Australopelopia Cranston

Description

Introduction

Medium-sized larvae, up to 7 mm long. golden-yellow with cephalic margin darker golden-brown to darker brown; mandible golden, tip brown, ligula golden brown basally, darker in distal half. Capsule longish-oval, cephalic index 0.7-0.75. Cephalic setation: SSm, V9 and V10 aligned at 45° to antero-ventral axis, VP posterior to V10, dorsal pit present, S7 close to S8.

Antenna

Antenna 0.5 head length, AR: 3.6-3.7; basal segment c15 times as long as basal width, Ring organ distal to mid-point (60%); second segment annulate. Blade bifid, broad outer branch slightly shorter than thin 75-80 inner branch. Lauterborn organs small, style extending to apex of antenna.

Mandible

Mandible gently curved, with rather parallel-sided apical tooth; long seta subdentalis arises between triangular accessory tooth and well developed, apically directed basal tooth, both protruding beyond inner contour of mandible. Ventrolateral setae closely approximated outer margin, separated from sensillum minusculum by same distance as posteriormost seta 3.

Maxilla

Maxilla with strong ring organ situated in mid-segment of palp, with well-developed crown of setae and sensilla including 3-segmented b-seta with each section subequal in length.

Body

Body without a fringe of swim setae. Anal tubules slender, shorter than half length of posterior parapod, tapering apically, about 4x as long as basally wide. Procercus about 3x as long as wide, with 7 anal setae. Subbasal seta of posterior parapod simple. Posterior parapods with 15-16 simple short and triangular to long and narrow claws subtended by area of fine spinules on subapical parapod. Anterior parapod claws fine and pale, posterior claws broader, simple, golden-yellow.

Notes

Taxonomic Notes

Australopelopia runs to couplet 26 in Wiederholm (1983) in which the only mutually exclusive feature requires assessment of the relative size - "large" vs "without large" - of the "basal mandibular tooth"". There is uncertainty about whether the structure in question is indeed a basal tooth, or just an extension of the mola around the site of insertion of the seta interna. However, accepting that the basal tooth is large, then the outwardly curved inner teeth of the ligula and simple parapod claws lead to Pentaneura Philippi or Telopelopia Roback. It resembles the latter more in having shorter anal tubules and procerci, non-linear, coarsely granulate pseudoradula, but differing in the shape of the muscle attachment area. Alternatively, if it is considered to lack a large basal mandibular tooth, then subsequently an irreconcilable combination of features is encountered - although the ring organ of the palp lies in the middle third (admittedly at the anterior end), the pseudoradula does not link to any sclerotised area, and the pecten hypopharyngis teeth are homogeneous in size, precluding identity with Trissopelopia or Hudsonimyia. The alternative couplet would lead to some Thienemannimyia-series genera, none of which have as strongly developed inner/basal mandibular teeth as the taxon under consideration.

The aforementioned key does not take into account the taxonomically valuable feature of the relative positions of the cephalic setae and sensory pores whose intra-generic invariance and inter-generic diagnostic value was recognised by Kowalyk (1985). Notable amongst these are the ventral cephalic setae S9, S10, Seta submenti (SSm) and the ventral pit (VP) which alone can distinguish amongst Australian taxa of Pentaneurini (Cranston, 1996). Following Kowalyk's key for Pentaneurini possessing a simple basal palp segment and concave ligula (couplet 14 onward), the approximation of S7 and S8, and presence of a dorsal pit leads to Telopelopia and the Thienemannimyia-series. The alignment of S10, antero-lateral to S9, essentially precludes Pentaneura from consideration (Pentaneura sp., Kowalyk, 1985: Figs. 140, 141; Pentaneura inconspicua, P. ? cinerea, Cranston pers. obs.).

Ecological Notes

Australopelopia prionoptera is distributed on the eastern margin of Australia, from Cape Tribulation in northern Queensland to northern Tasmania, predominantly in shaded streams. The single record from Western Australia is from the extreme southwest of the state from a shaded stream that harbours several other cool stenothermic taxa of gondwanan affinities. The larva, typically for the tribe Pentaneurini, is predatory with a diet that includes chironomid larva little smaller than its own length, and includes earlier instars of its own species. As assessed by a year-long periodic interception of floating pupal exuviae, A. prionoptera adults, although few in number, emerged only in a narrow period of mid-summer in a south-eastern subalpine stream. Serendipitous 24 hr drift net collections suggest that this seasonality is artifactual. Final instar larvae can be found throughout winter, exuviae can be collected at almost any time of year, and larvae returned to the laboratory can pupate from within a few days to as much as several months later. This phenomenon appears independent of feeding (usually a pupation stimulus to Tanypodinae larvae) or of temperature, and it may be that there is a partial, perhaps facultative diapause in this species.This taxon originally was thought to represent an Australian Pentaneura, and was argued to represent a relictual gondwanan distribution, but the postulated phylogenetic position as sister group to a broad Thienemannimyia-group undermines this historical speculation. The Thienemannimyia-group is almost worldwide, and its internal phylogenetic relationships are unknown: even some generic delimitation is suspect. Furthermore the Patagonian and New Zealand Tanypodinae are poorly known.

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