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Dorsal spines (total): 0-0; Dorsal soft rays (total): 19-21; Anal spines: 0-0; Anal soft rays: 24-26; Vertebrae: 41-44. Diagnosis: Paramormyrops ntotom is distinguished from all other Lower-Guinea Paramormyrops by a combination of morphological and electrical characteristics: 5 teeth in upper-jaw, 6 in lower; 12 circumpeduncular scales; V-shaped snout profile viewed from above, snout angle 38-50°, corresponding to an interorbital width 0.8-1.05 times the snout length; body depth 14.9-18.1% of standard length, 81-91.6% of body depth at urogenital pore; eye diameter 12.4-14.7% of head length measured to end of opercular bone; snout length 23.8-28.3% of head length; ratio of head length to depth 1.25-1.40; head length 20.4-24.6% of standard length; EOD waveform with two phases, head positive then negative, duration 4.78 ± 1.10 ms with a corresponding peak power spectral frequency, 265 ± 67 Hz; electric organ composed of type NPp electrocytes (Ref. 116799). With its 5/6 teeth, 12 circumpeduncular scales and sharp snout, Paramormyrops ntotom differs from all other described Paramormyrops except P. curvifrons and P. spekodes (Ref. 116799). Five morphological characters distinguish P. ntotom from P. curvifrons: ratio of head length to standard length shorter in P. ntotom compared with P. curvifrons; slight concave depression in the forehead in advance of the orbit and a relatively compact snout compared to P. curvifrons which has a longer snout, downward sloping, often with a slightly protruding chin and upper lip; shorter prepectoral distance relative to predorsal distance; snout angle greater in P. ntotom than P. curvifrons; and the head depth relative to head length greater in P. ntotom than in P. curvifrons; EOD duration slightly longer in P. ntotom compared with P. curvifrons, with extensive overlap; both species have type NPp electrocytes in the electric organ and both exhibit sex differences in EOD duration (Ref. 116799). Paramormyrops ntotom differs from P. sphekodes in the six following morphological characters: larger overall size at sexual maturity; head more elongate and less rounded; snout reduced; larger caudal peduncle depth to length ratio; the smaller eye diameter relative to head length; and the greater EOD duration; when alive P. ntotom is most easily distinguished from P. sphekodes by its longer EOD duration and a correspondingly lower peak spectral frequency; the EODs of P. ntotom and P. sphekodes also differ in shape, with the width of first and second phase being equal for P. ntotom, while W1 is longer than W2 in P. sphekodes; living specimens of these two species also differ in colouration: dorsal and anal fin pigmentation tends to be darker in P. ntotom than P. sphekodes, and the ground colour of the skin tends to be darker chocolate brown compared to yellow brown in P. sphekodes (Ref. 116799).
Description: A large-bodied Paramormyrops; body laterally compressed with maximum width at opercular bones, 8.43-10.42% of standard length; viewed laterally, body depth increases gradually from base of the pectoral fin to its maximum at origin of the anal fin; body depth at pectoral fin, 14.9-18.1% of standard length, body depth at urogenital pore 16.7-21.5% of standard length; the ratio of these two depths, 0.819-0.916, reflects the slight increase posteriorly compared to P. sphekodes; body depth decreases from origin of dorsal and anal fins to caudal peduncle; caudal peduncle length 15.8-19.4% of standard length, slightly deeper at origin than centre, caudal peduncle depth 26.1-33.7% of caudal peduncle length; lobes of caudal fin rounded (Ref. 116799). Lateral head profile straight and downward sloping from a point half way between opercular opening and tip of the snout, slightly concave above the eye in some specimens; head and snout V-shaped when viewed dorsally, snout angle, 38-50° intermediate between that of P. curvifrons and P. sphekodes; head length 19.6-24.6% of standard length, similar to P. sphekodes, but shorter than P. curvifrons; head depth measured from external landmarks 64.8-79.8% of head length, or 1.13-1.35; when measured from radiographs 1.25-1.38; in lateral view, snout tip lies along mid-horizontal line (Ref. 116799). Teeth bicuspid, 4-5 in upper and 6 in lower jaws (Ref. 116799). Mouth small, rictus directly beneath nares; chin slightly swollen below gular region, not extending beyond snout; eye small, eye diameter 10.6-15.0% of head length; eye socket forms light ring around dark eyeball, with gold iris and dark centre; interorbital width 22.4-31.4% of head length; anterior naris at about 1/3 distance from snout tip to eye, slightly below line drawn through centre of eye, posterior naris halfway between anterior naris and eye, level with lower margin of eye; opercular opening begins anterior to base of pectoral fin; postorbital length 62.8-68.1% of head length (Ref. 116779). Pectoral-fin origin beneath posterior terminus of opercular opening, slightly below mid-horizontal line, pectoral length 14.6-16.8% of standard length, 10-12 rays; pelvic-fin origin at 34.6-38.8% of standard length, length 8.2-11.1% of standard length, positioned ventrally, 6 rays; pre-dorsal distance 61.4-66.1% of standard length; anterior margin of dorsal fin gently convex, trailing margin concave in first third, remainder levels off at 1/2 dorsal-fin height; maximum dorsal-fin height 59.0-83.2% of dorsal-fin length, 19-21 total rays; anal-fin origin slightly anterior to dorsal-fin origin; dorsal-fin origin above seventh anal ray, or fifth branched ray; anal fin mirrors general shape of dorsal fin, maximum height 50.4-71.8% of anal fin length; in males, anterior anal fin ray thickened and stiff, noticeable notch in body spanning anterior half of anal-fin base; anal-fin base terminus directly beneath that of dorsal fin, rays 24-26; lobes of caudal fin rounded, equal, slightly wider than caudal peduncle, deeply cleft, scaled at the bases (Ref. 116799). Scales fin, cycloid, absent from head; pierced lateral line scales 57-72, 9-12 scale rows between anterior base of dorsal fin and lateral line, 10-14 scale rows from pelvic fin to lateral line; circumpeduncular scales 12 (Ref. 116799). Vertebrae: 41-44 total, 18 pre-caudal and 22-26 caudal (Ref. 116799).
Colouration: All fins with lightly to heavily pigmented rays, membranes hyaline; no dark band bases of dorsal and anal fins; body darker dorsally, lighter ventrally (Ref. 116799). When alive, tan to light chocolate brown body with olive accents on top of head, back and belly; mouth, chin and sometimes gular region unpigmented, white to grey; many small white pores visible on top of head and back, with fewer, large white pores (Knollenorgans) on head (Ref. 116799). Preserved specimens are uniform greyish-brown (Ref. 116799). |
