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Lortiella Iredale, 1934

Diagnostic features

Shell narrowly elongated (ratio of maximum height of shell to its length <45%) or ‘adze-shaped’ with a short, rounded anterior, straight ventral margin and obliquely truncated posterior margin. Valves winged. Periostracum colour light olive to dark brown or almost black in large specimens. Shell surfaces and beaks lack obvious sculpture. Pseudocardinal teeth lamellar and semi-serrated in small shells and either peg-like, or flattened, and smooth in larger shells. 

Marsupium formed in the inner demibranch.

Siphons pigmented with mottled patches, black and tan in colour, and had 2–4 rows of bulbous/pyramidal pale-coloured papillae on the inhalant siphon. Inhalant siphon ca. 1 times the size of the exhalant siphon.

Anatomy: The gills (ctenidia) are eulamellibranch and the foot is a compressed, tongue-shaped foot lacking a byssal groove. Larvae are brooded in a marsupium that occupies at least two thirds of the inner pair of demibranchs. Inhalant and exhalant siphons not prominent and formed by the mantle edge which is open ventrally, branchial 'siphon' larger than anal 'siphon'. Labial palps of medium size, elongate-triangular in shape.

The species of Lortiella can be distinguished as follows:

Lortiella rugata (Sowerby). Shell with reduced hingeposterior end squarely truncate, ventral margin straight to slightly concave, markedly elongate (ratio of maximum height of shell to its length >29-41%).

Lortiella froggatti Iredale. Shell with moderately strong hinge; posterior end rounded, obliquely truncate;  ventral margin convex, elongate (ratio of maximum height of shell to its length >40-55%), :

Lortiella opertanea Ponder & Bayer. Shell with rather reduced hinge; posterior end rounded, ventral margin straight to concave, obliquely truncate;  elongate (ratio of maximum height of shell to its length 36-45%),

The Australian genera of freshwater mussels are distinguished by the following shell characters (note that all are subject to erosion with age, depending on the local environment):-

Hyridella. Beak of young specimens at least sculptured with V-shaped ridges; shell quadrate to elongate (ratio of maximum height of shell to its length >50%), not markedly winged. Hinge strong with grooved pseudocardinal teeth and simple 'lateral' teeth. Shell surface (other than beaks) more-or-less smooth except for concentric growth lines.

Velesunio. Beaks smooth, shell can be rather thick, rounded in outline (ratio of maximum height of shell to its length >50%), often inflated, hinge lamellar, usually simple (rarely serrated). Shell surface with concentric growth lines only.

Alathyria. Shell typically large, elongate-ovate (ratio of maximum height of shell to its length >50%), often distinctly winged, thick, hinge usually with heavy, pseudocardinal teeth grooved, 'lateral' teeth smooth. Shell surface more-or-less smooth, with concentric growth lines only.

Cucumerunio. Shell very elongate (ratio of maximum height of shell to its length <40%), beaks sculptured with V-shaped ridges; rest of shell surface with conspicuous nodules or ridges. Hinge strong, pseudocardinal teeth grooved.

Lortiella. Shell elongate (ratio of maximum height of shell to its length <45%), winged posteriorly, hinge simple, not well developed. Beaks smooth and shell surface with concentric growth lines only. Found in NW Australia.

Westralunio. Shell more or less oblong (ratio of maximum height of shell to its length >50%). Pseudocardinal teeth erect, strongly serrated, shell small (less than 70 mm in length). Beaks smooth, shell rather thick, with concentric growth lines only. Restricted to SW Australia.

Classification

Class Bivalvia

Subclass Heteroconchia

Superorder Palaeoheterodonta

Order Unionida

Superfamily Unionoidea

Family Hyriidae

Subfamily: Velesunioninae

Genus Lortiella Iredale, 1934

Type species: Mycetopus rugatus Sowerby, 1868

Original reference: Iredale, T. (1934). The Freshwater mussels of Australia. Australian Zoologist 8: 57-78, plts 3-6.

Type locality: Victoria River, Northern Territory.

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

Rivers, streams and water catchment dams. Found along stream banks at the edge of the river in shallow burrows with the tips of the posterior ends of shells exposed, or under flat stones on the river bottom. Suspension feeders. Dioecious. Brood young in marsupia in the inner pair of demibranchs. Larvae (glochidia) parasitic, using fish as hosts and dispersal agents.

Distribution

Daly and Katherine Rivers, Northern Territory, to the De Grey River in the Pilbara region of Western Australia.

Notes

The shells of this genus are readily distinguished based on their characteristic shape.

Further reading

Graf, D. L., Jones, H. A., Geneva, A. J., Pfeiffer, J. M. III & Klunzinger, M. W. (2015). Molecular phylogenetic analysis supports a Gondwanan origin of the Hyriidae (Mollusca: Bivalvia: Unionida) and the paraphyly of Australasian taxa. Molecular Phylogenetics and Evolution. 85: 1-9.

Haas, F. (1969). Superfamilia Unionacea. Das Terreich, 88 (1-10), 1-663.

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

Iredale, T. (1943). A basic list of the fresh water Mollusca of Australia. Australian Zoologist 10: 188-230.

Klunzinger, M. W., Jones, H. A., Keleher, J., & Morgan, D. L. (2013). A new record of Lortiella froggatti Iredale, 1934 (Bivalvia: Unionoida: Hyriidae) from the Pilbara region, Western Australia, with notes on anatomy and geographic range.Records of the Western Australian Museum 28: 1-6.

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. 

Ponder, W. F. & Bayer, M. (2004). A new species of Lortiella (Mollusca: Bivalvia: Unionoidea: Hyriidae) from northern Australia. Molluscan Research 24: 89-102.

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.

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. (2004). A guide to the provisional identification of the freshwater mussels (Unionoida) of Australasia. Albury, Murray Darling Freshwater Research Centre.

Walker, K. F., Byrne, M., Hickey, C. W. & Roper, D. S. (2001). Freshwater Mussels (Hyriidae) of Australasia. Pp. 5-31 in G. Bauer & Wächtler, K. Ecology and Evolution of the Freshwater Mussels Unionoida. Ecological Studies. Berlin, Springer-Verlag.

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.