Aggressopygus sibiricus, Potapov & Babenko, 2014

Potapov, Mikhail & Babenko, Anatoly, 2014, About some unusual Asiatic taxa of Isotomidae (Collembola), Journal of Natural History (J. Nat. Hist.) 48 (29 - 30), pp. 1835-1851 : 1847-1849

Remarks on Micrisotoma achromata Bellinger, 1952

Figures 4C , 7B

Material

Canada, south-western part of Nova Scotia, Kejimkujik National Park , N 44.23° W 65.13°, 22.IX.2006. leg. S. Jayanetti (22 specimens) . Japan, Kamigamo experimental forest of Kyoto University , nearby Kyoto, leg. S. Fujii (two specimens) ; Russia, Far East, South Kuril Islands, Kunashir Island , Yuzhno-Kuril’ sk, spruce forest, 18. VI.1990, leg. S. Bugrov (two specimens) ; Indonesia, Sulawesi, Selatan, Gowa, Malino , 2460 m. alt., 20.VIII.1990, leg. L. Deharveng and A. Bedos (six specimens) .

The species was described from the eastern part of USA (Connecticut) and was given generic rank due to the unusual PAO divided into five lobes, unusual blunttipped setae on abdominal tip and serrated macrosetae. It has been recorded from other locations of the USA, Canada, Japan, Far East of Russia, and NE China ( Christiansen and Bellinger 1998; Furuno et al. 2000; Potapov 2002; Gao et al. 2009). New material of M. achromata studied by us indicates that its distribution is even wider, at least from Canada to Indonesia. This morphologically remarkable species is probably parthenogenetic (only females have been seen) which may partly explain its wide geographic distribution.

Several publications give the information on taxonomy of M. achromata ( Yosii 1965, 1976; Potapov 2001, 2002), and the genus Micrisotoma was recently included in the ‘ Cryptopygus complex’ by Potapov et al. (2013).

Apart from a complex PAO and special foil setae the genus is also unique because of modified chaetotaxy of abdomen. Median areas of the five first abdominal tergites are unusually oligochaetic: Abd. V and Abd.IV has only 2 + 2 axial setae, Abd.III usually 2 + 2 (more rarely 3 + 3), Abd.I and II has 2 + 2 or 3 + 3. The reduction of Abd. V both in number of setae and dorsal length is also uncommon, and is shared with only a few unrelated genera ( Archisotoma Linnaniemi , Isotomodes Linnaniemi , and Secotomodes Potapov ). In addition, Abd. VI has special ‘tiny’ setae alternating with foil setae ( Figure 7B ): 7 in anterior and 2 + 2 in posterior rows. After the redescription of Fjellberg (2007) similar setae, but in fewer numbers, were found in European species of Hemisotoma : H. scapelliferus (Gisin) and H. albaredai (Selga) but the nature of this similarity is not fully understood.

We have not found any significant differences between the specimens from distant localities listed above, and give a generalized redescription which completes characteristics known so far for this species.

Additional description

Maxillary outer lobe with 4 sublobal hairs, maxillary palp bifurcate. Labium with 5 papillae (А–Е), 15 guard setae (e7 absent), 3 proximal and 4 basomedian setae. Ventral side of head with 3 + 3 setae, of which posterior 2 + 2 inserted close together. Sensillary chaetotaxy of antennae generally as in Aggressopygus gen.nov., Ant.3 with 1 large bms and 1 lateral s. Organite on Ant.4 stick-like. Axial chaetotaxy as 10,6/2–3,2–3,2–3,2. Sensillary formula as 4,3/2,2,2,3,5 (s), microsensilla (ms) as 1,0/0,0,0 ( Figure 4C ). Tergal sensilla well differentiated, on most tergites shorter and thinner than common setae. Medial sensilla on Th. II –Abd.IV in p-row. Abd. V with 5 sensilla arranged as 3 dorsal short (al, accp1, accp2), one lateral middle-sized sensillum (accp3) thicker than dorsal, and one ventral middle-sized ( Figures 4C , 7B ). Macrochaetae ciliated, 1,1/3,3,3,4 in number, medial ones on Abd. V 2.6–3.7 times longer than inner edge of unguis. Foil setae tubular, with thin cilia on distal half. 13 foil setae arranged in two transversal rows as 4 + 4 anterior (fa1, fa3, fa5, fa7) and 5 posterior (fp0, fp2, fp4). Thorax without ventral setae. Ventral tube with 4–6 + 4–6 laterodistal and with 4 posterior setae arranged in two transversal rows. Tenaculum with 4 + 4 teeth and one (more rarely two) seta. Anterior furcal subcoxae with 9–11, posterior one with 8(7–9) setae. Anterior side of manubrium with 2 + 2 (more rarely with 3 on one side) setae. Dens with 18–20 anterior setae. Posterior side of dens crenulated and with 5 normal setae (3 basal and 2 at the middle) and one rudimentary minute seta subapically (not seen in some specimens).

Figures

Figure 4. Habitus and chaetotaxy of Aggressopygus sibiricus sp. nov. (A), Aggressopygus armatus sp. nov. (B), and Microisotoma achromata (C).

Figure 7. Posterior part of abdomen of Aggressopygus sibiricus sp. nov. (A) and Micrisotoma achromata (B). s – sensillum, ms – microsensillum, fa – foil seta, tc – ‘tiny’ seta.