Petrocephalus

Lavoué, Sébastien, Sullivan, John P. & Arnegard, Matthew E., 2010, African weakly electric fishes of the genus Petrocephalus (Osteoglossomorpha: Mormyridae) of Odzala National Park, Republic of the Congo (Lékoli River, Congo River basin) with description of five new species, Zootaxa 2600, pp. 1-52 : 45-46

Key to the Petrocephalus species of Odzala

1 Fewer than 18 branched rays (rarely 18) in the dorsal fin; only eight to 10 scale rows between the anterior base of the anal fin and the lateral line; distinct melanin markings absent on the body (i.e., absence of black patches that are species-specific for many other Petrocephalus species); rosettes of Knollenorgan electroreceptors absent on the head ... ...................................................................................................................................... Petrocephalus microphthalmus

- Usually more than 20 dorsal fin branched rays (sometimes 20; in very rare instances 19); at least 10, usually more, scale rows between the anterior base of the anal fin and the lateral line; distinct melanin markings (black patches) may be present or absent on the body; electroreceptor rosettes present or absent on the head .................................... 2

2 Mouth large, its width at most 3.9 times in head length; at least 15 teeth in the upper jaw, usually more .................. 3

- Mouth small, its width at least 3.6 times (usually 4.0–4.4 times) in head length; usually fewer than 15 teeth in the upper jaw (rarely 15 or 16) ........................................................................................................................................... 5

3 Anal fin contains 26 or 27 branched rays; 20–22 branched rays in the dorsal fin; three intense black patches of melanin present on each side of the body: a rounded sub-dorsal mark, an ovoid caudal mark and a mark at the origin of the pectoral fin .............................................................................................................................. Petrocephalus balayi

- Anal fin contains more than 30 branched rays; more than 24 branched rays in the dorsal fin; only two distinct black patches of melanin on each side of the body: a sub-dorsal mark and a caudal mark ................................................... 4

4 Eye relatively small (HL/ED ≥ 4.0); mouth sub-terminal (HL/MP ≥ 4.4), opening under the anterior half of the eye; two distinct melanin marks present but sometimes pale: a rounded sub-dorsal mark and a crescent-like mark at the base of the caudal fin; Knollenorgan electroreceptors organized into three distinct rosettes on head, but rosettes relatively small; EOD waveform typical for the genus, polarity normal ( Fig. 10 C) ....................... Petrocephalus sauvagii

- Eye large (HL/ED ≤ 3.5); mouth sub-terminal but positioned more caudally along the ventral margin of the head (HL/MP ≤ 3.5), opening under the posterior half of the eye; two distinct melanin marks: a rounded, sometimes irregularly shaped, sub–dorsal black mark and a crescent-like black mark at the base of the caudal fin; three larger rosettes of Knollenorgan electroreceptors present on the head; EOD waveform very distinctive among congeners, appearing to be reversed in polarity compared to EODs of all other Petrocephalus species ( Fig. 11 C)........................ ................................................................................................................................... Petrocephalus pulsiverten s n. sp.

5 Anal fin contains 30 or more branched rays; melanin markings (black patches) present on the body and always distinctly visible................................................................................................................................................................. 6

- Anal fin contains at most 29 branched rays (usually fewer); melanin markings present but sometimes hardly visible ...................................................................................................................................................................................... 7

6 Dorsal fin contains 24–26 branched rays; eye large (HL/ED ≤ 3.2); mouth very small relative to many congeners (HL/MW ≥ 5.2); two melanin marks present and distinct but of medium intensity: a rounded sub-dorsal mark and a crescent-like mark at the base of the caudal fin; two readily observed rosettes of Knollenorgan electroreceptors present on the head (Augenrosette and Nackenrosette) plus a Kehlrosette that is rather difficult to observe without staining ........................................................................................................................................ Petrocephalus grandoculis

