Isotopenola, Potapov, Mikhail, Babenko, Anatoly, Fjellberg, Arne & Greenslade, Penelope, 2009

Potapov, Mikhail, Babenko, Anatoly, Fjellberg, Arne & Greenslade, Penelope, 2009, Taxonomy of the Proisotoma complex. II. A revision of the genus Subisotoma and a description of Isotopenola gen. nov. (Collembola: Isotomidae), Zootaxa 2314, pp. 1-40 : 27-28

Isotopenola gen. nov.

Type species: Cryptopygus australis Womersley, 1934

Diagnosis. With all abdominal segments clearly separated, Abd.VI partly hidden under Abd.V, not visible in dorsal view. ( Figs 14 , 85 ). 8+8 ocelli, bms on Ant.3 absent. Maxillary palp simple, 4 sublobal chaetae, number of guard chaetae on labial papilla E reduced (two or three е-guard chaetae absent), two prelabral chaetae present. B-row of chaetae on Ti.1−2 complete (unpaired B4/5 absent). Folsomides -like furca: manubrium without anterior chaetae, dens smooth with 1 (apart from I. nilgiris ) anterior and few posterior chaetae. Tergal sensilla on abdomen situated in front of p-row of chaetae, number of microsensilla on tergites varies (from 11/ 111 to 10/101), ventral chaetae on thorax absent, macrochaetae hardly differentiated, VT with 4+4 laterodistal and more than 2 posterior chaetae, tibiotarsal tenent chaetae (1−2−2) clavate. Ventral and part of lateral sides of a body with visible secondary granulation. Known species have 4+4 teeth on tenaculum.

Representatives. Apart from the type species ( Isotopenola australis ( Womersley, 1934) comb. nov.), other described species belong to the new genus, Isotopenola loftyensis Womersley, 1934 comb. nov., Isotopenola nilgiris ( Denis, 1947) comb.nov. and Isotopenola delicata sp. nov., and four possibly undescribed species from Australia, New Zealand and New Hebrides.

Affinity. Because of the ventral position (i.e. cryptopygy) of the last abdominal segment, C. australis and many other southern species were placed by Australian and New Zealand taxonomists in the genus Cryptopygus Willem, 1901 . It is now recognised that Cryptopygus consists of many dissimilar taxa and groups of species (see: Potapov 2001; Rusek 2002; Deharveng et al. 2005). Consequently a reliable diagnosis for the latter genus is not possible at present. Nevertheless, the new genus Isotopenola can be easily distinguished at least from the type species of Cryptopygus by of the non fusion of the two last abdominal segments (versus fused) and other features including outer mouth parts.

The new genus resembles most closely Eurasian Subisotoma although the similarity could have either a phylogenetic or convergent origin. Both genera share the same structure of outer mouth parts (simple maxillary palp, 4 sublobal chaetae, 2 prelabral chaetae), unsetaceous anterior side of manubrium and similar chaetotaxy of dens and ventral tube. Isotopenola gen.n. differs by having distinct secondary granulation on sterna (versus more or less smooth in Subisotoma ) and the presence of submedial setaceous fields ventrally on Abd.III (marked as sf–III in Figs 86 , 106 , 116 ). Submedial setaceous fields are groups of chaetae which are positioned between tenaculum and main setaceous areas of a tergite. In species of Subisotoma ' asiatica ' group the associated area can be formally occupied by a single chaeta separated from the main setaceous area ( Figs 60 , 62 ). These fields have not been seen in other members of Anurophorinae so far. As well the species examined in the new genus have 4+4 teeth on tenaculum (versus 3+ 3 in Eurasian Subisotoma ), the posterior side of dens usually has more than 5 chaetae (versus 3–4), and additional sensilla (as) and basal microsensilla (bms) on Ant.3 are absent. In the last character Subisotoma is not homogeneous; in species of the ' pusilla ' group as and bms are always present, but in ' asiatica ' group as is absent and bms may be present or absent. Tergal sensilla in Isotopenola gen. nov. are more numerous and situated in more anterior position than in Subisotoma . Pronounced cryptopygy and plump body shape could also define Isotopenola gen. nov. but these characters are difficult to observe as they depend on the position and compression of a specimen on the slide. Species of the genus Subisotoma also are moderately cryptopygic as Abd.VI is often hidden under Abd.V. The material from Australia, New Zealand and adjacent regions that we were able to study is limited but the literature indicates that a number of species described from these regions may belong to Isotopenola : Cryptopygus atratus Salmon, 1941 , C. granulatus Salmon, 1943 , C. haweaensis Salmon, 1941 , C. minimus Salmon, 1941 , C. niger Carpenter, 1925 , C. okukensis Salmon, 1941 , C. terrigenus Salmon, 1943 are all possible candidates because they have an independent and ventrally positioned last abdominal segment and Folsomides -like furca.

Distribution. Likely to be widely distributed throughout eastern Australia and New Zealand, and in tropical Asia.

Name derivation. During our study of Australian material we consulted an unpublished revision of Cryptopygus by P. Lawrence in which the type material of Cryptopygus australis and C. loftyensis were studied. So, we dedicate this genus to Peter Nolan Lawrence, an exceptional and original British taxonomist.

Figures

FIGURES 13 – 14. General habitus (laterally): 13, Subisotoma bisensillata, 14, Isotopenola sp. 4 (New Zealand, Mt. Stokes Track).

FIGURES 83 – 88. Isotopenola australis. (Australia, Northern Territory, Emily Gap): 83, postlabial chaetae (encircled); 84, ventral side of Th. III; 85, profile of three last abdominal segments; 86, ventral chaetotaxy of Abd. II – V (tenaculum not shown); 87, Th. II; 88, Abd. V, sf – II and sf – III – setaceous fields on Abd. II and III, respectively.

FIGURES 106 – 115. Isotopenola delicata sp. nov.: 106, ventral chaetotaxy of Abd. II – IV; 107, profile of three last abdominal segments; 108, postlabial chaetae (encircled); 109 – 111, chaetotaxy of tibiotarsi of legs 3 (109), 2 (110), and 1 (111); 112, Th. II; 113, Abd. V; 114, mucro and dens; 115, ocelli, PAO, and Ant. 1, sf – II and sf – III – setaceous fields on Abd. II and III, respectively.

FIGURES 116 – 117. Isotopenola spp.: 116, Isotopenola sp. 4 (New Zealand), ventral chaetotaxy of Abd. II – IV (tenaculum not shown); 117, I. nilgiris, dens and mucro, and apical part of dens, dorsal view. sf – II and sf – III – setaceous fields on Abd. II and III, respectively.

FIGURES 58 – 60. Subisotoma asiatica (paratype): 58, chaetotaxy of Abd. III; 59, area of posterior part of head (high magnification); 60, ventral side of Abd. III (pair of isolated chaetae encircled), sock. –– chaetal socket.

FIGURES 61 – 63. Subisotoma cruda sp. n.: 61, Ant. 3, dorsal view; 62, ventral chaetotaxy of posterior part of abdomen and furca; 63, chaetotaxy of Abd. V.