Stomatorhinus ivindoensis, Sullivan, John P. & Hopkins, Carl D., 2005

Sullivan, John P. & Hopkins, Carl D., 2005, A new Stomatorhinus (Osteoglossomorpha: Mormyridae) from the Ivindo River, Gabon, West Central Africa, Zootaxa 847, pp. 1-23 : 3-12

Stomatorhinus ivindoensis new species

Figs. 1 & 2 .

Holotype. CU 85157 (original specimen no. 2161), male, 43.5 mm SL. Gabon, “Bialé Creek”: a small tributary of the Ivindo River inside the Ipassa Plateau Reserve near Makokou, (0° 32.3’ N, 12° 49.6’ E). Dip net, C.D. Hopkins, 2 September 1975.

Paratypes. Seventy­two specimens from three localities. The 10 paratypes selected for a complete set of measurements are indicated in Table 1.

Near village of Ébiègn on Rte. N.4, ca. 18 km E. of Makokou, Gabon (0° 35.5’ N, 12° 43.0’ E), 3 Oct 1979, R. Lewis: CU 85465 (32, without specimen nos.), 20.9–53.3 mm SL. AMNH 235053 (10, without specimen nos.), 34.2–49.8 mm SL. MNHN 2004­ 1750–1759 (10, without specimen nos.), 38.4–50.7 mm SL. MRAC 2004­32 ­P­1–10 (10, without specimen nos.), 29.8–48.1 mm SL.

Balé Creek below bridge, ca. 500 m from the IRET field station on Ipassa Plateau, ca. 7 km SE of Makokou, Gabon (0° 31.1’ N, 12° 48.0’ E): CU 75437 (2, specimen nos. 1003, 1004), 37.9, 40.8 mm SL, 27 Oct 93, C.D. Hopkins. CU 86244 (2, specimen nos. 2143, 2144), 39.3, 41.1 mm SL, 16 Jan 98, C.D. Hopkins et al. CU 86247 (3, specimen nos. 2002, 2010, 2012), 42.3–49.5 mm SL, 11 Jan 98, C.D. Hopkins et al.

Creek at Makatabongoy crossing road from Makokou­Okondja (R.15), Gabon (0° 08.15’ N, 13° 43.0’ E): CU 86245 (3, specimen nos. 2223, 2352, 2358), 45.2–48.3 mm SL, 3 Oct 79, C.D. Hopkins et al.

Additional (non­type) specimens.

Balé Creek, IRET field station on Ipassa Plateau, SE of Makokou, Gabon (0° 31’ N, 12° 48.0’ E): CU 85385 (3) 30.0– 44.8 mm SL, 29 Nov 1976, C.D. Hopkins. CU 85486 (1, specimen no. 2367) 43.0 mm SL, 28 Jul 1976, C.D. Hopkins. CU 85496 (1, specimen no. 85–230) 38.7 mm SL, 9 Dec 1985, J. Crawford. CU 83094 (1, specimen no. 4879) 39.8 mm SL, 26 Aug 2001, C.D. Hopkins & M.E. Arnegard. CU 75442 (1, specimen no. 1027) 36.8 mm SL, 29 Oct 1993, C.D. Hopkins & M.A. Friedman. CU 79703 (1, specimen no. 2074) 45.1 mm SL, 15 Jan 1998, C.D. Hopkins et al. CU 86243 (2, specimen nos. 2078, 2155) 33.6, 46.7 mm SL, 15 Jan 1998, C.D. Hopkins et al.

Nyamé Pendé Creek inside Ipassa Plateau Reserve (0° 30’ N, 12° 47’ E): CU 85152 (1, specimen no. 2101) 44.3 mm SL, 5 Aug 1975, C.D. Hopkins & R. Askins. CU 86246 (2, specimen nos. 2133, 2136) 38.0, 40.0 mm SL, 17 Jan 1998, C.D. Hopkins et al. CU 89030 (1) 43.0 mm SL, 20 Sep 2002, Hopkins et al.

