytilidae

Genus Xenostrobus Wilson, 1967 (Type species: Volsella inconstans Dunker, 1856).

Original name: Modiola securis Lamarck, 1819. Lamarck, J. P. B. A. d M. C. d (1819). Histoire naturelle des animaux sans vertèbres, présentant les caractères généraux et particuliers de ces animaux, leur distribution, leurs classes, leurs familles, leurs genres, et la citation des principales espèces quis'y rapportent; précédée d'une introduction offrant la détermination des caractères essentiels de l'animal, sa distinction du végétal et des autres corps naturels, enfin, l'exposition des principes fondamentaux de la zoologie. Vol. 6 part 1. Deterville, Verdiere, Paris. pp. 1-343.

Type locality: “Nouvelle Hollande" and Timor. 

Synonyms: Limnoperna fortunei kikuchii Habe, 1981; Modiola fluviatilis Hutton, 1878; Modiola nitens Gould & Carpenter, 1857; Modiola vexillum Reeve, 1857; Perna confusa Angas, 1871.

Biology and ecology

Inhabits brackish water, lives on hard substrates in lower reaches of tidal creeks and rivers and upper reaches of bays, inlets and harbours often forming extensive colonies. Has a salinity tolerance range from about 30 parts per thousand of chlorine to about 1 part per thousand and is able to survive at the latter for many months, although adults remain inactive with their valves closed below about 2 parts per thousand (Wilson 1968).


Southern half of Australia; New Zealand; Introduced to the Italian part of the Adriatic Sea and the Mediterranean Sea in general; Spanish part of the North Atlantic Ocean and China (including Hong Kong) and Japan.


Recent genetic studies by Colgan and DaCosta (2013) have shown that there are different genetic forms of X. securis in Australia, one of which is invasive, the other not. They also found that Xenostrobus and the very similar Limnoperna are not congeneric, although that had been suggested by some authors.

Further reading

Colgan, D. J. & da Costa, P. (2013). Invasive and non-invasive lineages in Xenostrobus (Bivalvia: Mytilidae). Molluscan Research 33: 272-280.

Kimura, T., Tabe, M. & Shikano, Y. (1999). Limnoperna fortunei kikuchii Habe, 1981 (Bivalvia: Mytilidae) is a synonym of Xenostrobus securis (Lamarck, 1819): introduction into Japan from Australia and/or New Zealand. Venus 58: 101-117.

Ng, T.H., Tan, S.K., Wong, W.H., Meier, R., Chan, S-Y., Tan, H.H. and Yeo, D.C.J. 2016. Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLOS One. DOI:10.1371/journal.pone.0161130.

Pascual, S., Villalba, A., Abollo, E., Garci, M., González, A.F., Nombela, M., Posada, D. & Guerra, A., (2010). The mussel Xenostrobus securis: a well-established alien invader in the Ria de Vigo (Spain, NE Atlantic).Biological Invasions 12:.2091-2103.

Ponder, W. F., Clark, S. A. & Dallwitz, M. J. (2000). Freshwater and estuarine molluscs: an interactive, illustrated key for New South Wales. Melbourne, CSIRO Publishing.

Wilson, B. R. (1967). A new generic name for three recent and one fossil species of Mytilidae (Mollusca: Bivalvia) in southern Australasia with re-descriptions of the species. Proceedings of the Malacological Society of London 37: 279–295.

Wilson, B. R. (1968). Survival and reproduction of the mussel Xenostrobus securis (Lam.) (Mollusca: Bivalvia: Mytilidae) in a Western Australian estuary: Part I. Salinity tolerance.Journal of Natural History 2: 307-328.

Wilson, B. R. (1969). Survival and reproduction of the mussel Xenostrobus securis (Lamarck) (Mollusca; Bivalvia; Mytilidae) in a Western Australian estuary. Pt. II: Reproduction, growth and longevity. Journal of natural History 3:  93-120.