Idiommata Ausserer

file:///D:/MyDocuments/htmls%20for%20public/Idiommata.html SILVER BACKS & GIANT BRUSHFOOTED TRAPDOOR IDIOMMATA AUSSERER Family Barychelidae Dr Robert J. Raven Queensland Museum, PO Box 3300, South Brisbane, Q. 4101. Idiommata are large heavily dark funnel-web like spiders that build either burrows with open doors and lower isolated flask-like chambers or the chamber may be just below the ground and all you see is a door. W e call the males Silverbacks because they have a pile of dense silvery hairs on the head; the females either have golden brown or dark brown hairs. They all belong to the family Barychelidae are Brush- footed spiders and this term refers to the dense pad of hairs on the ends of the legs; these spiders also have short stumpy spinnerets that are not usually seen unless the spider is upside down. Tarantulas or whistling spiders, on the other hand, have quite distinctive finger-like spinnerets out the end of the abdomen or body. There are over 150 species of Barychelidae in Australia which makes us the most highly diversity country in the world. Barychelids range from quite large spiders, like the Silverbacks, down to the truly tiny bark-dwelling Sason in the W et Tropics. Idiommata is the lar gest of the Australian barychelids and make be the largest in the world and vie in size with some of the Australian tarantulas. They occur predominantly away from south-east Queensland and the south-east coast, as they seem to prefer warmer winters. The group is unusual in the family in that, like the Australian tarantulas, they possess a sound-making structure (maxillary lyra) on the mouthparts. The structure is among the smallest in relatively size so it is not clear whether the sound is audible to us. The sounds made by Australian tarantulas are audible in a quiet area as a hiss. 1 of 4 27/04/2010 5:02 PM file:///D:/MyDocuments/htmls%20for%20public/Idiommata.html BURROW S Barychelid burrows vary from temporary silk cells to complex burrows with concealed doors; most are not very deep (i.e., more than 40cm). Contrary to Main (1976, p. 75), many barychelids do not build doors on their burrows. In a number of Synothele, Mandjelia, Ozicrypta, Encyocrypta, Sason, and probably Monodontium, the `burrow' is simply a short barrel-shaped nest of silk with a soft door at each end. Those burrows may be found in leaf litter attached to the underside of logs, rocks, or leaves (most genera), attached to a tree (Encyocrypta cagou), within rotting logs, or built into a shallow depression in the tree with abutting doors flush with the bark surface (Sason). The first modification of that would seem to be the subterranean Y-shaped burrow with two external doors (Mandjelia banksi, Seqocrypta jakara). In some Encyocrypta, the burrow may lack doors (e.g. E. aureco) or may have a thick door (E. bouleti, E. mckeei, E kottae); and E. oubatche which builds in the soft bark of Melaleuca paperbark trees. Other genera with species that build simple sinuous subterranean tubes with thick or thin doors are Barycheloides, Barychelus, Orstom, Mandjelia, Ozicrypta, Zophorame, Tungari, Rhianodes, and Nihoa (Churchill & Raven, 1992). Idioctis species all make simple burrows with one door but in different intertidal and near littoral substrates from mud, though mangrove trees and logs, to coral rock, and ironstone boulders (Churchill & Raven, 1992). Finally, some species (Trittame, some Idiommata, presumably Barychelus badius) build burrows without exterior doors, and the entrances are thickly `clothed' with leaves. A short side-shaft arises at the horizontal from the main shaft from which it is separated by a thick plug door. Idiommata also builds a shallow flask-shaped burrow with the thick door opening directly on the surface. The burrows are found in a wide diversity of microhabitats. Many are found on embankments but none here have been recorded in banks of creeks, rivers or streams either in Australia or New Caledonia (contrary to Main, 1976, p. 88); some have been found on trees near watercourses. That contrasts with idiopids (pers. obs.), nemesiids (Raven, 1984a), diplurids (Raven, 1984b), and hexathelids (Raven, 1978) that are are often found on the banks of watercourses in rainforest or closed forest. By far, barychelids are most commonly found on a flat or sloping forest floor. No genus seems to be found exclusively in one habitat. Because the number of barychelid burrows in embankments remote from waterways often outnumbers those on gently sloping ground and those, if any, near waterways, Main's oft repeated suggestion (e.g. Main, 1976, p. 77; Main, 1993) that doors are an anti-flooding adaptation, seems to lack support, except possibly in W estern Australia. HABITAT. Barychelids are found from the littoral and supralittoral zones, through open sclerophyll forests, vine thickets and rainforest. The dominance of rainforest endemics (35% from that habitat) in species herein is