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(Fig. 1a-3a, 6a)
Holotype (Fig. 1a). MRAC 87921, female, 166.1 mm SL; Democratic Republic of Congo : Wamba, riv. Maringa (00°11´ N 22° 28´E), H. Bertels, 8 November 1952 .
Paratypes . MRAC101372 (1 female), 220.7 mm SL, Democratic Republic of Congo : Bokuma (0°05´ S 18° 40´E), Rev. Hulstaert, 28 August 1955 . MRAC 79224-79225 (2 juveniles), 71.1-77.7 mm SL, Democratic Republic of Congo : Bokuma (0°05´ S 18° 40`E), Rev. Lootens, 1- 15 July 1952 . BMNH 1907.12.3.4 ( syntype of Polypterus retropinnis Vaillant, 1899 ZBK ), male, 205.3 mm SL, Republic of Congo : Diele de l`Alima (1°48´ S 14° 41´E), S. de Brazza. MNHN 1886-0297 ( syntype of Polypterus retropinnis Vaillant, 1899 ZBK ), male, 176.3 mm SL, Republic of Congo : Leketi, Alimamoyen (1°36´ S 14° 57´E), S. de Brazza. MRAC 72434-72435, 2, juvenile and male, 80.8-171.5 mm SL, Env. de Leopoldville (4°19´ S 15° 19 E), unknown date and collector.
Other material examined (non types). Democratic Republic of Congo ?: Ornamental fish imports from Kinshasa: ZSM 33572 (2), 168.5-184.8 mm SL, don. F. Schäfer (168.5 mm specimen appears in Fig. 2a). ZSM 33571 (3), 196.1-235.5 mm SL, don. F. Schäfer (196.1 mm specimen appears in Fig. 3a).
Diagnosis. Polyperus mokelembembe ZBK is distinguished from all other Polypterus ZBK species except P. retropinnis ZBK , P. teugelsi ZBK and P. palmas palmas by its high predorsal scale count (32-37 vs. 11-28). It differs from P. teugelsi ZBK by having 57-60 lateral-line scales (vs. 63-65), from Polypterus palmas palmas by a single large black blotch on pectoral fin base (vs. numerous small spots on posterior part of base), and from P. retropinnis ZBK in having a wider first dorsal finspine (6.4-8.1 vs. 4.6-6.1 % of HL), a shorter internostril distance (11.6-13.7 vs 14.3-18.0 % of HL), and fewer pectoral-fin rays (23-29 vs. 30-34) (Fig. 4). In addition, P. mokelembembe ZBK differs from all congeners by the presence of a few broad and ill defined lateral blotches or bars that converge dorsally to form broad saddles (vs. numerous black or brown bars or blotches, which may form a reticulate pattern but never converge dorsally to form a few broad saddles). There is no clear delimitation between the dark dorsolateral body coloration and the light coloured belly (vs. a clear border in P. retropinnis ZBK , P. teugelsi ZBK , P. palmas ZBK ssp., and P. weeksii ZBK ).
Description. See Figs. 1-3 for general appearance. Body subcylindrical and elongate, becoming increasingly laterally compressed over its caudal third. Greatest body depth on posterior half of body, approximately between first finlet and pelvic-fin base. Head slightly flattened dorsoventrally; mouth terminal; lips fleshy; snout comparatively acute and not broadly rounded as compared with all congeners except P. palmas polli . Anterior nostrils extending anteriorly as a nasal tentacle. Gill opening large, the opercular skin flap covering anterior portion of pectoral-fin base and extending from ventral midline to upper quarter of the body. Pectoral fins broadly rounded, almost circular, the posterior borders reaching the 8th or 9th scale row counted from behind the cleithrum but not reaching level of first dorsal spine. Six to eight dorsal finlets, of which the last one is continuous with the soft dorsal fin. Finlets overlapping when folded down. Membranous part of finlets supported by a strong and broad terminally bifurcated spine. Finlet membranes basally confluent with the following dorsal-fin spine base. Soft dorsal fin and caudal fin confluent. Caudal fin oval in shape or slightly lanceolate. Anal fin reaching beyond proximal base of caudal fin rays in both sexes. Anal fin enlarged in males and almost reaching level of end of caudal peduncle. Shape of visible part of ganoid body scales approximately square on flanks and rhomboid on caudal peduncle. The midlateral line originates from uppermost posterior margin of gill cover, extends down to a midlateral line position at end of pectorals, and continues to next to last or last scale on caudal peduncle. Slightly elongated lateral-line pores are located on anterior portion of each scale in the first half and in the central part of the second half of lateral line. Base of anal-fin rays and anus (located immediately anterior) covered by a sheath of distinct small scales, which are approximately twice as high as long. This scale sheath converges midventrally in front of the anus. Distance between pelvic and anal fin bases less than pelvic fin length. External gills retained in three juveniles examined: MRAC 79224 (71.1 mm SL) (gills 7.8 mm length), MRAC 79225 (77.7 mm SL) (gills 3.0 mm length), and MRAC 72434 (80.9 mm SL) (gills 2.5 mm length).
