It was found that all Acheilognathinae had a series of four to seven infraorbital bones of which the third (except Acheilognathus typus) was extraordinary large. Within the bitterlings, the five bone series state was the most common. This five bone series state is more conservative among all subfamilies of the Cyprinidae than a smaller or greater number: e.g., in Acheilognathinae, Bogutskaya & Komlev (2001); in Leuciscinae, Barbour & Miller (1978), Bogutskaya (1991b, 1992, 2000), Chen (1987, 1996), Howes (1984b), Hoyt (1972), Mayden (1989); in Xenocyprinae, Bogutskaya (1991b), Cao & Meng (1992), Howes (1981); in Cultrinae, Yang & Chu (1987), Howes (1979); in Squaliobarbinae, Bogutskaya (1991b), Chen (1987), Howes (1981); in Tincinae, Chen (1987); in Barbinae, Chen (1989), Howes (1987), Zhou (1989); in Labeoninae, Chen (1989); in Cyprininae, Chen & Yang (2002), Watanabe (1996), Zhou (1989); in Gobioninae, Hosoya (1988), Yu & Yue (1996); in Rasborinae, Ashiwa & Hosoya (1998), Howes (1984a), Howes & Teugels (1989), and Lee & Kim (1987). Fewer than 5 infraorbital bones have been reported in subfamilies other than Acheilognathinae: Leuciscinae from North America (Chen, 1996; Mayden, 1989; Woodman, 1992), Barbinae (Chen, 1989; Farm, 2000), Cyprininae (Vasil'yeva, 1990), and Rasborinae (Lee & Kim, 1987; Weitzman & Chan, 1966). More than 5 infraorbitals have been reported in subfamilies other than Acheilognathinae: Eurasian Leuciscinae (Howes, 1978; Zupančič & Bogutskaya, 2000) and North American Leuciscinae (Barbour & Miller, 1978; Mayden, 1989), Gobioninae (Hosoya, 1988), Xenocyprinae (Howes, 1981), Barbinae (Wu & Wu, 1992), and Cyprininae (Vasil'yeva, 1990; Watanabe, 1996).
Mapping of infraorbital states onto a molecular tree (Okazaki et al., 2001) confirmed that the five infraorbital series state is plesiomorphic (Fig. 13). This suggests that there are two polarities: from 5 to 4, and from 5 to 6 or 7. The six- or seven-infraorbital series state is a synapomorphy of A. longipinnis, A. macropterus, A. t. tabira, A. tabira subsp. (a), and A. typus (Table 1). Also, a reduced posterior portion of 'io 2' was considered to be a synapomorphy of A. longipinnis and A. typus (Figs. 10 H and I). Although a small bone was found in A. typus between the 'io 2' and 'io 3', its homology is indetermibable, but might be an autapomorphy of A. typus (Fig. 10I). Increase of the infraorbital bones may reflect evolution of Acheilognathus from Tanakia or its ancestor, while decrease of the infraorbital bones may reflect evolution of Rhodeus from Tanakia or its ancestor.
Nakamura (1969: 335) in describing the sexual maturation of bitterlings stated, “it may be a general rule that the larger the size attained, the slower the sexual maturity reached. Among the cyprinid fishes of Japan, all the acheilognathine species and the half of the rest of species attain sexual maturity within a year, and all others within more than two years. In two subspecies of Rhodeus ocellatus, the young born in early spring is capable to conduct reproductive function both in male and female, showing consequently two generation within a year.” As regards species of the genus Rhodeus, keeping in mind of their small size, their incomplete TRC state, which corresponds to a state at a juvenile stage in bitterlings having a complete TRC at an adult stage, reduction or absence of 'io 5', and two generations within a year, Rhodeus might have evolved from Tanakia or its ancestor by progenesis (Alberch et al., 1979; Buckup, 1993; Gould, 1977; Grande, 1994; Hosoya, 2001; Mabee, 1993; Miller, 1996; Myers, 1958; Webb, 1989a, 1989b; Weizman & Vari, 1988). This hypothesis does not contradict the proposed molecular phylogeny of bitterlings (Okazaki et al., 2001), which, in spite of a large morphological gap between Tanakia and Rhodeus, showed shorter genetic distance between Tanakia and Rhodeus than that between Tanakia and Acheilognathus.