Austrochlus Cranston

Description

Introduction

Up to 7 mm long, pale green with mid- to dark brown head capsule with much darker mentum, mandible and occipital margin; strongly sclerotised subgenal margin. Eye spot single, compact, somewhat quadrate.

Antenna

Well developed, about 1/3 head capsule length, non-retractile; 5 segmented, segments 2 always and 3 sometimes annulate, poorly differentiated but with both style and peg sensillum indicating apex of 2nd segment; blade subequal to segments 2-5 combined, accessory blade shorter than blade, apex of segment 1 also with small sensillum; without Lauterborn organs.

Labrum

Frontoclypeal apotome present. SI, SII and SIII elongate and enlarged, somewhat sickle-shaped in lateral view, arising from distinct pedestals; SIVa rod-shaped, arising from pedestal, SIVb rod-shaped. Few simple chaetae, seta premandibularis and labral rod present. Pecten epipharyngis of 5 scales. Premandible absent.

Mandible

With a small subapical tooth, longer apical tooth and 3-4 inner teeth, the innermost of which is variably separated from the mola. Seta subdentalis arising from ventral surface of mola, simple, short; seta interna arising from dorsal surface of mandible, with up to 25 simple branches.

Mentum

With three median teeth (ventromentum) and 7 pairs of lateral teeth (dorsomentum). Median teeth subequal, lateral teeth diminishing in an even slope except for very small 2nd laterals. Ventromental plate not detectable. Setae submenti close to outer posterior margin of mentum.

Maxilla

Palp short, with all setae and sensilla short, with long chaetulae. Few serrate galear lamellae, without pecten galearis. Chaetae numerous, long and simple, with broader weakly serrate anterior lacinial chaeta. Appendix absent.

Body

Anterior parapods fused basally, with separate crown of serrate claws. Spiracles present dorsally on abdominal segment VIII. Procercus darker pigmented posteriorly, somewhat conical, about as high as the basal width, with or without fine lateral seta, bearing apically 4 or 6-8 short setae. Posterior parapods well developed, with dark, simple claws of two distinct sizes - smaller in subapical ring.

Notes

Taxonomic Notes

Archaeochlus and Austrochlus larvae can be distinguished by the presence of distinct and functional posterior spiracles, rather squat hyaline and dark procerci bearing apically no more than 8 setae, and mentum with 6-7 pairs of lateral teeth and non-recessed middle tooth. Afrochlus larvae are similar but have a unicoloured dark procercus. Austrochlus larvae are distinguished only by their restriction to Australia. Archaeochlus is South African. This diagnosis is based on the description of Archaeochlus in Cranston et al. (1987).

Keys

Species of Austrochlus

    • 1. Procercus bearing more than 4 apical setae ... parabrundini
    • -- Procercus bearing only 4 apical setae ... 2
    • 2. Procercal setae longer than 210 µm ... austrocentralis
    • -- Procercal setae shorter than 210 µm long ... brundini

Ecological Notes

Austrocladius species share an unusual ecology with their relatives Afrochlus and Archaeochlus (as now restricted to southern African species). Larvae develop in short-lived waters flowing on exposed rocks, usually around and immediately below a seepage that allows ephemeral rainfall to persist for long enough (maximally a few weeks) for immature development to be completed. Typical habitats in central/western Western Australia are on granite rocks with some capping vegetation, ranging in size from Mount Augustus to exposures of less than half a hectare. Excepting the population of putative A. parabrundini at Mount Augustus, A. brundini and A. parabrundini are extensively sympatric, within core ranges with a northern limit at Mt Wittenoom (27º26’N), most southerly for A. brundini at 32º40’S, A. parabrundini at 32.39S with both at 32º34’S, with most westerly sites at 115º51’E, and with Hospital Rocks (120º07’E) providing the most easterly record.

The major predictor of Austrochlus (brundini and parabrundini) presence was rainfall in the wettest quarter, with rocks lacking any Austrochlus lying in a wetter range. This validates Edward’s observations of absence in the higher rainfall areas of (southern) Western Australia, with greater rainfall leading to longer-lasting flow and the absence of Austrochlus. Predicted potential outside the verified range included much of eastern WA, western Nullabor plain (which actually lacks suitable elevated microhabitat) and the mountain ranges of central Australia. Ground-truthing survey by Cranston revealed that Austrochlus indeed was present in suitable rocks following erratic winter rainfall in the James and East MacDonnell Ranges. This observation suggests that the isolation of a central Australian population (A. centralaustralis) took place without ecoclimatic (ecological) differentiation, and thus likely to have been in allopatry, by vicariance.

Although these bioclimatic predictions appear validated, evidently there may be another factor - the age of the rocks. Austrochlus are restricted to exposures of rocks of at least Jurassic age, and appear unable to colonise areas once past marine inundation have eliminated them. Apparent absence from climatically-predicted presence and suitable geography in the Gawler Ranges (South Australia) may be failure to recolonise after sea-level induced extinction.

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