Both Sphaerium and Musculium have small shells (length up to 9 mm, usually 7-8 mm) with their beaks usually slightly shifted posteriorly, not protruding, prodissoconch sometimes separated by growth break line but never forming a bean-shaped cap. The ligament is externally visible, and elevated in the largest specimens. Siphons are short, especially their fused part, and the dorsal retractor muscles of the inhalant siphon are markedly reduced, and their scars merged with those of the posterior adductors. The kidney has a broad to narrow and elongate dorsal lobe. The outer demibranch is 30-40% the height of the inner demibranch (depending on stage of development) (based on Korniushin, 2000).
According to Korniushin (2002) the autapomorphies of Sphaerium are (1) interlamellar septae in inner demibranch are developed on all gill filaments and (2) and there is similtaneous development of several broods (asynchronous brooding) and the released juveniles have an outer demibranch present. In Musculium a cap is present on the umbo and the inner cardinal tooth on the left valve is straight. Sphaerinova differs from Sphaerium in having weak upper retractors of the branchial siphon.
Diagnosis of Sphaerium given by Bespalyala et al. (2024): Shell large-sized (shell length in adults varies between 6 and 25 mm), rounded to ovate in shape, typically thick walled.
The beaks rounded and slightly prominent or narrow, pore density varies among species. Cardinal and lateral teeth well developed. Nephridia moderately elongated. Two siphons (exhalant and inhalant) are present. The outer and inner demibranch relatively well developed.Sphaerium Scopoli, 1777
Infraclass Heteroconchia
Cohort Heterodonta
Megaorder Neoheterodontei
Order Sphaeriida
Superfamily Sphaerioidea
Family Sphaeriidae
Subfamily Sphaeriinae
Genus Sphaerium Scopoli, 1777
Type species: Tellina cornea Linnaeus, 1758. Europe.
Musculium Link, 1807
Type species: Tellina lacustris O. F. Müller, 1774. Europe.
Original reference: Link, D.H.F. (1807-1808). Beschreibung der Naturalien-Sammlung der Universität zu Rostock. Adlers Erben. 1 Abt. [Part 1], pp. 1-50; 2 Abt. [Part 2], pp. 51-100; 3 Abt. [Part 3], pp. 101-165; Abt. 4 [Part 4],pp. 1-30; Abt. 5 [Part 5], pp. 1-38 [1808]; Abt. 6 [Part 6], pp. 1-38., available online at https://www.biodiversitylibrary.org/page/43301237
The Australian species were included in Sphaerinova Iredale as a subgenus of Sphaerium (Kuiper 1983) or Musculium (Korniushin 2000) but Lee and Ó Foighil (2003) included only Sphaerium tasmanicum in the subgenus Sphaerinova and that taxon and Musculium were considered to be subgenera of Sphaerium. Graf & Cummings (2023) treat both Sphaerinova and Musculium as synonyms of Sphaerium (along with another 50 genus-group names!) but without justification.
The two subgenera of Sphaerium that are recognised here follows Bespalyala et al. (2024), although this author had doubts about the status of Musculium.
Inhabit almost all types of freshwater habitats including springs, rivers, lakes, ponds, billabongs, waterholes, small creeks, drains and peat bogs. Brood young in multiple brood pouches. Suspension and deposit feeder. Live in sediment and in weeds.
Australia, and taxa from New Zealand, USA, Spain, Portugal, eastern Europe and northern Asia.
Sphaerium is distinguished from the related genus Euglesa by its larger size, median or nearly median position of the umbo, presence of two tubular siphons, two pairs of retractor muscles by the lower (branchial) siphon, and the outer demibranchs have both descending and ascending lamellae and multiple brood pouches.
Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing.
Bespalaya, Y. V., Vinarski, M. V., Aksenova, O. V., Babushkin, E. S., Gofarov, M.Y., Kondakov, A. V., Konopleva, E. S., Kropotin, A. V., Mabrouki, Y., Ovchankova, N. B., Palatov, D. M., Sokolova, S. E., Shevchenko, O. V. T., Abdelkhaleq, F. T., Soboleva, A. A., Zubrii, N. A. & Bolotov, I. N. (2024). Phylogeny, taxonomy, and biogeography of the Sphaeriinae (Bivalvia: Sphaeriidae). Zoological Journal of the Linnean Society 201: 305-338.
Fuentealba-Jara, C., D’Elia, G., González, F. & Franco-Jaccard, C. (2017). Phylogenetic reconstruction of Sphaeriidae (Veneroida: Bivalvia) and phylogenetic position of Pisidium chilense. Hidrobiológica, 27: 115-117.
Lee, T. (2019). Sphaeriidae Deshayes, 1855 (1820). Pp. 197-201 in C. Lydeard & Cummings, K. S. Freshwater Mollusks of the World: a Distribution Atlas. Baltimore, John Hopkins University Press.
Korniushin, A. V. (2000). Review of the family Sphaeriidae (Mollusca: Bivalvia) of Australia, with the description of four new species. Records of the Australian Museum 52: 41-102.
Korniushin, A. V. & Glaubrecht, M. (2002). Morphological characters analysis, the intergroup phylogenetic relationships and possible outgroups of the family Sphaeriidae (Mollusca, Bivalvia). Vestbuj zoologii 36(4): 3-22.
Kuiper, J. G. J. (1983). The Sphaeriidae of Australia. Basteria 47: 3-52.
Lamprell, K. & Healy, J. (1998). Bivalves of Australia, volume 2. Leiden, Backhuys Publishers.
Lee, T. & Ó Foighil, D. (2003). Phylogenetic structure of the Sphaeriinae, a global clade of freshwater bivalve molluscs, inferred from nuclear (ITS-1) and mitochondrial (16S) ribosomal gene sequences. Zoological Journal of the Linnean Society 137: 245-260.
Smith, B. J. & Kershaw, R. C. (1979). Field guide to the non-marine Molluscs of South-eastern Australia. Canberra, A.N.U. Press.
Smith, B. J. & Kershaw, R. C. (1981). Tasmanian Land and Freshwater Molluscs. Hobart, University of Tasmania.
