Draft:Fluvidona petterdi

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Fluvidona petterdi
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Superfamily:	Rissooidea
Family:	Tateidae
Genus:	Fluvidona
Species:	F. petterdi
Binomial name
Fluvidona petterdi (Smith, 1882)

Fluvidona petterdi is a species of minute freshwater snail in the family Tateidae, endemic to southeastern Australia. It is known only from spring-fed streams and headwaters, and has been the subject of recent taxonomic and conservation assessments due to its restricted range and sensitivity to habitat alteration. Fluvidona petterdi is a tiny freshwater snail belonging to the family Tateidae (Smith, 1882) endemic to spring-fed headwaters of northern New South Wales and southern Queensland, Australia. It was first described by Edgar A. Smith in 1882. The species lives in cool (15–18 °C), well-oxygenated streams with fine gravel and detrital substrate and feeds on periphytic algae and plays a role in nutrient cycling (Miller, Ponder, & Clark, 1999; Ponder, Colgan, Terzis, Clark, & Miller, 1996). Its minimal range and specialized habitat requirements suit groundwater extraction, land use change, and climate-driven hydrological change (Dudgeon & Strayer, 2025; Mukherjee et al., 2023).

Taxonomy and nomenclature

The species was first described by Edgar A. Smith in 1882 under the name Hydrobia petterdi. It was later transferred to the genus Fluvidona by Miller, Ponder and Clark in 1999. Smith (1882) originally described shell morphology from specimens collected near the Clarence River headwaters, where Smith (1882) described the species as Hydrobia petterdi. Miller et al. (1999) transferred it to the genus Fluvidona (now accepted by MolluscaBase and the Australian Faunal Directory), a name erected (by Shannon, 1927) for species D. australis, D. lauta, and D. rufilineata, an improbable display of trinarism (Miller & Wells, 1985, p. 505), another fruit of the injudicious use of the name Daciqua by Reynolds. The current hierarchical classification is: The family Tateidae is defined by the group of species assigned to the genus Fluvidona, with Fluvidona petterdi (Miler et al., 1999) as the type species. In the past, it was known as Hydrobia petterdi Smith (1882); alternatively, it was also misidentified under Victoria (Smith, 1882; Miller et al., 1999). Miller et al. (1999) distinguish Fluvidona from related tateids by a broadly conical shape of the shell, a truncated aperture, and a reduced operculum. F. petterdi has a high spired shell with 5–6 whorls, smooth growth lines, and an adult shell height of 3.5 mm (Ponder et al., 1996). The molecular barcoding of the COI gene confirmed its distinct lineage in Fluvidona, removed early confusion with sympatric hydrobiids (Ponder et al., 1996). Subspecies no (Winterbourn, 2021). Current classification follows MolluscaBase and the Australian Faunal Directory:

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Gastropoda
• Superfamily: Rissooidea
• Family: Tateidae
• Genus: Fluvidona
• Species: F. petterdi

Synonyms:

• Hydrobia petterdi Smith, 1882.

Distribution and habitat

Fluvidona petterdi is known exclusively from a handful of spring-fed creeks in northern New South Wales and southern Queensland. Specimens have been recorded at elevations between 200–350 m above sea level in headwater springs with cool (15–18 °C), well-oxygenated water. Substrate descriptions note fine gravel and coarse sand, often under dense riparian vegetation. Fluvidona petterdi is known from fewer than ten discrete spring complexes in an area of approximately 150 square kilometers in northern New South Wales and southern Queensland (Ponder et al., 1996). The species occurs in perennial, spring-fed streams emerging from sandstone aquifers in the 200–350 m elevation range above sea level in all known populations (Atlas Of Living Australia, 2025). These springs are stable springs with year-round flows, buffering of seasonal drought (Ponder et al., 1996). It is a substratum consisting of a mix of fine gravel, sand, and organic detritus overlaid by biofilms of diatoms and green algae (Mann, 1988). At occupied sites, water chemistry is pH 6.8–7.4, dissolved oxygen > 8 mg/L, and very low conductivity (< 150 µS/cm) indicative of little pollution (Atlas of Living Australia, 2025). Historical surveys (1990s– 2000s) show 100 to 250 individuals/m² on preferred microhabitat (under stones, wood); the surveys conducted more recently at some of these sites recorded no representatives of this species, interpreted as local extirpations (Ponder et al., 1996). Habitat fragmentation is severe: These springs sit on private agricultural land, backed up with cleared paddocks, many modified through stock watering or pumping bores (Mukherjee et al., 2023). Microhabitat selection is finely tuned: They both, juveniles and adults, avoid silty depositional zones and high flow bedrock areas and prefer intermediate flow, with a ~0.1–0.3 m/s speed, sustaining algal biofilms without scour (Ponder et al., 1996). Dewatering events lasting months, in which their absence of live snails, absence of recolonization, and significant cases of prolonged drawdowns due to groundwater extraction or drought (Dudgeon & Strayer, 2025), have all been linked.

