Rakantrechus
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publication ID |
https://doi.org/ 10.50826/bnmnszool.48.3_119 |
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persistent identifier |
https://treatment.plazi.org/id/A95B8783-3905-FFED-FEA6-FC8DFC56C67F |
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treatment provided by |
Felipe |
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scientific name |
Rakantrechus |
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Rakantrechus View in CoL Complex
Range of taxa. Comprising ten genera: Ishikawatrechus Habu, 1950 , Ryugadous Habu, 1950 , Rakantrechus S. Uéno, 1951 (including Iyotrechus S. Uéno et Naitô, 2009 ; see below), Kusumia S. Uéno, 1952 , Awatrechus S. Uéno, 1955 , Yamautidius S. Uéno, 1957 , Himiseus S. Uéno, 1969 , Allotrechiama S. Uéno, 1970 , Nipponaphaenops S. Uéno, 1971 , Chaetotrechiama S. Uéno, 1982 . It seems worthy of attention that sometimes the term, l Rakantrechus Complexz , is ambiguously used to indicate a part of the taxa listed above. For example, in Uéno (2010, p. 131), and Uéno and Naitô (2009, p. 245), the term l Rakantrechus Complexz refers, at least explicitly, only to the subgenera of the genus Rakantrechus . However, in any case of the temporal variant usage, the term is used to indicate a part of the Rakantrechus Complex defined above, usually centering the genus Rakantrechus .
General morphology. First pore of the marginal umbilicate series of elytra is usually slightly to weakly removed dorsad from latero-marginal border; more obviously removed (regarded as a re-appearance of plesiomorphy; Jeannel, 1928) in the nominate subgenus of Rakantrechus , in Yamautidius , and in subgenus Tanakaphaenops subgen. nov. of Nipponaphaenops than in the others ( Figs. 3d, g–h View Fig ). Elytra usually with two longitudinal series of discal setae, but with only external series (derivative) in some species of Kusumia , Awatrechus , and in all species of Himiseus ( Fig. 4 View Fig ). The number of discal setae is comparatively large in Chaetotrechiama , in some species of Rakantrechus subgenus Paratrechiama , which is supposed to be related to the former, and in some species of Kusumia ; and the chaetotaxies represented by them are likely to be comparable with the plesiomorphic types of the Rakantrechus Complex, even though the first case is possibly an example of atavism (cf. Figs. 4 View Fig and 7 View Fig ) ( Uéno, 1982a, p. 52). Genae usually pubescent, glabrous (derivative) only in some species of Rakantrechus and Ishikawatrechus , and in all species of Nipponaphaenops . Posterior latero-marginal setae of pronotum usually present, absent (derivative) only in some species of Rakantrechus , Ishikawatrechus , and Nipponaphaenops . Inclined face of elytral basal peduncle deeply furrowed in all species of four genera, Kusumia , Ryugadous , Awatrechus , Ishikawatrechus ( Fig. 3a View Fig ); of these in the former two genera, body surface is almost entirely densely pubescent (plesiomorphic) both on dorsum and venter ( Fig. 2n View Fig ); also in Awatrechus species body surface is usually nearly entirely pubescent except on dorsum of head and protibia, but rarely glabrous also on elytra; in Ishikawatrechus species surface varies from nearly entirely pubescent (except on dorsum of head and protibia) to entirely glabrous. Within the genera without basal transverse furrow of elytra, body surface is nearly entirely pubescent only in Himiseus and subgenus Miyamaidius S. Uéno of Yamautidius . Last visible ventrite usually with a pair of apical setae in male, with two pairs of them in female ( Figs. 2g –m View Fig ); but in Kusumia , in Himiseus , and in the nominate subgenus of Ryugadous with two pairs (plesiomorphic) in male; and in Kusumia , in Himiseus , and in the subgenus Nothaphaenops S. Uéno of Allotrechiama with three pairs (plesiomorphic) in female ( Fig. 2n View Fig ).
Identification. Usually discriminated from the other genera of the Trechiama Phyletic Series by the non-aggregate condition of the humeral set of marginal umbilicate pores of elytra. However, the following exceptional cases rarely occur in Trechiama species: pore 1 of the umbilicate series is dorsally translocated ( Fig. 3b View Fig ); pore 4 of the series is relatively widely removed from the pore 3 (or pore 1 from pore 2) (cf. Uéno, 1972, 1983). Nevertheless, even in these cases, usually distance between the pores 1 and 4 (as a value U4–U1) is smaller, and the pores 4 and 5 are closer to marginal border in Trechiama species than in the constituents of the Rakantrechus Complex. Besides, widely pubescent areas of body surface, which are present in the great majority of the species belonging to the Rakantrechus Complex, are not found in Trechiama species neither on dorsum nor on venter, even though small number of hairs are very rarely present on some parts of body surface (genae, pronotum, anterior face of protibia) also in Trechiama species ( Fig. 3b View Fig ) (e.g., Uéno, 1959, 1972).
Geographic range. Southwestern Japan, mostly south of the Median Tectonic Line; more precisely, with two exceptions, distributed in southern part of the Kii Peninsula, southern part of Shikoku, and central part of Kyushu, but the subgenus Uozumitrechus S. Uéno, 1958 of Rakantrechus occurs in westernmost part of Honshu and the islands of the Seto Inland Sea, and the subgenus Miyamaidius S. Uéno, 1978 of Yamautidius occurs in north-western corner of Shikoku.
Remarks on distribution. Constituents of the Rakantrechus Complex are mostly distributed on the southwestern side of the range of the genus Trechiama in the Japanese Archipelago, with some sympatric (with Trechiama species) areas in the westernmost Honshu and in eastern Shikoku ( Fig. 7 View Fig ). Taiwanese Trechiama species are distributed to the southwest of the Rakantrechus Complex ( Uéno, 1988).
Explanation of Figure 4 View Fig . Diagrams in Figure 4 View Fig illustrate supposed derivation mode of elytral discal chaetotaxy in each genus of the Rakantrechus Complex; the left side of arrow is ancestral state and the right side is derivative one. These follow from two criteria: having plural series of discal setae is plesiomorphic; having larger number of discal setae is plesiomorphic ( Uéno, 1988), plus two conditions: increase in the number of setae is not permitted; the transposition of setae between internal and external series is not taken into consideration. Even though Uéno (1988) simply asserted these criteria, they may not be universally valid for entire Trechini ; however, as far as the members of the Rakantrechus Complex are concerned, use of these criteria seems to be safely justified. Except asterisked one, all the chaetotaxy illustrated in diagrams occur in the extant species of the Rakantrechus Complex, i.e., variety is restricted to a minimum; therefore, it is possible that the number of discal setae is larger (or smaller) in unknown ancestral (or derivative) states than illustrated ones. Sole asterisked chaetotaxy in Ishikawatrechus is only hypothetical one; under the above supposition, it is required that the common ancestor of Ishikawatrechus should have had at least two discal setae in both internal and external series. Ishikawatrechus species having this chaetotaxy is either as-yetunfound or non-existent. Note that, within the previously known species having deep basal transverse furrow on elytra, plural discal setae are not present in both internal and external series. Finally, it cannot fail to be noticed that the augmentation and the transposition (between striae 3 and 5) of discal setae are, unlike otherwise premised sequences above, not unrealistic as casestudied in some Trechini groups (e.g., Jeannel, 1954, p. 159, 176).
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