Paramormyrops jacksoni, JACKSONI (POLL, 1967)

Rich, Madeline, Sullivan, John P. & Hopkins, Carl D., 2017, Rediscovery and description of Paramormyrops sphekodes (Sauvage, 1879) and a new cryptic Paramormyrops (Mormyridae: Osteoglossiformes) from the Ogooué River of Gabon using morphometrics, DNA sequencing and electrophysiology, Zoological Journal of the Linnean Society 180, pp. 613-646 : 625

PARAMORMYROPS JACKSONI ( POLL, 1967)

Marcusenius jacksoni Poll, 1967: 55 , Fig. 14 . Holotype: Dundo Museum 5575 (unique). Type locality: Nharicumbi village , 12°S, 21°10′E, Longa River tributary of Luena River (Zambesi River basin), Angola.

Paramormyrops jacksoni – Taverne et al., 1977: 640.

Note: Because Paramormyrops jacksoni is known from a single specimen from a tributary of the upper Zambezi River in Angola, well outside Lower Guinea and Congo River basins where all other Paramormyrops are found, it is likely that this species was incorrectly reassigned to Paramormyrops by Taverne et al. (1977). Instead it more probably belongs in Pollimyrus . This opinion is shared by D. Tweddle and P.H. Skelton (pers. comm.) who have examined specimens of Pollimyrus from the Kataba tributary of the Upper Zambezi in neighboring Zambia that are a close match to P. jacksoni in meristics, body form, and coloration. Further studies are needed before making a generic reassignment of P. jacksoni .

Figures

Figure 1. (A) Paramormyrops sphekodes (Sauvage, 1877) MNHN A.893 photographed in 1984 by W. Harder at which time the lot contained two specimens, suspended vertically in a tall jar from a glass floater. The original MNHN catalogue shows two specimens accessioned in 1878 under this number. The larger specimen (SL = 113.8 mm) is currently catalogued as A 893; the smaller specimen (SL = 98.7 mm) was subsequently catalogued in 1998 as MNHN 1050-1998. Sauvage’s original description indicates multiple specimens with a largest of 140 mm total length, but he designated no holotype. We regard these specimens as syntypes prior to our designation of the larger as lectotype. (B) Radiograph of MNHN A893.

Figure 2. Electric organ discharge (EOD) waveforms recorded from 40 specimens of P. sphekodes-like mormyrids from the Ogooué River Basin of Gabon suggest the possibility of two species with distinct EOD waveforms. (A) For each specimen, EOD duration is plotted against standard length (SL). (B) Histogram of EOD durations reveals two modal peaks: one for short EODs, <2 ms duration, and one for longer EODs,> 2 ms. (C) EOD waveforms of longer (above) and shorter duration (below) are superimposed after each EOD’s amplitude is normalized to the same peak-to-peak height and centred on the zero-crossing between positive and negative peaks. Blue lines are males and red lines are females. Head positivity is upward. EOD duration is measured between T1 and T2 (in E), first and last points of the waveform that deviate above or below the baseline by more than 2% of the peak-to-peak height. In previous publications, the longer EOD type was referred to by the code name ‘SN4’. The fish with the ‘short EOD’ waveform is new to this study. (D) Histograms of SLs of all 40 specimens separated by EOD-type and by sex/age class show that within each EOD type there are males recognized by their dimorphic anal fins.Within each group, males tend to have the longest duration waveforms.This sex difference is especially pronounced for SN4 males recorded during the breeding season. Fish of both EOD types co-occur at two sites in Gabon: the main channel of the Ogooué River at Doumé and the Sébé River nearby (see map). (E) EOD waveform of specimen CUMV 98177 tag JPS-1238 showing how EOD duration is measured.

Figure 3. The Paramormyrops specimens with short EODs, and those called SN4 have overlapping meristics but differ in a number of morphometric ratios. Here, the short EOD specimens are shown as blue circles, while ‘*’ indicates the lectotype of P. sphekodes and ‘+’ indicates the paralectotype. The red circles show those with longer EODs referred to as SN4 specimens. The short EOD forms have elevated ratios of interorbital width to snout length and correspondingly blunter snout angles than the SN4 specimens. They also have slightly reduced caudal peduncle depth to length ratios. There is overlap in each ratio taken separately, but combined they provide a convenient morphological basis for diagnosis between these two EOD types. EOD traces are 10 ms long.

Figure 4. The short EOD and SN4 Paramormyrops differ in the ratio of head length (HL) to head depth (HD) when measurements are taken from radiographs. (A) HLx/HDx is plotted against standard length for 41 specimens including short EOD specimens (n = 9, blue circles), SN4 specimens (n = 30, red squares) and the two existing types (* = lectotype of P. sphekodes and ‘x’ = the paralectotype). Solid lines show linear regression lines showing that head shape changes little with overall size. The measurements of the lectotype (LT) of P. sphekodes (MNHN-A893) and paralectotype (PLT) (MNHN 1998-1050) identify the short EOD individuals as P. sphekodes. The specimens with SN4-type EODs belong to a new species (red * indicates the new species holotype). Specimen 1185 is shown in x-ray in C. (B) Non-overlapping histograms of HLx/ HDx allow for good diagnosis of the two EOD types even if no EOD is available, as with the two types of P. sphekodes. (C) Radiographs of two specimens (Specimen CUMV 98134 tag number JPS-1185, an SN4 fish and MNHN-A893) illustrate landmarks used for measuring HLx and HDx (see Material and Methods). Scale bars = 1 cm.