Westralunio is distinguished from other hyriid genera in having a pseudocardinal tooth in right valve that is usually coarsely serrated, thick, and erect, fitting into deeply grooved socket in the left valve.
Anatomy: the gills (ctenidia) are of the eulamellibranch type, and the foot is compressed, tongue-shaped, and lacks a byssal groove. Larvae (glochidia) are brooded in a marsupium that occupies about two thirds of the inner pair of demibranchs of ctenidia. A supra-anal opening is absent. Inhalant and exhalant siphons are not prominent but protrude slightly beyond the shell margin and are formed by the mantle edge, which is open ventrally, separated from each other by a mantle bridge. The exhalant (branchial) 'siphon' is about 1.5 times larger than the inhalant (anal) 'siphon', with two to three rows of papillae. Siphons are heavily pigmented with orange and dark brown to black blotches. Labial palps are relatively small and semi-lunar in shape.
Westralunio is more distantly related to other hyriids than any other hyriid genus (Graf et al. 2015; Klunzinger et al. 2022).
The Australian taxa of Westralunio can be separated as follows:
W. carteri: From Klunzinger et al. (2022): “Specimens of W. carteri are distinguished from other Australian Westralunio taxa by having shell series that are significantly larger and more elongated than W. inbisi inbisi, but not different from W. inbisi meridiemus. The species has 10 diagnostic nucleotides at COI (57 G, 117 T, 210 G, 249 T, 255 C, 345 G, 423 T, 447 T, 465 A, 499 T) and 13 at 16S (137 T, 155 C, 228 C, 229 T, 60 G, 290 A, 305 G, 307 T, 310 A, 311 C, 321 T, 330 A, 460 A), which differentiate it from its sister taxa, W. inbisi inbisi and W. inbisi meridiemus using ASAP and TCS species delimitation models.” Maximum shell length rarely exceeds 100 mm. The distributional range of this species extends from the Moore-Hill Catchment in the north to the Margaret River catchment in the south, found primarily in westerly flowing streams, rivers and lakes flowing into the Indian Ocean within 150 km of the coast of south-western Australia.
W. inbisi inbisi: From Klunzinger et al. (2022): “Specimens of W. inbisi inbisi are distinguished from other Australian Westralunio taxa by having shell series that are significantly smaller and less elongated than W. carteri, but not W. inbisi meridiemus. The subspecies has three diagnostic nucleotides at COI (75 A, 87 T, 318 T) and none at 16S, which differentiate it from its sister taxa, W. carteri and W. inbisi meridiemus using ASAP and TCS species delimitation models.” Maximum shell length rarely exceeds 90 mm. The distributional range of this subspecies extends from Margaret and Blackwood Rivers in the west to Waychinicup River in the east, found primarily in southerly flowing streams, rivers and lakes flowing into the Southern Ocean within 100 km of the coast of south-western Australia.
W. inbisi meridiemus: From Klunzinger et al. (2022): “Specimens of W. inbisi meridiemus have five diagnostic nucleotides at COI (69 C, 123 C, 126 T, 483 A, 526 A) and none at 16S, which differentiate it from its sister taxa, W. carteri and W. inbisi inbisi using ASAP and TCS species delimitation models.” Maximum shell length rarely exceeds 90 mm. This subspecies is restricted to Margaret and Blackwood Rivers of south-western Australia.
Infraclass Heteroconchia
Cohort Palaeoheterodonta
Order Unionida
Superfamily Unionoidea
Family Hyriidae
Subfamily Velesunioninae
Genus Westralunio Iredale, 1934
Type species: Westralunio ambiguus carteri Iredale, 1934
Original reference: Iredale, T. (1934). The freshwater mussels of Australia. Australian Zoologist 8: 57-78 pls 3-6.
Type locality: Victoria Reservoir, Darling Range, 12 miles east of Perth, Western Australia.
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 reassessment of Australian hyriids is needed.
In addition to W. carteri, Klunzinger et al. (2022) described two additional subspecies of Westralunio from Australia. Under the taxonomic framework of McMichael and Hiscock (1958), two species of Westralunio (W. albertisi and W. flyensis) are found in Papua New Guinea, but unpublished preliminary genetic analysis suggests they may not belong in the same genus as their Australian sister taxa.
This genus favours slower flowing areas of freshwater rivers and streams and occurs in water supply reservoirs, farm dams, lakes and some wetlands. Infaunal, living two thirds to almost fully buried in sand and mud sediment. They are suspension feeders. Sexes are separate; females brood young in marsupia in the inner pair of demibranchs of ctenidia. Larvae (glochidia) are parasitic, using fish as hosts and dispersal agents.
Coastal rivers of south-western Australia. The genus also occurs in Papua New Guinea.
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 and umbo of at least young specimens 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, but sculpturing extends over shell surface in H. glenelgensis.
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%), usually 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 medium-sized (usually less than 70-80 mm in length, up to 90-100 mm). Beaks sculptured in un-eroded juveniles with v- or w-shaped ridges, shell rather thick, with collabral growth lines. Three taxa in SW Australia and two species in Papua New Guinea.
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