Carolinea 74

L amos : Tokukobelba gen. nov. (Acari: Oribatida: Damaeidae) 91 Tokukobelba mongolica is characterized by B a - yartogtokh (2000) as possessing only 7 setae on the palptarsus. On the illustration provided for this species, 8 setae are visible on the palptar- sus, but the recumbent solenidion is not depict- ed. T mongolica shows only 3 distal eupathidial setae ( B ayartogtokh 2000), similar to T compta . The seta sul appears to be absent. T rägårdh (1910, p. 521, Fig. 296) depicts the palptarsus of T . farinosa with 7 setae, not showing the sole- nidion or seta cm. Again only 3 distal eupathidial setae are seen. Two main hypotheses may account for the highly unusual palptarsal setation of Tokukobelba . The first is that the seta sul is absent and instead an additional ventral or lateral seta is present, while the second posits that seta sul exists but does not become eupathidic in ontogeny and is strongly proximally displaced on the tarsus when compared to other Damaeidae. In the legs the ontogeny of the eupathidia is al- ways progressive in that no eupathidium trans- forms back to a normal seta ( N orton 1977b) and the same appears to be the case in the palptarsus. In Tokukobelba compta the subun- guinal seta s of the tarsus of leg I, which may be a homologue of the tarsal subultimal seta is not eupathidic in the nymphs but becomes so in the adult. During ontogeny the insertion point of this seta migrates in a distal direction on the tarsus. In the larva and nymphs it is inserted proximally to setae (a) (Figs 16, 17, 18), whereas in the adult (Fig. 4) it is distal to them. It is conceivable that the subultimal setae share the same genetic pro- gram here acting on the subunguinal setae and that this, usually already active in the palptarsus prior to the larva stage, is here repressed, pre- venting the normal development and migration or distal insertion of the seta sul. If the seta here tentatively identified as vt2´ is instead a subulti- mal seta, the factors leading to the inhibition of the eupathidial nature and also the peculiar prox- imal insertion of this seta must have acted prior to the larval stage. Where it exists, seta sul is closely associated with the ultimal setae and located on the tarsal tip in all Oribatida and in primitive representatives such as Hypochthonius K och , 1835, and Colloh­ mannia S ellnick , 1928, and may even be partial- ly fused with these ( W oas 2002). If the seta sul is present in adult Brachypylina, it virtually always is eupathidic, not elongate and seta-like with a curled tip such as the ventral and lateral setae, and not with a completely different appearance to the short and stubby ultimal setae. I am not aware of any instance in Brachypylina where seta sul shows a significant proximal insertion on the palptarsus. Although it is not possible to state with absolute certainty whether the development of seta sul has been strongly retarded, effectively being suspended at the prelarval state or earlier with the normal number of ventral setae being present, or whether seta sul is just absent, I tend to favour the latter hypothesis. What is apparent is that the subultimal seta of Tokukobelba either experiences a highly unusual, early, drastic de- velopmental slow-down, or has been completely lost. Based on G randjean (1946), the setal priorities for the eupathidia of the palptarsus are as fol- lows: ul´, ul´´, acm, sul, with the latter being the one most likely to experience retardation in de- velopment or regressive loss. The loss of seta sul is most unusual in brachypyline mites, but has been noted for a few taxa such as Fosseremus quadripertitus G randjean , 1965, based on the detailed documentation of the species by its au- thor, and Veloppia ( N orton 1978b, C hen & W ang 2002). The apparent loss of the palptarsal seta sul and the presence of an extra ventral seta in Tokuko­ belba are both highly derived states. The same would apply to a developmentally retarded seta sul. Plesiomorph for the Damaeidae and also for the Brachypylina as a whole is the presence of 9 palptarsal setae, including a eupathidic dis- tally inserted seta sul. Since the 5-segmented damaeid palps are homologous to the legs, it is noteworthy that Tokukobelba is characterized not only by supernumerary ventral setae on the tar- sus of legs I and II, but also on the palptarsus, which is highly suggestive of a shared underlying developmental program. Nymphal seta c3 In all Damaeidae, the notogastral seta c3 is found in the larva and all nymphal stages but gets lost in the adult ( N orton 1977b). The on- togeny of Tokukobelba compta conforms to this pattern. Seta c3 of the larva of this species is very short and thin compared to the thick, elon- gate setae c1, c2, da, dm, dp and lp, being ap- proximately similar in length to the short lateral setae la and lm (Fig. 9). A similarly short larval seta c3, whose length approximately equals that of the rostral setae, is typical of all damaeid lar- vae.