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The species name retropinnis ZBK has been applied, in the scientific literature (Gosse, 1988, Britz, 2004), both to specimens conspecific with Bertin´s “holotype” (of P. retropinnis ZBK ) and to specimens conspecific with the two remaining syntypes. Despite Bertin´s listing of the “holotype,” as well as a similar listing in Eschmeyer (1998:1443; and online catalogue), there is no indication that Vaillant designated a holotype in his original description of Polypterus retropinnis ZBK . Although Bertin's subsequent action could be interpreted as a lectotype designation, this runs counter to ICZN Article 74.5, which states that, for lectotype designations made before 2000, either the term “lectotype” or “the type” must be used. The article further states that “when the original work reveals that the taxon had been based on more than one specimen, a subsequent use of the term “holotype” does not constitute a valid lectotype designation ...” In order to firmly establish the species name retropinnis ZBK , specimen MNHN 1886-295 is accordingly designated the lectotype of Polypterus retropinnis ZBK , and a rediagnosis of the species is included in this paper. The lectotype designation of this specimen follows recommendations 74A and 74B for Article 74.7 of the ICZN (1999), because this largest specimen of the type series is the first specimen that was illustrated (Boulenger, 1909), and because Bertin (1940) had referred to this specimen as the “holotype”. Although the latter act was nomenclatorially invalid, the intended restriction was implicitly accepted later by Britz (2004: 185), who listed specimen MNHN 1886-295 as “holotype,” and listed and illustrated specimen MNHN1886-297 as “paratype” (Britz, 2004: 184-185).
The following rediagnosis of P. retropinnis ZBK is provided since the type series of P. retropinnis ZBK originally consisted of two species, one of which is herein described as P. mokelembembe ZBK . See Figs. lb-3b for general appearance. Polypterus retropinnis ZBK is distinguished from all other species of Polypterus ZBK except P. mokelembembe ZBK , P. ornatipinnis ZBK , P. teugelsi ZBK and P. palmas ZBK ssp. in having a high predorsal-scale count (26-34 vs. 11-25). It differs from P. ornatipinnis ZBK , P. teugelsi ZBK and P. p. polli in having 57-60 lateral-line scales (vs. 61-65 in P. ornatipinnis ZBK and P. teugelsi ZBK and 52-55 in P. p. polli ), from Polypterus p. palmas and P. p. buettikoferi by having a single large black blotch on the pectoral-fin base (vs. numerous small spots on posterior part of base), and from P. mokelembembe ZBK by having a narrower first dorsal fin-spine (4.6-6.1 vs. 6.4-8.1 % of HL), a greater internostril distance (14.3-18.0 vs. 11.6-13.7 % of HL), and more pectoral-fin rays (30-34 vs. 23-29). In addition, living specimens of P. retropinnis ZBK differ from all congeners in their iris coloration, which consists of creamy white areas and black dots alternating with each other around the iris. However, this character state is rarely visible in preserved specimens.
Remarks on the juvenile coloration of P. retropinnis ZBK (Fig. 6). For different species of Polypterus ZBK , juvenile coloration (where known) may or may not differ strikingly from adult coloration (Boulenger, 1902, Britz & Bartsch, 1999), but tends to be brighter and more contrasting as compared with large specimens. In Polypterus mokelembembe ZBK , the smallest specimen available (MRAC 79224) already exhibits the adult coloration. In contrast, the coloration in juvenile Polypterus retropinnis ZBK differs strikingly from the adult coloration. In very small specimens (TL up to approx. 50 mm) the body is uniformly brown, with many light spots, whereas in larger specimens there is a pattern of dark crossbars on the back, with light interspaces. These crossbars merge with two to three narrow and ill-defined midlateral longitudinal stripes. At this stage, three dark horizontal stripes are present on the head, of which the uppermost and median stripes start immediately behind the eye and the lowermost starts below the bottom of the orbit. Remnants of the last stripe are retained in the adult coloration to form the “tearstripe,“ which is characteristic of many Polypterus ZBK species (see Schäfer  for additional photographs).