Mindouba Creek on route to IRET station (0° 31.6’ N, 12° 48.2’ E): CU 89048 (1, specimen no. 5701) 41.9 mm SL, 18 Sep 2002, C.D. Hopkins et al.

Near mouth of Mié Creek into Ivindo River, across from Ipassa Reserve (0° 27.3’ N, 12° 48.5’E): CU 85123 (6), 21.3–49.6 mm SL, 20 Aug 1975, C.D. Hopkins & R. Askins. CU 85128 (10), 35.5–48.0 mm SL, 20 Aug 1975, C.D. Hopkins & R. Askins. CU 85156 (1, specimen no. 2150), 47.4 mm SL, 20 Aug 1975, C.D. Hopkins & R. Askins.

Near villages of Ébiègn and Èdzua Megne on route N.4 ca. 16 km E. of Makokou (approx. 0° 35.5’ N, 12° 43’E): CU 85131 (11), 29.5–55.7 mm SL, 9 Sep 1976, C.D. Hopkins. CU 85132 (17, specimen nos. between 3067 and 3093), 21.0– 44.7 mm SL, 1 Oct 1979, R. Lewis. CU 85151 (12, specimen nos. between 3114 and 3125), 36.5–47.1 mm SL, 1 Oct 1979, R. Lewis. CU 85153 (15, specimen nos. between 3095 and 3113), 27.1– 47.1 mm SL, 1 Oct 1979, R. Lewis. CU 85154 (19, specimen nos. between 3045 and 3066), 26.2–51.2 mm SL, 1 Oct 1979, R. Lewis. CU 85446 (71), 20.5–52.0 mm SL, 3 Oct 1979, R. Lewis. CU 85464 (16), 32.2–50.8 mm SL, 10 Oct 1979, R. Lewis. CU 85487 (1, specimen no. 5015) 38.9 mm SL, Sep 2002, C.D. Hopkins. CU 85124 (4) 30.0– 48.5 mm SL, 7 Nov 1979, R. Lewis. CU 85126 (4) 24.6–44.5 mm SL, 24 Oct 1979, R. Lewis. CU 85503 (16) 32.6–51.0 mm SL, 7 Nov 1979, R. Lewis. CU 85378 (19) 32.6–52.7 mm SL, 1 Dec 1979, R. Lewis. AMNH 231101 (21) 23.6–51.7mm SL, 6 Nov 1975, W. Harder. AMNH 231102 (51) 22.1–49.8 mm SL, 18 Nov 1975, W. Harder. AMNH 231173 (17) 23.2–51.33 mm SL, 3 Aug 1975, W. Harder.

Near village of Mbès on route N.4 ca. 18 km E. of Makokou (0° 34.8’ N, 12° 41’E): CU 85125 (6), 37.0– 45.7 mm SL, 12 Aug 1976, C.D. Hopkins. CU 85155 (1, specimen no. 2365), 52.0 mm SL, 12 Aug 1976, C.D. Hopkins. AMNH 231100 (30) 32.7–55.1 mm SL. 20 Sept. 1975, W. Harder. AMNH 231104 (1) 45.9 mm SL, 20 Nov 1975, W. Harder. AMNH 231105 (2) 44.5, 48.8 mm SL, 20 Nov 1975, W. Harder. AMNH 231106 (2) 41.3, 46.4 mm SL, 20 Nov 1975, W. Harder.

8 km downstream of IRET Ipassa Plateau Reserve station (0° 27.3’ N, 12° 48.8’ E): CU 85160 (9), 28.0– 40.1 mm SL, 3 Aug 1976, C.D. Hopkins.

23 km W of Makokou along “route Fang” (N.4) (0° 33.5’ N, 12° 37.7’ E): CU 85159 (2) 40.3, 43.5 mm SL, 1 Dec 1979, R. Lewis.

