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Jarrah Forest Freshwater Snail (Glacidorbis occidentalis)

The Jarrah Forest Freshwater Snail is a minute freshwater snail recorded in south-western Western Australia, especially in intermittent forest streams. It also occurs at a vegetated ephemeral claypan. Careful checks of stream and wetland habitats are important during site works. In WA, it is in DBCA Priority 3, a priority category.

Conservation status

Western Australia, WA Threatened and Priority Fauna List: Priority 3.

Seasonal activity

Adults oversummer in the stream bed and emerge shortly after the first winter flows. Brooded young appear to be released during winter. Calendar months and a detailed seasonal survey window are unknown.

Winter: Brooded young appear to be released as veligers during winter; adults emerge shortly after the first winter flows.

Summer: Adults oversummer in the stream bed.

The numeric month field does not encode a calendar month mapping, so seasonal timing is stated in the notes rather than assigned to specific months.

  • Winter flows: Emergence is reported shortly after the first winter flows, and young appear to be released during winter. Calendar months are not specified.
  • Summer: Adults are reported to oversummer in the stream bed; exact months are not specified.
  • Site survey planning: Planning window only. Schedule habitat checks around site conditions and proposed works; no complete survey season or calendar months have been established.

Identification: Appearance and size

This is a very small freshwater snail. Reliable identification may require specialist examination.

The shell is smooth, with evenly convex whorls and fine growth lines. Adult size is reported as 1 to 1.3 mm, and the diagnostic account gives a maximum diameter of up to 1.2 mm.

The species is distinguished from other Glacidorbis by the narrow base of its central radular teeth. This is not a practical feature to check in the field.

Identification: Similar species and field signs

Other minute freshwater snails may be mistaken for this species. No field comparison with other local snail species has been published.

A tiny smooth shell may prompt further investigation, but shell appearance alone may not confirm the identification. Record the location and habitat and seek specialist advice for confirmation.

Distribution: Known range

The known range is in south-western Western Australia, including forest streams in the northern jarrah forest.

The species is reported from south-western WA, south of Perth, and from streams throughout the northern jarrah forest. It is reported not to occur in lowland rivers west of the Darling Range.

Atlas of Living Australia records show 20 WA records at seven distinct 0.1-degree locations, between latitudes -34.5 and -31.4 and longitudes 116 and 116.7. Records outside WA were excluded as likely errors.

Distribution: WA regions and named records

The DBCA regions are Swan and South West. Named records or localities include Wugong Brook near Jarrahdale, Julimar claypan, Kangaroo Gully and Drummond Nature Reserve.

Habitat: Forest streams

Intermittently flowing forest streams are the best-described habitat. The species has also been recorded at a vegetated ephemeral claypan.

The species is largely restricted to forest streams with intermittent flow. It has been described from small intermittent streams, including gravel riffle sections, in south-western WA.

Habitat: Claypan record

The species was recorded during an aquatic invertebrate survey at Julimar claypan, a small, shallow, fresh and ephemeral wetland in wandoo woodland. How commonly it uses claypans compared with streams is unknown.

Foraging habitat: Reported diet

The snail’s diet is tentative, and its feeding locations and behaviour are unknown.

The snail is presumed to feed on small injured animals, such as insect larvae and other molluscs. This diet has not been confirmed.

Foraging habitat: Foraging areas

No particular feeding microhabitat or foraging behaviour has been documented. Do not infer a feeding site from the diet description alone.

Breeding habitat: Reproduction

The species has brooded young, with apparent release during winter. Breeding biology is otherwise poorly known.

The species produces brooded young which appear to be released as veligers during winter. Clutch or brood size and further details of development are unknown.

Breeding habitat: Breeding habitat

No separate breeding habitat has been documented. The species is associated with intermittently flowing forest streams, but no specific breeding microhabitat is known.

Sheltering habitat: Summer refuge

The stream bed is the only reported sheltering or seasonal refuge habitat.

Adults oversummer in the stream bed. Their exact position in the bed and the materials they use for shelter are unknown.

Sheltering habitat: Other shelter

No other sheltering habitat has been documented. Avoid assuming that dry stream-bed material is unoccupied, particularly before winter flows return.

Threats: Known pressures

No species-specific threats have been documented.

No species-specific threats, population trend or evidence of imminent decline have been documented. The species is poorly known and known from several locations.

Threats: Work-site precaution

As a precaution, treat occupied or potentially suitable stream and wetland habitat as sensitive to disturbance. This is a risk-management measure, not a claim that a particular impact has been documented for this species.

Survey methodology: 1. Desktop assessment

No species-specific survey protocol or detection rate has been established. The snail’s minute size calls for careful, habitat-focused searches.

Check available records and map intermittent streams, gravel riffles, vegetated ephemeral claypans and connected wet areas in the works footprint and nearby area. Confirm whether known records or suitable habitats may be affected.

Survey methodology: 2. Field inspection

Inspect suitable stream and wetland areas carefully, including accessible gravel riffles and stream-bed material. Because the snail is only about a millimetre across, use close visual inspection and suitable magnification as general practice when searching for minute aquatic snails.

Record the date, flow or wetness conditions, habitat, search area and any specimens or signs. Avoid damaging or removing habitat unnecessarily.

Survey methodology: 3. Identification and records

A tiny shell alone does not confirm the identification. Seek a freshwater mollusc specialist where confirmation is needed, and retain location and habitat information with any record.

Vegetation associations: Woodland

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

The species was recorded during an aquatic invertebrate survey at Julimar claypan, a small, shallow, fresh and ephemeral wetland in wandoo woodland.

