This species is easily recognised based on its brittle, very thinly valved (almost transparent) orange shell of up to 13 mm in length.
Lentidium dalyfluvialis Hallan & Willan, 2010
Infraclass Heteroconchia
Cohort Heterodonta
Megaorder Neoheterodontei
Order Myida
Superfamily Myoidea
Family Corbulidae
Subfamily: Lentidiinae
Genus Lentidium Cristofori & Jan, 1832 (Type species Lentidium maculatum Cristofori & Jan, 1832, = Lentidium mediterraneum Costa, 1830) (Synonyms Corbulomya Nyst, 1845; Dentina Megerle von Mühlfeld, 1841).
Original name: Lentidium dalyfluvialis Hallan & Willan, 2010. In Hallan, A. & Willan, R. C. (2010). Two new species of Lentidium (Myida: Corbulidae) from tropical northern Australia: remarkable fresh/fluviatile to brackish-water bivalves. Molluscan Research 30(3): 143-153.
Type locality: Browns Creek, Daly River, Northern Territory.
We follow the taxonomy of Hallan and Willan (2010). However, this species probably belongs to a new genus as it is quite distinct from any other corbulid.
This species is a shallow burrower in sandy sediments overlain with a thin layer of mud, where it commonly lies at an angle with its siphons exposed in the water column. For the family, L. dalyfluvialis is rather active and can readily reposition itself in the sediment when disturbed.
Commonly found in high densities of up to 1000 individuals/m2, in a narrow section of the upper estuarine, freshwater to slightly brackish parts of the Daly River, Northern Territory.
Endemic to the Daly River, Northern Territory.
Lentidium dalyfluvialis is the only species of this genus present in freshwater environments in Australia (and possibly world-wide). As far as is known, it is endemic to the Daly River, Northern Territory, where it occurs with other molluscs presumably endemic to that river, such as Colenuda kessneri and Coleglabra nordaustralis (both Clenchiellidae).
The congener Lentidium origolacus Hallan & Willan, 2010 was abundant in the lacustrine phases of the Gulf of Carpentaria during the Last Interglacial Period, primarily associated with low-salinity environmental conditions (see Chivas et al., 2001; Hallan and Willan, 2010; Hallan et al., 2012). Its extant population is known only from the Gilbert River (also in the Gulf), albeit the vast majority of this material was collected in the euryhaline lower reaches of the estuary (Hallan and Willan, 2010). The species has never been observed live, and it is unknown if it ventures into freshwater in the modern environment. While L. origolacus could have occurred in salinities approaching freshwater in the palaeo-lake, it is possible these occurrences consisted of short, intense and opportunistic blooms enabled by the opening of a niche habitat more so than favourable environmental conditions. As such, these Quaternary records cannot readily be used as proxies for present-day conditions in which the species may occur (Hallan, pers. obs.).
Chivas, A. R., García, A., van der Kaars, S., Couapel, M. J. J., Holt, S., Reeves, J. M., Wheeler, D. J., Switzer, A. D., Murray-Wallace, C. V., Banerjee, D., Price, D. N., Wang, S. X., Pearson, G., Edgar, T., Beaufort, L., De Deckker, P., Lawson, E. & Cecil, C. B. 2001. Sea-level and environmental changes since the last interglacial in the Gulf of Carpentaria, Australia: an overview. Quaternary International 83–85: 19–46.
Hallan, A. & Willan, R. C. (2010). Two new species of Lentidium (Myida: Corbulidae) from tropical northern Australia: remarkable fresh/fluviatile to brackish-water bivalves. Molluscan Research 30: 143.
Hallan, A., Colgan, D. J., Anderson, L. C., García, A. & Chivas, A. R. (2013). A single origin for the limnetic-euryhaline taxa in the Corbulidae (Bivalvia). Zoologica Scripta 42: 278-287.
Hallan, A., García, A., Chivas, A. R., & Devriendt, L. 2012. Molluscs from the Gulf of Carpentaria, Australia, throughout the Last Interglacial period (past ~130 ka). Quaternary International 279-280: 186.
Willan, E. C. & Kessner, V. (2021). A conspectus of the freshwater molluscs of the Daly River catchment, Northern Territory. Northern Territory Naturalist 30: 108-137.