7 km W of Makokou along “route Fang” (N.4) (0° 34.3’ N, 12° 46.5’ E): CU 85158 (1, specimen no. 2366) 44.0 mm SL, 1 Dec 1976, C.D. Hopkins.

Along banks of Ivindo River near Makokou (0° 33’ N, 12° 51’E): CU 85127 (13) 27.2­ 46.3 mm SL, 1 Aug 1975, C.D. Hopkins & R. Askins. CU 85477 (3) 27.9–45.5 mm SL, 1 Dec 1976, C.D. Hopkins.

Weni Creek, Makokou (30° N, 12°50’E): CU 85130 (8) 28.0– 41.8 mm SL. 22 Sep 1976, C.D. Hopkins. CU 85129 (16) 26.7–47.6 mm SL. 1 Oct 1976. C.D. Hopkins. CU 85499 (1) 30.6 mm SL, 11 Oct 1976, C. D. Hopkins.

Creek crossing road from Makokou to Okondja (R.15), ca. 60 km SE of Makokou (0° 18’ N, 13° 13’E): CU 85420 (1, specimen no. 5014), 40.2 mm SL, C.D. Hopkins & R. Lewis.

Near Makokou, Gabon; precise locality not specified: AMNH 231103 (1) 42.8 mm SL, 20 Nov 1975, W. Harder. AMNH 231151 (2) 30.0, 49.2 mm SL, 1978, W. Harder. AMNH 231166 (1) 25.5 mm SL, 29 July 1975, W. Harder. AMNH 231215 (1) 50.4 mm SL, no date, W. Harder.

Character Holotype N min max mean Std. Dev. Standard length, mm 43.75 11 37.37 53.09 44.37 4.75 Head length, mm 14.26 11 12.50 16.01 14.26 1.01 Percent of standard length

Maximum body depth 27.04 11 23.92 26.67 25.87 1.49 Head length 32.41 11 30.16 33.87 32.26 1.28 Snout length 7.77 11 7.77 8.40 8.10 0.19 Pre­dorsal distance 65.62 11 65.62 70.60 67.92 1.56 Pre­anal distance 59.98 11 59.98 67.73 63.27 2.24 Pre­pelvic distance 45.97 11 45.36 49.75 47.31 1.19 Pre­pectoral distance 30.83 11 30.57 33.36 31.68 0.87 Caudal peduncle depth 6.33 11 5.31 6.49 6.03 0.46 Caudal peduncle length 14.24 11 14.17 16.46 14.92 0.82 Head width 14.67 11 13.96 16.43 15.13 0.76 Pectoral fin length 18.81 11 15.96 19.81 18.42 0.99 Pelvic fin length 10.03 11 9.57 10.79 10.28 0.44 Pelvic­anal fin distance 15.22 11 15.22 21.66 17.79 2.31 Anal fin base length 25.44 11 22.83 25.44 24.05 0.85 Dorsal fin base length 21.10 11 18.15 21.10 19.89 0.86 Percent of head length

Snout length 23.98 11 23.68 27.57 25.15 1.22 Post­orbital length 69.25 11 66.91 71.83 69.41 1.52 Head width 45.28 11 42.52 50.59 46.96 2.47 Head depth 68.34 11 58.35 68.92 64.47 3.39 Eye diameter 9.87 11 6.65 10.10 8.30 1.19 Inter­nostril distance 24.82 11 23.04 26.70 24.96 1.11 Ratios