considered only a result of unbalanced attention directed at that habitat in northern Australia. Recent collections from the dry forests around Rockhampton and Townsville yielded far more barychelids than expected. Much more attention needs to be directed at vine thicket habitats in northern Australia before a reasonable comparison of habitat richness can be made. Only few barychelid genera are known to be habitat endemic: Orstom, Natgeogia, Questocrypta and Barycheloides in New Caledonia; Rhianodes in Singapore and Malaysia; and presumably Monodontium in New Guinea and Singapore. Idiommata is commonly considered a xerophilic group but the Queensland Museum holds material from vine thickets and dense tropical rainforest, as well as open eucalypt forest. Idiommata males in Queensland have been taken in almost all months but most are taken from December to June. ENVENOMATION Only four barychelid species are known to have bitten humans in Australia. Idiommata blackwalli varies from `extremely poisonous' (Main, 1967) to `poisonous' and `Non-lethal, local reactions only...' (Main, 1976, p. 279). Sutherland (1983, p. 235), however, reports only local pain and swelling. Specimens of two species of Mandjelia, M. brassi and M. paluma, and Ozicrypta littleorum, bit their collectors with only minor local pain for 10-20 minutes. No studies are known on barychelid toxins. No dangerous envenomations from Idiommataare reported from eastern Australia. 2 of 4 27/04/2010 5:02 PM file:///D:/MyDocuments/htmls%20for%20public/Idiommata.html PREDATORS & PARASITES I have noted the large (total length about 20-30cm) scolopendrid centipede Ethmostigmus in burrows of Idiommata blackwalli. In the case of Idiommata, the female had lept up about 2-3cms out of its burrow, presumably in fleeing from the centipede. That also suggests that the centipede did not enter the burrow down the open tube but also broke through. Given the vulnerable nature of the two-doored burrow, predation by litter feeding birds would seem possible. FOR THE MORE SCIENTIFICALLY MINDED MAXILLARY LYRA. This is a transverse band of long thick spines on the anterior face of the maxillae directed down the face. It interacts with a line of fine `pins' or `strikers' along the outer edge of the cheliceral furrow. The pins are believed to act across the lyra spines and cause sound. In Selenocosmia, sound is made when the spider is aggravated and is an audible hiss (pers. obs.). (Goloboff (in litt.) reports the same sound in the theraphosids Acanthoscurria sternalis and Pseudotheraphosa.) No sound has been recorded from the lyra of a barychelid. In all taxa known, the lyra occurs in both sexes. It is found in many theraphosids and diplurids, Diplura and Trechona (Raven, 1985b), as well as the barychelid Idiommata and here in a weak form newly reported in Aurecocrypta lugubris. Main (1967) indicated that Lampropodus (since synonymised with Idiommata) differs from Idiommata in lacking a stridulatory lyra. However, the types of all species originally placed in Lampropodus all have a distinct lyra. Form of the lyra in Idiommata is similar to that in theraphosids. However, the fine structure of the setae are different. The comparison will be explored elsewhere. W ithin barychelids, the lyra of Idiommata is different in strength, position, and insertion to that of Aurecocrypta lugubris. In Idiommata, the spines are a narrow band of setae directly on the face of the maxilla. The spines are rigid and much thicker than the surrounding setae. The shaft is long, cylindrical, and smooth. They have an incrassate subapical portion tapering to a unilateral finely fimbriate tip. Also, the spine bases are about central on the maxilla. Number and size of spines varies in some species. In Aurecocrypta, setae are in a single line in a shallow groove, similar in position to the groove of Rhianodes. The setae are noticeably thicker than setae above them but about as thick as the long red hairs along the lower front edge of the maxillae. Shafts are long basally smooth but deeply fluted, whorled and fimbriate for their length; the lyra setae are not rigid. No specialised setae are evident on the cheliceral edges. Hence, the structures in Idiommata and Aurecocrypta are not considered homologous. REMARKS. The most diagnostic characters of Idiommata are the very conservative spiralled form of the palpal bulb and the large size of the tibial spur. Exerpt from: Raven, R.J. 1994 07 25: Mygalomorph spiders of the Barychelidae in Australia and the western Pacific. Memoirs of the Queensland Museum 35 (2): 291-706. Scientific Details Idiommata Ausserer Idiommata Ausserer, 1871, p. 183. Type-species by monotypy, Idiops blackwalli O. P.-Cambridge, 1870. Thorell, 1881, p. 243; Simon, 1892, p. 117; Rainbow, 1911, p. 114; Roewer, 1942, p. 214; Bonnet, 1957, p. 2286; Brignoli, 1983, p. 129; Main, 1985, p. 13; Raven, 1985b, p.

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