Shells usually thin and fragile, medium-sized (usually 8–10 mm long). Umbos narrow central or slightly shifted posteriorly, prosogyrous (bent anteriorly), protruded, with clearly separated prodissoconch sometimes forming a bean-shaped cap. Hinge plate relatively narrow; tendency to hinge teeth reduction evident in many (but not all) species. Ligament not visible from exterior. Both siphons tubular. Upper (exhalant) siphon with one pair of retractor muscles, lower (inhalant) with two pairs. Siphons long, dorsal retractors of branchial siphon normally developed, with their scars well marked as appendages of posterior adductor scars or separated. Outer demibranch of two lamellae, relatively small (height about 1/3 inner demibranch height), begins at 5th filament of inner demibranch. Brood pouches multiple.
This species differs from native species in their large size (up to 11.5 mm in length), and distinct prosogyrous beaks bearing clearly separated prodissoconchs referred to as 'caps' by Korniushin (2000). The ligament is not visible externally (it is in Sphaerium (Sphaerinova) but, unlike Sphaerinova, the siphonal retractor muscles are well developed.
Sphaerium (Musculium) cf. lacustre (Müller, 1774)
Common name: Pea shell, pea clam, pill clam
Infraclass Heteroconchia
Cohort Heterodonta
Megaorder Neoheterodontei
Order Sphaeriida
Superfamily Sphaerioidea
Family Sphaeriidae
Subfamily Sphaeriinae
Type species: Tellina cornea Linnaeus, 1758. Europe.
Subgenus Musculium Link,1807 (Type species Tellina lacustris Müller, 1774) (Synonyms Calyculina Clessin, 1872; Cyclas (Phymesoda) Rafinesque, 1820).
Original name: Tellina lacustris Müller, 1774. In Müller, O. F. (1773-1774). Vermium terrestrium et fluviatilium, seu animalium infusoriorum, helminthicorum, et testaecorum, non marinorum, succincta historia. Vol. 1, Havniæ (Copenhagen) & Lipsiæ (Leipzig), Heineck & Faber.
Australian record: 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.
Type locality: Unknown.
M. lacustre is a protandric, simultaneous hermaphrodite - populations can contain two overlapping populations at any one time. Young are brooded in multiple brood pouches. Maturation can occur at 2 mm in size, however most become mature at 4-6mm. Suspension and deposit feeder.
Members of this group prefer temporary or unstable water bodies. Inhabit almost all types of freshwater habitats including springs, rivers, lakes, ponds, billabongs, waterholes, small creeks, drains and peat bogs. Lives in sediment and in weeds.
Introduced in eastern South Australia (in the vicinity of Adelaide).
Native distribution Europe. Also introduced to Hawaii.
First recorded in Australia by Korniushin (2000), however identification is tentative - similar to large European forms of M. lacustre particularly in the narrow, protruding umbos and the separated prodissoconch (cap).
Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing.
Heard, W. H., (1977). Reproduction of fingernail clam (Sphaeriidae: Sphaerium and Musculium). Malacologia 16(2): 421–455.
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.
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. (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.
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.
