Pauropygus pacificus, Potapov, Mikhail, Gao, Yan & Deharveng, Louis, 2013

Potapov, Mikhail, Gao, Yan & Deharveng, Louis, 2013, Taxonomy of the Cryptopygus complex. I. Pauropygus - a new worldwide littoral genus (Collembola, Isotomidae), ZooKeys 304, pp. 1-16 : 10-13

Pauropygus pacificus sp. n. Figs 21-24

Material.

Holotype: China, Shandong Province, Yantey City, sea coast near Tuchengzi Hills, sandy beach, collected by flotation of thin sand under sparse vegetation on dunes, 22.04.2011, leg. Huang C.-W., Luan Y., and Potapov M.B.; 3 paratypes: at the same place; 2 paratypes: China, Hainan, western coast, nearby Changhua town and ca 5 km NE from the town, in both locations by flotation of sand with plant roots in dunes of sea coast, leg. Bu Y., Huang C.-W., Kuznetsova N.A., Potapov M.B. 06.04.2011. Material is deposited in Institute of Plant Physiology & Ecology, Shanghai (holotype and two paratypes) andin Moscow State Pedagogical University (three paratypes).

Description.

Size about 0.4 mm. White, without eyes. Cuticle smooth. PAO about 1.7 as long as inner edge of U.III and somewhat shorter (0.8-0.9) than width of Ant.I. Outer (Fig. 23) and inner mouthparts principally as in Pauropygus caussaneli . Ventral side of head with 5+5 postlabial chaetae. Ant.I with about 18 chaetae, 1 ventro-basal (bms) microchaeta (dorsal bms not differentiated), and 2 thick ventral sensilla (s), short and long. Ant.II with 3 bms and 1 thick laterodistal s. Ant.III without bms and with 5 distal s of which two inner thicker and longer than outer ones. Male antennal “spurs” present.

Thorax without ventral chaetae. Dorsal macrochaetae smooth, weakly differentiated, as 3,3,3,4 on Abd.I-IV. Medial macrochaetae on Abd.V about 0.4 as long as dens. All sensilla of thorax and medial sensilla of abdomen nearly as long as ordinary chaetae and hardly visible, lateral sensilla on Abd.III-V shorter than ordinary chaetae. Microsensilla absent. Sensillar formula 31/11221 (s), 00/000 (ms) (Fig. 21). Sensilla in posterior position. Microsensilla on Abd.I absent (Fig. 22).

Unguis of normal shape, without inner tooth, two broad unequal lateral teeth. Upper subcoxa of Leg I-III with 1,1,4 chaetae, lower subcoxa with 1,6-7,7-8. Ti. I–III with 20, 21,>25 chaetae. Distal tibiotarsal tenent chaetae on Ti. I–III (1-2-2) well developed, not clavate, about 1.1-1.2 as long as U.III. Each tibiotarsus with one additional tenent chaeta at middle part. Ti.III with one stick-like chaetae (A7) in distal ring. Tenent hairs (1,2,2) slightly longer than U.III. Pretarsus with two chaetae. Ventral tube with 4+4 laterodistal and 4 posterior chaetae in one transversal row. Tenaculum with 4+4 teeth and 1 chaeta. Anterior furcal subcoxa with 12-14 chaetae, posterior with 6 ones (rarely 5). Manubrium principally as in previous species. Dens slender, anteriorly with 10-12 chaetae. Posterior side of dens slightly crenulated in the medial part, with 5 chaetae of which 3 basal and 2 at the medial part (short inner and long outer) set together on low papillum. Mucro slender with two teeth of unequal size (Fig. 24). Ratio of manubrium: dens: mucro = 3.7-3.8: 4.0-5.0: 1. Anal lobes without microchaetae.

Affinity.

The complete absence of microsensilla on body of Pauropygus pacificus sp. n. is the second reported case among Isotomidae (so far only known in Proisotoma minima ). This peculiarity remains the only difference between Pauropygus pacificus sp. n. and Pauropygus caussaneli . Taking into consideration also the different distribution ranges of these species we prefer to consider them as two independent species.

Name derivation.

The species is probably distributed in the sands all over the Pacific coast of China.

Distribution.

Known from two distant localities on Pacific coast of China.

Taxonomical remarks on genera similar to Pauropygus

Examination of numerous species of the Cryptopygus complex revealed that six genera of this complex share the posterior position of sensilla on the three first abdominal segments. Like in other taxa of Isotomidae , as for instance in Proisotoma complex (Potapov et al., 2006) and in species groups of Folsomia (Grow & Christiansen, 1976; Deharveng, 1979), the position of medial sensilla on abdominal tergites (within or well in front of posterior row of chaetae) is taxonomically very relevant at supraspecific level. The posterior position of sensilla is shared by several genera of the Cryptopygus complex and not necessarily indicates close relationships, but rather might be a result of convergent evolution. It is for instance the case in the genus Micrisotoma Bellinger, 1952 which also belongs to Cryptopygus complex and shows relationships with Hemisotoma Bagnall, 1949 in which sensilla are in mid-tergal position (type species Isotomina thermophila ).

To figure out the relation between these genera, we propose below a key to the genera of the Cryptopygus complex with posterior position of sensilla on three first abdominal segments. Pauropygus projectus sp. n. lost posterior sensilla and can be identified by pleural fold; the loss of mentioned sensilla is probably shared with several species of Arlea but descriptions do not give information on these characters. The position of the odd genus Appendisotoma is not fully decided: six species studied by us ( Appendisotoma abiskoensis (Agrell), Appendisotoma bisetosa Martynova (types), Appendisotoma sibirica Stebaeva (types), and three species from Far East Russia and North America) have 11 apical chaetae on tibiotarsi while other four ( Appendisotoma stebayevae (Grinbergs), Appendisotoma montana (Martynova), Appendisotoma juliannae (Traser et al.), and one species from Kazakhstan) show common set for the subfamily (7 chaetae). We include the genus Appendisotoma in the key since it formally matches the diagnosis of Cryptopygus complex.

Key to genera of Cryptopygus complex with sensilla in posterior position on body tergites

The key is based on examination of three species of Pauropygus , four of Proisotomodes (one undescribed), two of Isotominella (one undescribed), eight of Appendisotoma (two undescribed), and one of Micrisotoma .