Automatically indexed from existing profile text. Not a verified preference, mapped occurrence or habitat requirement. Check the original source and regional qualifiers before use.

Evidence: Unreviewed profile-derived candidate

Confidence: Not independently verified

Region: Scope as described in the quoted profile text; not independently verified. Profile states: WA.

Habitat use: general

Attribution gap: No sentence-level reference is attached to the original profile block. Review the profile bibliography; this candidate is not source-verified.

Vegetation associations: Wetland or sedgeland

The species was recorded during an aquatic invertebrate survey at Julimar claypan, a small, shallow, fresh and ephemeral wetland in wandoo woodland.

Automatically indexed from existing profile text. Not a verified preference, mapped occurrence or habitat requirement. Check the original source and regional qualifiers before use.

Evidence: Unreviewed profile-derived candidate

Confidence: Not independently verified

Region: Scope as described in the quoted profile text; not independently verified. Profile states: WA.

Habitat use: general

Attribution gap: No sentence-level reference is attached to the original profile block. Review the profile bibliography; this candidate is not source-verified.

Ecosystem associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific ecosystem association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Soil and substrate associations: Clay soils

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

It also occurs at a vegetated ephemeral claypan.

Automatically indexed from existing profile text. Not a verified preference, mapped occurrence or habitat requirement. Check the original source and regional qualifiers before use.

Evidence: Unreviewed profile-derived candidate

Confidence: Not independently verified

Region: Scope as described in the quoted profile text; not independently verified. Profile states: WA.

Habitat use: general

Attribution gap: No sentence-level reference is attached to the original profile block. Review the profile bibliography; this candidate is not source-verified.

Water and wetland associations: Water-associated habitat mentioned in profile

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

The species is largely restricted to forest streams with intermittent flow.

Automatically indexed from existing profile text. Not a verified preference, mapped occurrence or habitat requirement. Check the original source and regional qualifiers before use.

Evidence: Unreviewed profile-derived candidate

Confidence: Not independently verified

Region: Scope as described in the quoted profile text; not independently verified. Profile states: WA.

Habitat use: general

Attribution gap: No sentence-level reference is attached to the original profile block. Review the profile bibliography; this candidate is not source-verified.

Fauna records and mapped habitat: Not yet analysed

Record locations can be overlaid with mapping, but record frequency alone does not measure habitat preference. No species is excluded from desktop assessments by this analysis.

No quality-controlled record-to-map analysis has been completed for this species. The existing generalised distribution dots and indicative range polygons have not been treated as precise occurrence coordinates.

A defensible run needs dated, independently attributable records, coordinate uncertainty, duplicate and captive-record checks, layer versions and regional scope. Preference and absence require additional survey-effort and detection evidence.

Habitat limitations and contrary evidence: No supported exclusion recorded

Not recorded is not the same as cannot occur. Low suitability, resident habitat, breeding habitat and occasional movement are different conclusions.

This library has not established a vegetation, ecosystem or soil-type exclusion for this species. This does not mean all habitat is suitable; the evidence needed to justify an exclusion has not been assembled.

Habitat limitations and contrary evidence: Before using a negative association

  • Confirm the taxon, geographic region, life stage and habitat function covered by the evidence.
  • Check survey methods, season, repeated effort and detectability before interpreting non-detection.
  • Investigate credible contradictory records and microhabitats absent from broad mapping.
  • Do not convert a missing map class, low record count or failed data request into species absence.

Before habitat disturbance: 1. Map and assess

Plan works to identify and avoid stream and wetland habitat before clearing or ground disturbance begins.

Review known records and inspect the proposed disturbance area for intermittent forest streams, gravel riffles, stream beds and vegetated ephemeral wetlands. Include areas that may be affected indirectly by works.

Before habitat disturbance: 2. Set precautions

Where suitable habitat is present, obtain ecological advice on the need for targeted searches and establish clear no-go or low-impact areas before works. Brief crews on the snail’s very small size and the possibility that it may be overlooked.

During habitat disturbance: 1. Control the work area

Keep disturbance away from stream and wetland habitats wherever practicable, and respond cautiously to unexpected finds.

Keep vehicles, stockpiles and ground disturbance within approved boundaries. Avoid unnecessary disturbance of stream beds, riffles and wetland margins, and follow site controls intended to prevent sediment or other material entering aquatic habitat.

During habitat disturbance: 2. Respond to a find

If a suspected specimen is found, pause work in the immediate area, protect the habitat from further disturbance and contact the project ecologist or fauna spotter catcher for identification and advice. Do not relocate snails or alter the stream bed without an approved direction.

After habitat disturbance: 1. Check the site

After works, check that habitat protection measures remain in place and document any observations.

Inspect affected work areas and nearby stream or wetland habitat for unauthorised disturbance, sediment movement or damage to agreed exclusion areas. Escalate concerns to the project ecologist.

After habitat disturbance: 2. Record outcomes

Document survey effort, conditions, habitat observations, suspected or confirmed records, and any incidents. No species-specific post-disturbance monitoring period or protocol has been established, so agree any follow-up with the project ecologist and relevant approvals.

Rehabilitation actions: 1. Restore habitat carefully

Rehabilitation should protect the form and function of affected stream and wetland habitat without assuming unrecorded species requirements.

Use the approved rehabilitation plan to stabilise disturbed areas and avoid unnecessary changes to stream beds, riffles and wetland margins. No species-specific planting or substrate prescription has been established.

Rehabilitation actions: 2. Review recovery

Check that rehabilitation has not created further disturbance to aquatic habitat and record any follow-up observations. Seek ecological advice if works have altered a known or potentially occupied site.

Sources