Petrocephalus squalostoma ( Boulenger, 1915 )

Lavoué, Sébastien, 2012, Petrocephalus Marcusen, 1854 (Osteoglossomorpha: Mormyridae) of the Bangweulu-Mweru ecoregion (Luapula River system, Congo basin), with the description of a new species, Journal of Natural History (J. Nat. Hist.) 46 (35 - 36), pp. 2159-2178 : 2164-2170

Petrocephalus squalostoma ( Boulenger, 1915)

(Figures 2A–C; 3C)

Marcusenius squalostoma Boulenger, 1915: 163 .

Pollimyrus squalostoma ( Boulenger, 1915) : Taverne (1971): 105. (Revised definitions and contents of several mormyrid genera, including Marcusenius , with the creation of two genera, Pollimyrus and Brienomyrus )

Petrocephalus squalostoma ( Boulenger, 1915) : Taverne (1972): 162. (Descriptive work on the osteology of several mormyrid genera followed by comments on the evolution of the Mormyridae with a revised classification)

Type specimens

Syntypes. BMNH 1920.5 .26.1 (two syntypes, two examined) , MRAC 14352–54 (three syntypes, one examined); Zambia, Congo basin, Lake Mweru , a tributary of the Lukinda River (currently known as the Lunchinda River), a tributary of Lake Mweru (estimated 8.51 ◦ S, 28.96 ◦ E, see Figure 1 ); coll. L. Stappers and M.G. Dhont-De Bie .

Diagnosis

Petrocephalus squalostoma is distinguished from all other Petrocephalus species of the Congo province by the following combination of characteristics: body coloration pattern without intense melanin mark, sometimes a faded subdorsal roundish mark present; short dorsal fin with 15–22 branched rays (median 20) and 27–32 branched rays in the anal fin (median 29); more than 13 scale rows between the anterior base of the anal fin and the lateral line; three distinct electroreceptive rosettes in the head.

Description

Morphometric ratios and meristic data for three syntypes and 23 non-type specimens are detailed in Table 1. Petrocephalus squalostoma is a medium-sized species within the genus (maximum SL observed = 121.7 mm). Body ovoid, longer than high (mean SL/H = 3.3) and laterally compressed. Head length 3.9 times (mean) in standard length. Snout short (mean HL/ SNL = 6.4) and round. Mouth relatively small (mean HL/ MW = 4.0), sub-terminal, opening under the posterior half of the eye. Teeth small and bicuspid, a median of 11 teeth in a single row in the upper jaw, a median of 19 teeth in a single row in the lower jaw. Dorsal and anal fins originate in the posterior half of the body (mean SL/ PDD = 1.6 and mean SL/ PAD = 1.7). Pre-dorsal distance slightly greater than the pre-anal distance (1.0 ≤ PDD/PAD ≤ 1.1). Median dorsal fin branched rays of 20. Median anal fin branched rays of 29. Scales cover the body, except for the head. Lateral line visible and complete, a median count of 40 pored scales along its length. Median scales of 15 between the anterior base of the anal fin and the lateral line. Caudal peduncle thin (mean CPL / CPD = 2.6). Skin on head thick, turning opaque with formalin fixation, masking the eyes (see Figure 2A). Knollenorgans visible, clustered into the three distinct rosettes of Harder (1968).

Petrocephalus squalostoma differs from Petrocephalus grandoculis Boulenger, 1920 and Petrocephalus sauvagii (Boulenger, 1887) by its fewer number of branched rays Figure 2. Photographs of preserved specimens of Petrocephalus squalostoma from the Bangweulu-Mweru ecoregion, Luapula River system, Congo basin. (A) Preserved specimen (CU 91141, scale bar 1.0 cm) (photo by John P. Sullivan, CUMV). (B, C) Two syntypes (BMNH 1920.5.26.1, same scale bar as in A) (© The Natural History Museum, London).

