Harrisonina Freeman

Description

Introduction

Small larvae, up to 4 mm long.

Antenna

Antenna with 5 segments; basal about 1.2 times length of flagellum; no segments ringed, segment 3 shorter than 4, 5th distinct, equal in length to 3rd. Blade extending to subapex of antenna. Lauterborn organs not visible; style extending to mid 4th segment.

Labrum

Labrum with SI possibly absent (not visible to Brundin 1966 or on any specimen available); SII and III simple, slender, approximated to each other; SIV small pegs. Spinulae reduced to 2, short. Labral lamellae absent Pecten epipharyngis consisting of 5 scales. Premandible apically broad with indistinct apical tooth. Ungula squat.

Mandible

Mandible with broad base and narrow apical toothed section, with 4 clearly delimited inner teeth; apical tooth not much longer than any inner teeth. Seta subdentalis short.

Mentum

Mentum with large, protruding paired median teeth, and 8 pairs of lateral teeth; 1st laterals may have lateral notch, and distinct small appressed tooth. Ventromental plate narrow. Setae submenti closer to mentum base than to occipital margin.

Maxilla

Maxilla with strong medially directed brush on labial margin. Palp short, squat. Hypopharynx with 3 brushes, median strong, laterals weaker.

Body

With anterior and posterior parapods separate, each bearing an apical crown of claws; posterior parapods long and slender. Procercus well developed, sub-quadrate; 5-6 anal setae present. Body setae pale and indistinct.

Notes

Taxonomic Notes

Harrisonina petricola, the sole species in the genus, was stated by Brundin to be a very peculiar chironomid based largely upon the unusual pupal leg sheath arrangement in the pupa (all leg sheaths directed straight backwards, reaching far beyond the wing sheaths, Brundin 1966: fig. 620). Although Freeman (1956) had described the genus as an orthoclad, Brundin placed the taxon in the Diamesinae but without specifying which features allowed this placement. Unpublished molecular data (Cranston et al., in prep) confirms Brundin's placement, despite the lack of annulation in the larval antenna, and the reduced hypopharyngeal brush typical of diamesines.

Amongst the diamesines, Harrisonina is distinctive by its non-setose body very squat procercus with 6 strong anal setae, by the presumed absence of SI seta and the approximated and subequal SII and SIII setae, with short hypopharyngeal brush.

This genus is keyed also as an orthoclad, as it might be using the subfamily key.

Ecological Notes

The immature stages and adults of Harrisonina petricola were found by Professor A. D. Harrison breeding in the thin film of water running over the stones in a temporary mountain stream in Olifants River Valley, Transvaal, South Africa. According to Brundin (1966) the species was found also near Salisbury in Southern Rhodesia (Harare / Zimbabwe) (Harrison 1965, p. 392). Cranston (unpublished) found the larvae and pupae in a newly flowing creek near Komga in the Eastern Cape in November.

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