Petrocephalus pulsivertens, Lavoué, Sébastien, Sullivan, John P. & Arnegard, Matthew E., 2010

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 : 32-35

Petrocephalus pulsivertens n. sp.

[Odzala field identification and in Lavoué et al (2008): Petrocephalus sp. 9, OTU 9]

Images. Fig. 11 A, photo of a live specimen from Odzala and Fig. 11 B, photo of the preserved holotype (CU 88085).

Type material. Holotype, CU 88085 (morpho, DNA), male, 114.8 mm SL. Republic of the Congo, small channel around island in Lékoli River ( Congo basin), Odzala National Park, (0.62 ° N, 14.95 ° E), V. Mbossi, J.P. Friel, S. Lavoué & J.P. Sullivan coll., 16 August 2002.

Paratypes. AMNH 251418 (ex CU 88096) (morpho, EOD), male, 99.9 mm SL; CU 88097 (morpho, EOD, DNA; caudal peduncle dissected by Lavoué et al. (2008) to sample electric organ for histological examination), sex undet., 95.0 mm SL; AMNH 251419 (ex CU 88098) (morpho, EOD), sex undet., 103.2 mm SL. Republic of the Congo, small channel around island in Lékoli River ( Congo basin), Odzala National Park, (0.62 ° N, 14.95 ° E), J.P. Friel, S. Lavoué & J.P. Sullivan coll., 20 August, 2002. CU 87839 (morpho, EOD, DNA), male, 87.3 mm SL; CU 89188 (morpho), sex undet., 98.5 mm SL; CU 89188 (morpho, caudal peduncle dissected by Lavoué et al. (2008) to sample electric organ for histological examination, sex undet., 103.6 mm SL; CU 89188 (morpho), male, 107.4 mm SL; CU 89188 (morpho), male, 86.1 mm SL. Republic of the Congo, small channel around island in Lékoli River ( Congo basin), Odzala National Park, (0.62 ° N, 14.95 ° E), V. Mbossi, J.P. Friel, S. Lavoué & J.P. Sullivan coll., 16 August 2002.

Other specimens. We examined five other specimens from Odzala National Park and one from the Sangha River basin (specimen list provided in the section "additional material examined").

Diagnosis. Petrocephalus pulsivertens n. sp. is distinguished from all other Petrocephalus species in Central Africa by the following combination of characteristics. Dorsal fin with at least 25 branched rays (range = 25–27). Anal fin with at least 31 branched rays (range = 31–35). Mouth large (HL/MW ≤ 3.7, range = 3.0–3.7). Fifteen to 21 teeth in the lower jaw; 24–30 teeth in the upper jaw. Eye large (HL/ED ≤ 3.5, range = 3.2–3.5). Pigmentation pattern consists of two distinctive melanin markings (black patches): (1) a distinct ovoid mark below the anterior base of the dorsal fin; and (2) a crescent-like mark, sometimes diffuse, centered at the base of the caudal fin and extending onto the upper and lower parts of the caudal fin. EOD appears to be inverted in polarity, with a first main phase that is negative under the standard recording geometry, resulting in a waveform that is very distinctive in comparison to all known congeners.

