Melanorivulus pictus ( Costa, 1989 )

Deprá, Gabriel De Carvalho, Silva, Hugmar Pains & Graça, Weferson Júnio Da, 2017, A new pelvic-less species of Melanorivulus Costa (Cyprinodontiformes: Cynolebiidae), with a discussion on the pelvic-fin absence in killifishes, Zootaxa 4300 (1), pp. 111-124 : 117-120

Melanorivulus pictus ( Costa, 1989)

( Fig. 5 )

Rivulus pictus Costa, 1989: 525 -527, figs. 2, 2a (Type locality, “córrego Fumal no cruzamento com a rod. Brasília-Distrito Federal, Brasil ”; original description; key); Costa, 1995: 208, 212–216 (key; redescription); Costa, 2003: 542 (synonymic list, maximum length, distribution); Costa, 2005: 71 (key); Costa, 2006: 161, 175 (inclusion in subgenus Melanorivulus ; osteology; phylogenetic analysis).

Melanorivulus pictus: Costa, 2011: 241 (inclusion in genus Melanorivulus ; phylogenetic analysis).

Comments. The re-examination of the type series of Melanorivulus pictus revealed that one paratype (MNRJ 11551, female; Fig. 5 a) lacks the pelvic fin from both sides. This fact was overlooked in the original description (which was based in 22 specimens; Costa, 1989), and in all subsequent papers on Melanorivulus . In fact, the only species that was known, until now, to lack the pelvic fin is M. planaltinus , in which the presence of the pelvic fin is also polymorphic ( Costa & Brasil, 2008). Although it was not possible to examine the aforementioned paratype for the presence of the pelvic girdle, 2 c&s specimens examined herein proved to be devoid of this bone, as well as of the fin itself. These specimens belong to a population found not far from the type locality. Within this population (363 specimens available, not including those smaller than 8.0 mm SL, in which the pelvic fin is not formed yet), 300 (82.6%) present two pelvic fins, 14 (3.8%) present a single pelvic fin and 49 (13.4%) present no pelvic fins. Pelvic-fin length was measured from 115 specimens presenting both fins, to verify whether the pelvic-fin length is a normally distributed character and to examine its allometry ( Fig. 6 ). The pelivc-fin length was also measured for 6 specimens with a single pelvic; all but one presented a relatively small fin, which averaged 71.7% (standard deviation 0.25) of the length predicted by the regression in Fig. 6 . Among c&s specimens of M. pictus , two have both pelvic fins. One has six rays on either side, and the other has seven. The only c&s specimen with only one, atrophied pelvic fin, has only four rays.

The first reference to the frontal squamation pattern of Melanorivulus pictus was presented by Costa (1995a: 213), who mentioned that the species exhibits both the E and F patterns. However, as already mentioned, Costa (1995) mixed samples of several species in his account of M. pictus . Costa (2005: 70–71, key) distinguished M. pictus from all other congeners by a combination of characters including E-patterned frontal scales. Costa & Brasil (2008) mentioned that M. pictus shares with M. planaltinus similar meristic characters, but considered that the latter exhibits only E-patterned frontal squamation. However, of ten Melanorivulus pictus specimens examined herein for the frontal squamation pattern, only four have typical E-patterned scales; two have a typical F pattern; one has an E pattern on one side of the head and a F pattern on the other; one has, also contralaterally, F and D patterns; one has a D pattern on each side; and one has no pattern at all, because there is no scale that is not overlapped by at least one other scale. Given the fact that M. nelsoni also exhibits a wide range of frontal squamation patterns, we suggest that this character should not be given much importance in distinguishing among Melanorivulus species.

Material examined. M. pictus . MNRJ 11550, 1 , 24.0 mm SL, male, holotype of Rivulus pictus , Brazil, Distrito Federal, Brasília, córrego Fumal ( rio São Bartolomeu / rio Corumbá basin), c. 15°35′S, 47°40′W; L. E. M. Cardoso, 18 Apr 1981 . MNRJ 11551, 2 , 23.1–24.6 mm SL, paratypes of Rivulus pictus , same data as MNRJ 11550 . MZUEL 12834, 108, 4.2–25.6 mm SL. MZUEL 12835, 101, 6.7–24.2 mm SL. MZUEL 12836, 101, 5.0– 22.1 mm SL. MZUEL 12838, 111 , 8.3–24.3 mm SL (4&s): Brazil, Distrito Federal, Brasília, stream tributary to the ribeirão Bananal ( rio São Bartolomeu / rio Corumbá basin), c. 15°43′S 47°53′W.

Figures

FIGURE 5. Melanorivulus pictus: (a) paratype, MNRJ 11551, 24.0 mm SL, female; (b) holotype, MNRJ 11550, 24.0 mm SL, male; (c) MZUEL 12835, 23.0 mm SL, male; (d) MZUEL 12835, 21.6 mm SL, female; (e) MZUEL 12835, 14.3 mm SL, juvenile.

FIGURE 6. Polynomial regression showing the relationship between standard length and pelvic-fin length in M. pictus.