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Musculium (Musculium) cf. lacustre (Muller, 1774)

Diagnostic features

Shells usually thin and fragile, medium-sized (usually 8–10 mm long). Umbones 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 Sphaerinova) and, unlike Sphaerinova, the siphonal retractor muscles are well developed.

Classification

Musculium (Musculium) cf. lacustre (Muller, 1774)

Common name: Pea shell

Class Bivalvia

Subclass Heteroconcha

Superorder Heterodonta

Order Cardiida

Superfamily Sphaeroidea

Family Sphaeriidae

Genus Musculium Link,1807

Subgenus Musculium (= Calyculina Clessin, 1872;  Cyclas (Phymesoda) Rafinesque, 1820).

Original name: Tellina lacustris Müller, 1774. 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.

Biology and ecology

M. lacustre is a protandric, simultaneous hermaphrodite - populations can contain two overstepping populations at any one time.Maturation can occur at 2 mm in size, however most become mature at 4-6mm. Can occur in drainage ditches.

Member 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. Brood young in multiple brood pouches.

Distribution

Introduced in eastern South Australia (in the vicinity of Adelaide).

Native distribution Europe. Also introduced to Hawaii.

Notes

First recorded in Australia by Korniushin (2000), however identification is tentative - similar to large European forms of M. lacustre particularly in the narrow protruding umbone and the separated prodissoconch (cap).

Further reading

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.

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