Inter­orbital width as % head width 84.42 11 71.92 90.41 76.72 5.77 Pre­anal distance/pre­dorsal distance 0.91 11 0.89 1.03 0.93 0.04 Caudal peduncle depth as % CP length 44.46 11 37.29 45.33 40.55 3.42 Length of dorsal/length of anal 0.83 11 0.80 0.88 0.83 0.02 Counts median quartile

range Dorsal rays 17 11 14 17 16 1.50 Anal rays 21 11 19 21 20 1.00 Anal rays before dorsal 5 11 5 5 5 0 Pectoral rays 8 11 8 9 9 1.00 Pelvic rays 6 11 6 6 6 0 Caudal peduncular scales 12 11 12 12 12 0 Teeth, upper jaw 7 11 7 8 7 1.00 Teeth, lower jaw 8 11 8 9 8 1.00 Total vertebrae 36 11 36 36 36 1.00 Scale rows from pelvic fin origin to lateral line 13 11 11 13 11 1.00 Lateral line scales with tube & exposed pore 24 11 22 34 26 2.50 Scales along longitudinal line 46 11 44 50 46 3.50 Diagnosis: Stomatorhinus ivindoensis is recognized by the combination of the following characteristics: (1) very small adult size (specimens larger than 56 mm SL never observed) with most adults between 35 and 48 mm SL; (2) caudal peduncle of moderate width (caudal peduncle depth 37–45% of caudal penduncle length); (3) a small eye, 6.7– 10% of HL; (4) 8 to 9 pectoral rays and 14 to 17 dorsal fin rays; (5) first 22 to 28 scales along lateral line bearing pores, last pore­bearing scale lying posterior to a vertical through origin of anal fin, but positioned well in advance of caudal peduncle; (6) lobes of the caudal fin broad and rounded, without distinct points at apices.

Description: A very small Stomatorhinus not known to surpass 56 mm SL. Morphometric ratios and meristics presented in Table 1. Body depth and width as proportions of SL are in middle range for species of this genus. In all but gravid females, depth at origin of anal fin equal to or slightly less than depth at mid­body. Greatest width at opercles. Dorsal and ventral profiles gently convex. The head profile is slightly convex above the eye, the snout is rounded to somewhat truncate and projects slightly beyond the mouth. Mouth small. No submental swelling. Eye small, covered by epidermis. Inter­orbital distance is 72–90% of head width. Nostrils well separated with posterior nostril located near rictus of mouth. Teeth 7–8/8–9, usually 7/8, bicuspid. Head (including eye), upper back and belly covered by epidermis that is translucent in life, semi­opaque in preservation. When pressed to side, tip of pectoral fin extends well past origin of pelvic fin. Pectoral fin has 8 or 9 rays. Dorsal and anal fins roughly symmetrical above and below body axis, the anal fin (of 19–21 rays) slightly longer, with the dorsal fin (of 14–17 rays) originating at vertical through the origin of the fourth or fifth anal fin ray; the origins of the last dorsal and last anal fin rays at roughly the same vertical. Lobes of caudal fin short, very rounded and blunt. Caudal peduncle relatively short (14–16.5% of SL), of moderate depth (37–45% of length), with 12 circumpeduncular scales. First 22–28 scales along lateral line bearing pores, last pore­bearing scale lying past vertical through origin of anal fin. Total scales along longitudinal line 44–50. Scale rows between origin of pelvic fin and lateral line scale 11 to 13. Total vertebrae 36 (excluding urostyle).

Color: In life, specimens are uniformly dark chocolate brown, with little patterning in pigment along the body. Fins are translucent with dark brown pigmented rays. In alcohol, thick epidermis overlying head (including eye), upper back and belly appears opaque.

Size and sexual maturity: Review of 504 specimens in 54 lots from several localities reveals no specimens larger than 56 mm SL. Mature males are identifiable by a pronounced anal fin notch from about 35 mm SL. Gravid females are often enormously distended with eggs (e.g. female paratype shown in Fig 2 D).

Distribution and ecology: All known collections of S. ivindoensis come from the upper Ivindo River ( Fig. 3 ). Most were made in the vicinity of Makokou and the nearby field station located inside the Ipassa Plateau Reserve on the right bank of the Ivindo River. The species is usually taken along the margin of small forest streams ( Fig. 4 ) in root tangle where it occurs with other species of mormyrids, but has also been taken along the margin of the Ivindo River proper in deep water. Individuals are often found spaced apart at intervals of 50 cm to one meter. Diet of this species has not been studied, but is probably similar to that reported for S. polli Matthes 1964 in which stomach contents were dominated by small crustaceans and insect larvae.