Color in alcohol. (Fig. 1a and 3a). Dorsal two thirds of body dark grey overall, with several broad and ill-defined dark grey to black bands and blotches. These dark blotches and bands may converge on dorsal third of body to form broad saddles on anterior half of body in front of first finlet. However, the melanin pattern appears to be more pronounced in juveniles than in adults. In adults the dark bands and blotches are sometimes barely discernable from the overall dark grey body coloration. There is no abrupt transition between the dark dorso-lateral body coloration and the light beige ventral coloration as in some other species (see Diagnosis). The fin membrane of each dorsal finlet has a distinct black blotch covering the upper two-thirds to three-fourths of the central membrane, which is otherwise of light beige color. Soft dorsal and caudal fins with vertical brown lines and dots arranged irregularly, resulting in a checkered appearance. Anal and pelvic fins light beige or dusky grey, either without markings or with a few brown markings. Pectoral-fin base with a prominent dark blotch on the posterior half, with the remainder of the fin base whitish or light beige (as on the belly). Pectoral fin in some specimens with three to four dark brown or grey concentric lines, either on a light beige or white background (e.g., as in the holotype) or on a dark grey background. In the latter case the bands are barely visible because of the low contrast. Head and preopercle dark grey or brown above the level of the pupil and white below. A prominent horizontal dark streak extending from below the eye to the lower jaw. Area between this streak and preopercle white. A second streak may be visible from below the eye to the preopercle. Lower lip white, with two lateral dark brown lines in some specimens. Tubular nostrils dark brown. Iris uniform olive or grey in well preserved specimens, including the holotype.
Coloration in life. Observations (based on five individuals: ZSM 33572 [two specimens: see Fig. 2] and ZSM 33571 [three specimens, all of which were observed alive for several weeks]). The overall color does not differ strongly from the pattern seen in preserved specimens, except that the whole body exhibits an olive-green hue. The edges of the preopercle, opercle, and frontal as well as of several smaller head bones are rimmed in black. The iris of living specimens consists of a broad bronze-colored inner ring and a narrow olive-colored outer ring.
Etymology. Named after Mokele-mbembe, a mythological creature believed by some to be a sauropod dinosaur that has survived the extinction of dinosaurs at the Cretaceous/ Tertiary boundary in the central Congo basin (Mackal, 1987). The name is chosen as an allusion to the archaic nature of polypteriforms, which most likely are the sister group to the remaining Actinopterygii (Patterson, 1982, Venkatesh et al, 2001, Inoue et al, 2003), and which probably existed at the same time as sauropods. A noun in apposition.
Distribution. Polypterus mokelembembe ZBK is known only from a few localities in the Congo basin, i.e. from the Alima drainage in the Republic of Congo, and the Maringa and Tshuapa drainage in the Democratic Republic of Congo. A third locality is labelled “environs de Leopoldville,” suggesting that it occurs in the vicinity of Kinshasa (See Fig. 5). The latter assumption is supported by information from ornamental fish exporters in Kinshasa, who claim that the new species is regularly collected in a blackwater stream east of Kinshasa at Kinkolé (C. Olungu, pers. comm.).
Remarks. The largest known specimen (ZSM 33571-3) is a female, 235.2 mm SL, that was selected from a commercial import. The second largest specimen is a female, 220.7 mm SL, (MRAC 101372 ) with several hundred eggs averaging approximately 1.5 mm diameter in both ovaries. The species has reproduced once in captivity (P. Bartsch, pers. comm.).