File:Distribution map of Fluvidona petterdi.png

Distribution of F. petterdi in Australia

Ecology and behaviour

Members of the genus Fluvidona are grazers, feeding primarily on periphytic algae and detritus scraped from submerged surfaces using a radula. Although specific studies on F. petterdi feeding are lacking, closely related species exhibit similar trophic habits. Reproduction in Tateidae is oviparous, with eggs laid on submerged vegetation; juveniles emerge as miniature adults without a free-swimming larval stage. No captive-breeding data exist for F. petterdi, but field observations suggest a breeding season in spring (September–November). F. petterdi is a micrograzer that uses a rhipidoglossan radula typical of Tateidae, feeding on periphytic algae, bacteria, and detritus (Mann, 1988). Strong, Gargominy, Ponder, & Bouchet, 2008). Diatoms (Navicula, Nitzschia) and filamentous green algae (Cladophora) are dominant items of these related species' diets, and likely represent components of F. petterdi's diet as well (Strong et al., 2008). In the genus, ~ 5–12 lecithotrophic eggs are deposited in capsules attached to submerged substrates. They hatch as crawl-away snails, skipping the planktonic stage (Winterbourn, 2021). Although there is no available direct data for F. petterdi, congeners have a hatching period of 14–21 days, produce clutches in spring–autumn (≥ 16 °C), and live in captivity for 12–18 months (Winterbourn, 2021). The seasonal activity peaks in spring (September–November) and autumn (March–May), and is related to medium flows and steady temperatures; Individuals retreat into interstitial spaces and go inactive during high flows or sediment pulses until conditions are back to normal (Ponder et al., 1996). After prolonged dewatering and sediment smothering after upstream land clearing, mass mortality has been documented (Mukherjee et al., 2023). F. petterdi help to meet nutrient needs in the riparian zone (Mann, 1988) and prey upon odonate nymphs, amphipods, and small fish in downstream reaches (Mann, 1988). The limited dispersal capacity strongly structures genes. F_ST > 0.4 between spring populations according to preliminary allozyme data with negligible gene flow and cryptic speciation (Ponder et al., 1996).

Conservation status and threats

The species has not yet been assessed by the IUCN Red List and is currently unlisted under Australia's EPBC Act. However, its extremely restricted distribution and specialized habitat make it vulnerable. Potential threats include groundwater extraction, agricultural runoff, and alteration of spring hydrology. No targeted conservation programs are currently in place, though some spring habitats fall within protected reserves. Further surveys are recommended to clarify population trends and formal threat status. F. petterdi is currently unassessed on the IUCN Red List, or listed in Australia's EPBC Act or state threatened species schedules (EPBC Act database, 2025). However, its extent of occurrence (< 20,000 km²), severe fragmentation, and declining habitat place it in the Vulnerable or Endangered category of IUCN criterion B (Dudgeon & Strayer, 2025). Although recent resurveys do not relocate populations at two historical springs, the overall scenario is one of declining populations (Ponder et al., 1996). Hydrological monitoring and riparian revegetation, establishment of no-pump buffer zones, and in situ captive breeding trials as a starting point for future translocations are recommended (Dudgeon & Strayer, 2025). Finally, it suggests engagement of landholders via citizen-science water-quality monitoring to improve detection and stewardship (Mukherjee et al., 2023).

Morphological description

At 2.8-3.5 mm high and 1.8-2.2 mm wide, its shell is the most narrowly conical of its genus and among the largest (Ponder et al., 1996). It has 5–6 slightly convex whorls, a glossy amber brown periostracum, and a protoconch of 1.5 whorls with faint spiral striations under SEM (Miller et al., 1999). Fine growth lines (10–12 per mm) implicate slow deposition (Ponder et al., 1996). The aperture is thin, continuous, with the ovate–truncate aperture occupying ~ ⅓ of the shell height. A paucispiral operculum that fits tightly when retracted (Miller et al., 1999). It is pale gray on the soft body. Two pairs of tentacles are borne on the head, the upper with basal eyes and the lower for chemosensation (Winterbourn, 2021). Dissections show a vascularized mantle roof adapted for aquatic respiration (Winterbourn, 2021). It has rhipidoglossan radula, a single central tooth, five laterals, and many marginal cusps robust for scraping biofilm (Strong et al., 2008). A looped kidney is appropriate for ion-poor spring water, and a granular digestive gland for energy storage during low flow (Mann, 1988). Sexual dimorphism is subtle: They have a penile sheath and prostatic gland in males and an oviduct gland and uterine brood chamber in females (Winterbourn, 2021). Affixed to substrates, Eggs (~ 0.5 mm in size). This has not been observed in situ (i.e., on the river) (Winterbourn, 2021).

Evolutionary relationships

Phylogenetic analyses based on mitochondrial COI and nuclear 28S place F. petterdi in a southeastern Australian hydrobiid clade, which diversified during the aridification of the Miocene.Pliocene (Ponder et al., 1996). It is split from F. knoxi, which is estimated by molecular clock to be 5–7 Ma, in step with uplifting of the Great Dividing Range, and the origin of spring habitats (Ponder et al., 1996). Within Fluvidona, two lineages emerge: It includes a "inland-basin" clade (F. haltheri, F. lubra) and a "north-coastal" clade (F. petterdi, F. clemens, F. gariepinus)—all of which reflect the distribution of five of six clades of F. ushakensis (Miller et al., 1999), and reflect geographic barriers. Unfortunately, no active broadcast has continued yet. Multiple spring clades have converged on elongation and narrow apertures as shell traits, probably adaptive to the same set of predators and flow regimes. F. petterdi is thought to exhibit a constant steeper spire angle and thicker walls in the wider-stream relatives than in other, narrower, stream relatives through morphometric comparisons (Miller et al., 1999). Fluvidona-type shells at Pleistocene fossil springs at Dalhousie Springs indicate persistence in groundwater refugia (Ponder et al., 1996). Range contractions in glacial maxima and post-glacial re-expansions with little secondary contact and introgression have been indicated by phylogeographic reconstructions. Phylogenomic work with ultraconserved elements is in progress and aims to resolve deeper tateidae relationships and test for parallel spring adaptation. Defining cryptic diversity within F. petterdi will help define conservation units and management efforts (Miller et al., 1999).