in the dorsal fin (median = 25, range 24–26 in P. grandoculis and median = 28, range 26–30 in P. sauvagii ) and anal fins (median = 31, range 30–32 in P. grandoculis and median = 35, range 33–38 in P. sauvagii ) but Petrocephalus squalostoma differs from Petrocephalus hutereaui (Boulenger, 1913) by more branched rays in the dorsal and anal fins (16 and 25 in P. hutereaui , respectively). Petrocephalus squalostoma differs from P. c. haullevillii , P. c. congicus , Petrocephalus mbossou Lavoué, Sullivan and Arnegard, 2010 , Petrocephalus microphthalmus Pellegrin, 1908 , Petrocephalus schoutedeni Poll, 1954 , Petrocephalus valentini Lavoué, Sullivan and Arnegard, 2010 , and Petrocephalus zakoni Lavoué, Sullivan and Arnegard, 2010 by the presence of three very distinct Knollenorgan-type clusters in the head. Petrocephalus squalostoma can be further distinguished from P. simus by its mouth opening under the posterior half of the eye (versus the anterior half of the eye in P. simus ) and its relatively larger mouth (HL/MW = 4.0, range 3.6–4.5 versus 5.3, range 4.4–7.3 in P. simus ). Finally, P. squalostoma can be further distinguished from P. c. catostoma by its number of scales around the caudal peduncle (12 versus 15/ 16 in P. c. catostoma ) ( Kramer and van der Bank 2000).

Live coloration

Body background mostly silver-white/gold with metallic reflections, darker dorsally from the snout to the caudal peduncle ( Figure 3C ). Absence of melanin mark in most specimens. In a few specimens presence of a pale subdorsal roundish mark lying below the anterior base of the dorsal fin, on each side of the body. All fins whitish-yellowish, mostly translucent with fine black pigmentation on the lepidotrichia.

Petrocephalus squalostoma differs from Petrocephalus balayi Sauvage, 1883 , Petrocephalus binotatus Pellegrin, 1924 , Petrocephalus christyi Boulenger, 1920 , P. mbossou , Petrocephalus odzalaensis Lavoué, Sullivan and Arnegard, 2010 , Petrocephalus pulsivertens Lavoué, Sullivan and Arnegard, 2010 , and P. zakoni by the absence of any distinct black marking on the body.

Distribution

The five syntype specimens of P. squalostoma collected from a small northern tributary of Lake Mweru; the present collection extends the distribution of P. squalostoma to the Luongo River, the Upper Lualupa River downstream to Lake Bangweulu, Lake Bangweulu, and as far as the Chambeshi River ( Figure 1 ).

Electric organ discharge

Unknown. Electrocyte anatomy not examined.

Remarks

The cytochrome b analysis reveals two distinct genetic groups of P. squalostoma : a “Chambeshi River/Lake Bangweulu” group and a “Luongo River/Kalungwishi River” group ( Figure 4 ). No morphological differentiation was found to support this genetic differentiation. The type specimens from the Lukinda stream ( Figure 1 ) are also notable in having comparatively few dorsal and anal fin rays compared with the other specimens ( Table 1).