- Dorsal fin contains 24 (holotype) or fewer (Odzala specimens) branched rays; eye smaller in size (3.5 ≤ HL/ED ≤ 4.0); mouth larger (HL/MW ≤ 5.2); three distinct melanin marks (black patches) present: an ovoid sub-dorsal mark (sometimes small and covering few scales, but always intense), an ovoid caudal mark and a mark at the origin of the pectoral fin; all three electroreceptor rosettes present on the head and distinct ...................... Petrocephalus binotatus

7 Melanin markings on body intensely black with sharply defined edges, forming characteristic shapes (e.g., very rounded black sub-dorsal spot or saddle-like sub-dorsal patch, crescent shaped black mark at the base of the caudal fin or round black spot at the caudal fin base) .............................................................................................................. 8

- Melanin markings of much weaker intensity, consisting of more irregularly–shaped patches and with comparatively diffuse edges ............................................................................................................................................................... 10

8 Small but intense black mark present on each side of the body at the pectoral fin origin; Knollenorgan electroreceptors on the head may or may not be arranged into discrete clusters (i.e., rosettes may be present or absent), but if rosettes are present the Augenrosette is always as well developed as the other rosettes.............................................. 9

- No distinct black mark visible at the origin of the pectoral fin; electroreceptors organized into three distinct rosettes on the head, but the Augenrosette is small and not as well developed as the other rosettes ...... Petrocephalus christyi

9 Eye large (HL/ED ≤ 3.3); sub-dorsal black patch often contacting the contralateral mark over dorsum and most anterior branched rays of the dorsal fin; caudal melanin marking forming a rather uniformly shaped crescent (or "V") that extends onto the upper and lower fleshy lobes of the caudal fin; Knollenorgan electroreceptors on the head are

not clustered into discrete groups (i.e., rosettes absent)...................................................... Petrocephalus zakoni n. sp. - Eye small (HL/ED ≥ 3.7); sub-dorsal black patch distinctly rounded, never in contact with the contralateral mark and not extending onto the dorsal fin; caudal mark ovoid rather than crescent- or V-shaped, not extending onto the upper and lower parts of the caudal fin; Knollenorgans on the head are clustered into three rosettes........................... ................................................................................................................................... Petrocephalus odzalaensis n. sp.

10 Mouth sub-terminal, opening under the anterior half of the eye; snout short (HL/SNL ≥ 6.5); Knollenorgan electroreceptors on the head are clustered into three rosettes (but a distinctive Kehlrosette is difficult to observe without staining); EOD of normal polarity, often appearing to have an overall biphasic waveform at low gain, although a minute third peak is in fact present (first head-positive peak, P1, much larger in amplitude than second head-positive peak, P3, which never exceeds 10% of total peak-to-peak amplitude) ........................... Petrocephalus valentini n. sp.

- Mouth sub-terminal but positioned more caudally along the ventral margin of the head, opening under the posterior half of the eye; snout somewhat longer (HL/SNL = 5.4 in the single specimen available, the holotype); Knollenorgans on the head are clustered into only two rosettes (the Nackenrosette and the Kehlrosette), Augenrosette absent; EOD of normal polarity, with more than two phases apparent even at low gain (the only specimen of this species that has been recorded exhibits an EOD containing 4 peaks; the second head-positive peak, P3, is larger in amplitude than the first head-positive peak, P1; amplitude of P3 substantially greater than 10% of total peak-to-peak amplitude) ................................................................................................................................ Petrocephalus mbossou n. sp.

Figures

FIGURE 10. Petrocephalus sauvagii of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Photograph of a live specimen (no scale). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).

FIGURE 11. Petrocephalus pulsivertens n. sp. of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Photograph of a live specimen (no scale). B. Photograph of the preserved holotype (CU 88085; scale bar = 1.0 cm). C. EOD waveforms. One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings (N = number of individuals). All EODs are scaled to the same peak-to-peak voltage, and they are plotted (head-positive up) on the same time scale as overlays centered on the largest positive peak of each waveform (scale bar = 0.2 msec).