Electric organ discharge: Stomatorhinus ivindoensis has a 110 to 720 microsecond duration EOD waveform with three to four peaks in the discharge ( Fig. 5 A–F). The EOD begins with a small head­negative phase or peak, P0, followed by a larger head­positive phase, P1, followed by the largest head­negative peak, P2. In some fish, the discharge ends with a final head­positive phase, P3. The peak spectral frequency of the Fourier Transform of the EOD is between 4000 Hz and 16,000 Hz. Average peak heights, total durations, and spectral peak frequencies for this species, are listed in Table 2. The EOD is sexually dimorphic among sexually mature individuals. Juvenile male EODs are similar to female EODs. Male EODs are longer in duration and have lower FFT peaks than females. They also differ in the heights of peaks P0 and P1 relative to the full peak to peak height compared to females ( Table 2). The EOD of a juvenile of this species was reported by Heymer & Harder (1975).

Etymology: Named for the Ivindo River of Gabon.

n mean S.D. mean S.D. mean S.D. mean S.D. mean S.D. mean S.D. P0 P1 P2 P3 FFT EOD height height height height peak duration

% % % % (Hz) (µs)

S. ivindoensis

Female 17 ­4.9 1 3.8 23.9 2 7.1 ­67.6 4.3 13.1 2 8.7 13017 1 2562 185 1 62

Male 12 ­12.0 1 7.0 31.8 2 7.0 ­66.7 4.9 28.5 2 8.5 7593 1 3661 374 1 172

S. walkeri

Female 8 ­2.5 1 2.2 26.3 6.4 ­69.2 6.7 19.5 10.3 18268 1 6069 138 1 63

Male 6 ­0.6 1 1.0 24.7 5.0 ­73.8 6.0 24.4 10.5 16699 1 7455 140 1 84

1 Male S. ivindoensis differ from all three other groups using Scheffe’s post­hoc test, p <0.01. 2 Male S. ivindoensis differ from female S. ivindoensis . Scheffe’s post­hoc test, p <0.05

Figures

FIGURE 1. Drawing of Stomatorhinus ivindoensis n. sp. holotype, 43.8 mm SL. Drawn by Vera Ming Wong.

FIGURE 2. Photograph (A) and radiograph (B) of preserved holotype of Stomatorhinus ivindoensis n. sp., CU 85157, 43.8 mm SL, male; (C) live paratype specimen no. 1004, CU 75437, 40.8 mm SL, male; (D) preserved paratype, CU 85465, 52.2 mm SL, female.

FIGURE 3. Collection sites of Stomatorhinus ivindoensis n. sp. (circles) and S. walkeri (triangles) in the Ivindo and Ogooué River basins of Gabon and the Kouilou­Niari basin of the Republic of Congo. Shaded areas delimit the boundary of the Lower Guinea ichthyofaunal province of West Central Africa.

FIGURE 4. Typical forest creek habitat of Stomatorhinus ivindoensis n. sp.: upper “ Balé Creek ” within the Ipassa Plateau Reserve near Makokou, Gabon.

FIGURE 5. EOD waveforms (left) and power spectra (right) for Stomatorhinus ivindoensis n. sp. The holotype of S. ivindoensis, a male, is shown in A and B. Peaks are numbered in order from P 0 to P 3. EOD waveforms are centered about the largest head­negative peak and plotted with head positivity upward. Power spectra are normalized so that the peak energy is adjusted to 0 dB. EODs of reproductive males (E, F) are longer in duration and have a lower peak power frequency than those of females (C, D). Individual specimen numbers are indicated beneath waveforms; F = female, M = male, H = holotype. Time base = 0.1 millisecond.