Other specimens examined

Zambia, Congo basin. CU 91141; Luapula River, Central Luapula River at Luapula River Bridge (12.11 ◦ S, 29.85 ◦ E) (station JPF 05-006); coll. Bills, Chilala and Friel , 22 September 2005 (five specimens including one sexually mature male, 65.3–74.0 mm SL) (CU DNA tissues: 40 and SAIAB DNA tissue: 39). CU 91142; Luapula River, Lwela River at bridge on road from Mansa to Kafwanka Lwela River (11.56 ◦ S, 29.17 ◦ E) (station JPF 05-010); coll. Bills, Chilala and Friel, 22 September 2005 (one sexually mature male, 68.5 mm SL) (CU DNA tissue 62 and SAIAB DNA tissue 63). CU 91145; Luapula River, Lake Bangweulu , Lake Bangweulu shoreline at rocky point near Samfya Ferry dock (11.35 ◦ S, 29.56 ◦ E) (station JPF 05-014A); coll. Bills, Chilala and Friel, 24 September 2005 (one sexually mature male, 56.3 mm SL) (CU DNA tissue 88). CU 91147; Luapula River, Luongo River at bridge on road from Kashiba to Mwenda (10.47 ◦ S, 29.02 ◦ E) (station JPF 05-023); coll. Bills, Chilala and Friel, 1 October 2005 (two specimens including one sexually mature male, 88.9 and 121.7 mm SL) (CU DNA tissue 177). CU 91148; Luapula River, Luongo River, Lufubu River Falls below bridge at Chipili on road from Mansa to Mununga (10.73 ◦ S, 29.09 ◦ E) (station JPF 05-025); coll. Bills, Chilala & Friel, 2 October 2005 (five specimens including two sexually mature males, 50.4–59.4 mm SL) (CU DNA tissue 187 and SAIAB DNA tissue 188). CU 91149; Luapula River, Luongo River, Luongo River at Mukonshi Bridge on road from Mwenda to Kawambwa (10.14 ◦ S, 29.16 ◦ E) (station JPF 05-030); coll. Bills, Chilala and Friel, 3 October 2005 (two sex undetermined specimens, 67.4 and 107.1 mm SL) (CU DNA tissue 233). CU 91150; Luapula River, Luongo River, Lubulafita Stream at bridge on road from Mwenda to Kawambwa (9.99 ◦ S, 29.11 ◦ E) (station JPF 05-031); coll. Bills, Chilala and Friel, 3 October 2005 (one sex undetermined specimen, 75.7 mm SL). CU 91151; Luapula River, Kalungwishi River, above Lumangwe Falls on Kalungwishi River (9.54 ◦ S, 29.39 ◦ E) (station JPF 05-039); coll. Bills, Chilala and Friel, 8 October 2005 (one sex undetermined specimen, 75.3 mm SL) (CU DNA tissue 310). CU 95316; (northern Zambia on label), Luapula River, Chambeshi River, Samfa Rapids at pontoon on Chambeshi River (10.85 ◦ S, 31.17 ◦ E) (station JPF 05-047); coll. Bills, Chilala and Friel, 11 October 2005 (eight sex undetermined specimens in total, five examined, 55.0– 77.2 mm SL) .

Figures

Figure 1. Map of Africa (top right) showing the location of the Congo basin. The first inset at centre details the topography of the Congo River and its main tributaries and rapids/falls sections. The second inset (bottom left) provides a detailed map of the Bangweulu-Mweru ecoregion (comprising the Luapula River basin), located in the southeastern-most part of the Congo River basin. The filled circle indicates the type locality of the new species Petrocephalus frieli sp. nov.; open circles indicate additional localities. The filled triangle indicates the type locality of Petrocephalus squalostoma; open circles indicate additional localities. Filled diamond marks the estimated location of the first specimen identified as Petrocephalus simus by Boulenger (1920) (identification uncertain, see text for details).

Figure 3. Photographs of Petrocephalus frieli sp. nov. and Petrocephalus squalostoma from the Bangweulu-Mweru ecoregion, Luapula River system, Congo basin. (A) Preserved holotype of P. frieli sp. nov. (CU 96866, scale bar 1.0 cm) (photograph by John P. Sullivan, CUMV). (B) Live specimen of P. frieli sp. nov. of about 8.0 cm [estimated] standard length (photograph by Roger Bills, SAIAB). (C) Live specimen of P. squalostoma of about 8.0 cm [estimated] standard length (photograph by Roger Bills, SAIAB).

Figure 4. Petrocephalus phylogenetic tree (20 species, 60 haplotypes, 77 specimens, not considering the outgroups) estimated by maximum likelihood using cytochrome b sequences (see text for details on the phylogenetic reconstruction method). Cytochrome b sequences of three mormyrins species – Gnathonemus petersii, Mormyrops nigricans and Myomyrus macrops – were used to root the tree. Species names followed by specimen numbers. Numbers at nodes are bootstrap proportions (if> 50%) and are only shown for interspecific relationships. The positions of Petrocephalus frieli sp. nov. and Petrocephalus squalostoma are highlighted with grey-filled boxes. Geographical origins of the examined specimens are indicated on the right. The scale bar corresponds to 0.04 substitutions per site.