Description. Morphometric ratios and meristic data for the holotype and paratypes are presented in Table 9 . Petrocephalus pulsivertens n. sp. is a relatively large sized species within the genus Petrocephalus (maximum SL observed = 114.8 mm, the length of the holotype). Body ovoid, longer than high (2.6 ≤ SL/H ≤ 2.9, paratype average = 2.7, holotype = 2.8) and laterally compressed. Head length between 3.6 and 3.7 times in standard length (holotype = 3.7). Eye large (3.2 ≤ HL/ED ≤ 3.5, paratype average = 3.4, holotype = 3.5). Snout short (6.1 ≤ HL/SNL ≤ 7.3, paratype average = 6.5, holotype = 6.8) and round. Mouth large (3.0 ≤ HL/ MW ≤ 3.7, paratype average = 3.3, holotype = 3.0), sub-terminal, opening just under the anterior half of the eye. Teeth bicuspid, small and numerous, 15–21 (paratype average = 18, holotype = 21) in a single row in the upper jaw, 24–30 (paratype average = 28, holotype = 29) in a single row in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (1.6 ≤ SL/PDD ≤ 1.7 and 1.7 ≤ SL/PAD ≤ 1.8, respectively). Predorsal distance equal to, or slightly greater than, pre-anal distance (1.0 ≤ PDD/PAD ≤ 1.1). Dorsal fin with 25– 27 branched rays (paratype median = 26, holotype = 26). Anal fin with 31–35 branched rays (paratype median = 33, holotype = 34). Scales cover the body, except for the head. Lateral line visible and complete with 38–40 pored scales along its length. Caudal peduncle relatively thin (2.1 ≤ CPL/CPD ≤ 2.3, holotype = 2.2). Twelve scales around the caudal peduncle. Skin on head thick, becoming opaque with formalin fixation. Knollenorgan electroreceptors on head clustered into three distinct rosettes.

Holotype (m) Paratypes (n=8)

Min–Max Mean Std–Dev Min–Max Median

Meristic counts:

Number of scale rows between the anterior base of 14 13–15 14 the anal fin and the lateral line (SDL)

Number of teeth in the upper jaw (TUJ) 21 15–21 18 Number of teeth in the lower jaw (TLJ) 29 24–30 28 Live coloration ( Fig. 11 A). Body and head mostly whitish-silvery, but head also exhibits faint metallic blue-purple iridescence. Dorsum darker than the rest of the body. Melanin patterning consists of two distinct black marks: (1) a distinct ovoid melanin mark below the anterior base of the dorsal fin on each side of the body and (2) a crescent-like melanin mark, sometimes diffuse, centered at the base of the caudal fin on each side and extending onto the upper and lower parts of the caudal fin. No black mark is present at the base of the pectoral fins. The fins themselves are mostly translucent, with the dorsal and caudal fins sometimes turning slightly yellow after formaldehyde preservation.

Distribution ( Fig. 1 ). Endemic to the Congo River basin. We collected P. pulsivertens n. sp. along the main course of the Lékoli River. This species seemed to be absent from the small tributary creeks flowing through forest or savannah when we surveyed Odzala National Park. Elsewhere, P. pulsivertens n. sp. occurs in the vicinities of Brazzaville (i.e., the Pool Malebo), the Dja River ( Cameroon) and the Dzangha-Sangha region (Sangha River basin, Central African Republic) (pers. obs.), although no EOD recordings have been made of this species outside Odzala.

Electric organ discharge ( Fig. 11 C). The EOD waveform of P. pulsivertens n. sp., which is known only from our recordings in Odzala, resembles an inverted-polarity version of the "typical" Petrocephalus EOD. That is, the temporal sequence of electrocyte face firing known for all other Petrocephalus (i.e., firing of the posterior electrocyte face preceding firing of the anterior electrocyte face) appears to be reversed in P. pulsivertens . At high gain, however, one can see that the very first event in the EOD is a minute head-positive deflection (for an example see Fig. 3 D of Lavoué et al., 2008). This waveform feature is consistent with current from the stalks of the posterior electrocyte face (and possibly early current during the beginning of posterior face firing itself) slightly preceding anterior face firing. Despite the waveform inversion, histological examination of electrocytes of P. pulsivertens n. sp. reveals them to be type "NPp," the character state also shared by all other Petrocephalus species investigated to date. We suspect that part of the mechanism underlying the reversed ordering of major peaks in the EOD of P. pulsivertens n. sp. might involve changes in firing threshold for one or both electrocyte faces (as proposed in Lavoué et al., 2008). This interesting example of waveform inversion in Petrocephalus reminds us that careful attention must be paid to the geometry of electrodes during EOD recordings from unknown mormyrid faunas. Given its inverted-polarity appearance, the EOD of P. pulsivertens n. sp. is immediately recognizable as distinct from those of all other congeners. Based on a threshold of 1.5% of peak-peak amplitude (and at ambient recording temperatures), the duration of the EOD of P. pulsivertens n. sp. ranges from 0.270 to 0.418 msec, falling in the range of many "typical" Petrocephalus EODs. Statistics for waveform landmarks and other EOD measurements are provided by Lavoué et al. (2008).

