Dimorphacanthella, Potapov, Mikhail B., Bu, Yun, Huang, Cheng-Wang, Gao, Yan & Luan, Yun-Xia, 2010

Potapov, Mikhail B., Bu, Yun, Huang, Cheng-Wang, Gao, Yan & Luan, Yun-Xia, 2010, Generic switch-over during ontogenesis in Dimorphacanthella gen. n. (Collembola, Isotomidae) with barcoding evidence, ZooKeys 73, pp. 13-23 : 13-15

Dimorphacanthella gen. n.

Description.

Ocelli and pigment absent. Abd. V and Abd. VI fused. Integument regularly and slightly reticulated, without pits. Middle-sized and large individuals with four anal spines set in one transversal row on posterior edge of Abd. V (Figs 1, 10), small juveniles with only two inner anal spines on Abd. V (Fig. 2) (unexamined small juveniles for Dimorphacanthella mediaseta ). Inner anal spines of all age stages derived from p1-setae. Setae a1 and p2 not modified to spines. Maxillary outer lobe with simple palp and 4 sublobal hairs. Prelabrum with 2 setae. In two known species labial palp lost five guards on papillae B, D, and E. Body chaetotaxy oligochaetotic. Unpaired median seta (p0) present on Abd. IV. Papilla of inner anal spine is supplied with a seta on dorsal side (absent in small juveniles). Macrosetae well differentiated, macrochaetotaxy of Th. II-Abd. III 1,1/2 –3,2–3,2– 3. Sensilla well differentiated, 2,1/1,1,1,2,4 (s) and 1,0/0,0,1 (ms) in number. Empodial appendage present, furca absent.

Distribution:

China (Shanghai, Ningxia).

Type species:

Dimorphacanthella anommatos (Chen & Yin), 1984, comb. n.

Remarks:

Sharing four anal spines on genital segment, the new genus Dimorphacanthella formally resembles three genera namely Tetracanthella , Blissia Rusek, 1985 and Sibiracanthella Potapov & Stebaeva, 1995. All four genera also have the same derivation of inner anal spines which are, following the notation of Deharveng (1978), p1-setae modified. Outer anal spines derived from p2-setae in Tetracanthella (Fig. 14) and Blissia and a1-setae in Sibiracanthella . Outer anal spines of Dimorphacanthella are modified setae positioned in posterior part of Abd. V and between two macrosetae pp1 and pp2. Since the designation of setae of Abd. V is not developed enough we notate these setae as setae x on the schemes (Fig. 15). Seta x is a ordinary seta in late instars of Tetracanthella , while in Dimorphacanthella it is modified to a spine at later instars and absent at early instars (Figs 14-16). Seta p2 which is a lateral spine in Tetracanthella remains unmodified in Dimorphacanthella and is located anterior to and between sensilla s1 and s2. The new genus has a pair of ordinary setae in front of median spines in late instars (notated as m1 seta by us) (Figs 15). These setae were never seen in other genera having spines in p1-position. These and other differentiated characters of genera with four anal spines are presented in Table 1.

Blindness and presence of unpaired seta on Abd. IV are only shared with Martynovella nana nana (Martynova, 1967) described from Central Asia. This species, however, has two anal spines at all age instars, more complete sensillary set, lacking seta m1 in front of spines, and other less significant differentiating features. Another subspecies, Martynovella nana kirgisica (Martynova, 1967) has no unpaired seta on Abd. IV.

The number and homology of real anal spines are of high value in generic taxonomy of Anurophorinae and appeared to be constant in the course of postembryonic ontogenesis ( Deharveng 1978), except epitokous and ecomorphic forms of Proisotoma Börner, 1901 and Cliforga Wray, 1952 ( Fjellberg 1988; Najt 1983). In the family, Dimorphacanthella anommatos is the only case where the real anal spines on high papillae appear after moulting.

Etymology:

The name of the new genus refers two morphs, juvenile and adult, having different number of anal spines in at least one species of the genus.