Philorheithridae Mosely

Weaver, John S., Gibon, François-Marie & Chvojka, Pavel, 2008, A new genus of Philorheithridae (Trichoptera) from Madagascar, Zootaxa 1825, pp. 18-28 : 18-19

Philorheithridae Mosely

The philorheithrids are a relatively small family, represented by eight described genera, six from Australasian Region ( Philorheithrus Hare , Aphilorheithrus Mosely , Tasmanthrus Mosely , Austrheithrus Mosely & Kimmins , Kosrheithrus Mosely & Kimmins , Ramiheithrus Neboiss ), and two from the temperate Neotropical Region ( Psilopsyche Ulmer and Mystacopsyche Schmid ). The new genus described herein, is the first philorheithrid recorded from the Afrotropical Region. The characteristics of the family have been described by Mosely & Kimmins (1953), Schmid (1955), and Neboiss (1977, 1991). Males and females have been described for all genera except Ramiheithrus , for which females are unknown.

Diagnosis. We agree with Parker and Wiggins (1987) that the Philorheithridae are closely related to the Odontoceridae . Adults of both families have unique modifications in the anterior wings, having a slender vein along the posterior margin, but we are not certain that it is a true vein. It was observed in Philorheithridae and Odontoceridae by Schmid (1964, 1980) and referred to it as the "post anale" vein. The anterior wing is also modified by having the posterior margin slightly recessed and the anal lobe small but conspicuously thickened. All of these characters together would appear to increase the strength of the posterior margin. This characteristic appears to be a strong synapormorphy, supporting monophyly of the Philorheithridae and Odontoceridae .

Reliable characteristics that may distinguish the Philorheithridae and the Odontoceridae from each other are not apparent to us at this time. A more through study of each group would be required to answer this question, and so the following diagnosis is tentative. Most of the Philorheithridae differ from the Odontoceridae by having 1) pronotum with median and lateral setal warts present (not fused together as they appear to be in Odontoceridae ); 2) adult male and female maxillary palps each with first segment bearing an apicomesal nodule; 3) anterior wings each with venation more complete, having forks 1, 2, 3, 5 usually present in males, and forks 1–5 in females; 4) anterior wings each with apical margin between forks 3 and 5, and posterior margin slightly concave; 5) anterior wings each with prominent basal lobe of posterior margin covered with numerous microtrichia on the upper surface; and 6) female genitalia with lateral appendages reduced.

Adult. Ocelli absent. Maxillary palps 5–segmented, except 4–segmented in males of Tasmanthrus , and 3– segmented in Austrheithrus . Five genera ( Philorheithrus , Aphilorheithrus , Tasmanthrus , Kosrheithrus , and Mystacopsyche ) unique among Trichoptera in having pair of pilifers arising ventrally from male frons ( Mosely & Kimmins 1953; Schmid 1955). Fore, middle, and hind leg spur formula is 2, 4, 4. R1 joins R2 apically in anterior wings of males and females except for Afrorheithrus ; length of 1A usually atrophied in most genera except Philorheithrus and Afrorheithrus ; and jugal lobe reduced. Secondary sexual dimorphism expressed in venation of anterior wings; male with forks 1, 2, 3, and 5; females with forks 1–5, except fork 4 absent in Kosrheithrus . Posterior wings of males and females with forks 1, 2, 5 present, except fork 3 also present in females of Aphilorheithrus . Abdominal sternite V with scent gland inconspicuous, apparently absent. A midsternal process is present on abdominal segment VI and/or VII in males and females of most genera.

A description of crypsis by the adult of Philorheithrus agilis was given by Hudson (1904) in the original species description:

"It delights to rest on overhanging twigs, situated close to the most rapid–running water. While thus

resting it is extremely difficult to see, the antennae being placed close together and thrust straight in

front of the insect, whilst the wings are closely folded around the body. When in this position the

creature must resemble a small stick, but if it be too closely approached it dashes with amazing rapid-

ity into the water, floats down the stream for a considerable distance, and eventually seizes hold of

some similar twig at the water=s edge, where it reposes as before. These peculiar habits are no doubt

protective, and certainly render both the detection and capture of the insect a most difficult matter. Its

movements are, in fact, of such a sudden and bewildering nature that the collector is often taken by

surprise and loses his quest."

Another philorheithrid, Aphilorheithrus stepheni Mosely , was observed and photographed in a similar cryptic, stick–like posture by Arturs Neboiss (pers. com.). An illustration based on this photograph was made by Charles McCubbin for the dust jacket of A Taxonomic and Zoogeographic Study of Tasmanian Caddis– flies by Neboiss (1977). This illustration is reproduced herein ( Fig. 1 ) with the kind permission of Neboiss. We believe that this type of cryptic behavioral characteristic is characteristic for most philorheithrids, especially those that have their anterior wings obliquely truncated.

Larva. The larva of Philorheithrus agilis was described by Hudson (1904) and redescribed by Cowley (1978), who mentioned that the larvae dwell in fast flowing streams, and construct cylindrical cases that are tapered slightly apically, composed of small stones, and lack posterior partitions. The larvae of Psilopsyche and Mystacopsyche have not been described, but Flint et al. (1999) mentioned that they "live in rivers and small streams, often in the sandy bottom."

Figures

FIGURE 1. Aphilorheithrus stepheni Mosely: Habitus of adult in cryptic, stick – like posture, original figure illustrated by Charles McCubbin based on photograph by Arturs Neboiss.