Etymology. From the Latin " pulsus," impulse, beating; and from " vertere, " to turn, exchange. The name describes the unusual EOD waveform of P. pulsivertens n. sp. The inverted appearance of this species’ EOD is unique among all Petrocephalus recorded to date.

Figures

FIGURE 1. Map of Africa (right) showing the entire Congo River and its main tributaries together with the neighboring Lower Guinea province (first inset at center). The boundary between the Congo and Lower Guinea provinces is shown by a dashed line. Filled black circles indicate type localities for all Petrocephalus species that were described from either province and were considered valid just prior to the present study. Exact type localities are unknown for P. b a l a y i and P. sauvagii. Based on our understanding of the chronology of Central African exploration at the time of the descriptions, we estimate these type localities to be the following: the vicinity of Pool Malebo on the Lower Congo River near the modern cities of Brazzaville and Kinshasa [4.25 ° S, 15.29 ° E] for P. sauvagii; and the vicinity of the present-day city Lambaréné on the Lower Ogooué River [0.7 ° S, 10.22 ° E] for P. b a l a y i. Second inset at the far left: detailed map of Odzala National Park, located in the Congo River basin. Within the boundaries of the park, forest is shown in green and savannah in yellow. The red oval indicates our collection area (a segment of the Lékoli drainage system, including the lower parts of two of its tributaries, the Pandaka and Lékénie Rivers).

FIGURE 3. Petrocephalus binotatus of the Lékoli River system of Odzala National Park, Republic of the Congo. A. Photograph of a live specimen (no scale: the photo has been maximally enlarged to better illustrate details of body shape, melanin patterning, etc.). B. Photograph of a preserved specimen (scale bar = 1.0 cm). C. EOD waveforms displayed separately for obvious males and other individuals (see text). One EOD was arbitrarily selected from each recorded individual and superimposed with the other recordings (N = number of individuals, given separately for obvious males and all other 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).

Tables

TABLE 9. Principal morphometric ratios and meristic counts for the holotype (CU 88085) and eight paratypes (CU 88097, CU 87839, CU 89188, AMNH 250932, AMNH 250933) of Petrocephalus pulsivertens n. sp. (Abbreviations: m = male; Std – Dev = standard deviation; Min – Max = minimum – maximum).

Standard length (mm)	114.8	86.1–107.4	97.6	7.7
Head length (mm)	30.9	23.5–30.9	26.6	2.1
Ratio of standard length (SL):
SL/body height (H)	2.8	2.6–2.9	2.7	0.1
SL/head length (HL)	3.7	3.6–3.7	3.7	0.1
SL/pre-dorsal distance (PDD)	1.6	1.6–1.7	1.6	0.0
SL/pre-anal distance (PAD)	1.7	1.7–1.8	1.7	0.0
SL/dorsal fin length (DFL)	4.3	3.9–4.3	4.1	0.1
SL/anal fin length (AFL)	3.2	2.9–3.3	3.1	0.1
SL/caudal peduncle length (CPL)	6.5	6.8–6.1	6.6	0.2
SL/mouth width (MW)	11.1	11.1–13.8	12.2	0.8
Ratio of head length (HL):
HL/snout length (SNL)	6.8	6.1–7.3	6.5	0.4
HL/mouth width (MW)	3.0	3.0–3.7	3.3	0.2
HL/eye diameter (ED)	3.5	3.2–3.5	3.4	0.1
HL/interorbital width (IOW)	3.1	2.9–3.4	3.1	0.2
HL/head width (HW)	1.8	1.8–2.0	1.9	0.1
HL/mouth position (MP)	3.3	3.0–3.5	3.3	0.2
Ratio of caudal peduncle length (CPL):
CPL/caudal peduncle depth (CPD)	2.2	2.1–2.3	2.1	0.1