Afrochlus Freeman

Description

Introduction

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

Antenna

Small, less than 20% of head capsule length, non-retractile; 5-segmented, apex of segment 2 and all of 3 annulate, segments poorly differentiated from each other 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. Antennal ratio ca. 0.5.

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 strong dark scales. Premandible absent.

Mandible

With modest-sized subapically tooth, longer apical tooth and 3 inner teeth, the innermost of which is clearly 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 3 median teeth and 5 pairs of lateral teeth. Median teeth subequal, lateral teeth diminishing in an even slope except for very small 2nd laterals. Ventromental plate weakly present, visible in uncompressed menta. 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 interconnecting fine claws, and separate crowns of serrate claws. Spiracles present dorsally on abdominal segment VIII. Procercus uniformly dark, somewhat conical, about as high as the basal width, with fine lateral seta, bearing apically 6 short dark setae. Posterior parapods well developed, with dark, simple claws of 2 distinct sizes, subapical ring of small claws, apical crown of long claws.

Notes

Taxonomic Notes

The larva resembles that of Archaeochlus, distinguished only by the unicolourous dark procerci.

Ecological Notes

Afrochlus harrisoni is known only from the type locality, Ngoma Kuriru, Zimbabwe. In the original description, Freeman (1964) noted Harrison’s report of the species being sluggish and crawling in grass of small swamps from which very small streams arise in the rainy season. We can confirm part of this behaviour, having observed hundreds of adult females crawling over the substrate, including grasses and the exposed rock surfaces. However, the insects were very active (on a warm day) and moved with a rapid zig-zag motion, with wings beating but without taking flight. We observed no males at the site, yet pupal exuvial evidence showed a 1:1 sex ratio. Males emerged from pupae that were collected at the same time as female pupae were present and adult females were active. It is possible that there is progyny, with our visit taking place just at the onset of male emergence. On the other hand the males may be less active, awaiting contact with the active female. Timing of A. harrisoni development appears to be identical to that of the putative sister group Archaeochlus, in which developing larvae are found in temporary streams soon after seasonal rains inundate the vegetated soil on rock outcrops. On Ngoma Kuriru, Harrison collected female adults one month after the onset of the rains, and in the summer of 1996, the first rains had fallen in mid-November, some two weeks before our visit.

The behaviour of the immature stages of A. harrisoni very closely resembled that of Archaeochlus species in Africa and Australia, with larvae aggregated in shallow films of water running from the capping or vegetated soil on rock outcrops. Larvae of A. harrisoni were found in some numbers up to twenty metres below the sources of the seepage streams and in small pools formed in depressions of the granite within the course of the flowing water. Larvae generally appeared to keep their posterior spiracles at the water surface, though this was not so for those living in the pools. Pupae were free living in similar habitats to the larvae and were capable of some movement to attain the water surface in pools. Although the species is known only from the type locality, this is unlikely to represent a restricted distribution. Granite doualas (outcrops) similar to Ngoma Kuriru can be seen from the summit, extending far to the north and east, appearing to provide suitable habitat across a wide area.

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