Pollimyrus vanneeri, Dierickx & Lunkayilakio & Bills & Vreven, 2025

Dierickx, Katrien, Lunkayilakio, Soleil Wamuini, Bills, Roger & Vreven, Emmanuel, 2025, Morphometric synthesis of Pollimyrus (Teleostei, Mormyridae) with the description of four new species, Journal of Fish Biology 106 (3), pp. 846-892 : 860-864

3.2.3 | Pollimyrus sp. “ kouilou-niari ” group

The specimens originating from the Kouilou-Niari River, a coastal river basin of the Lower Guinea ichthyogeographical province (IP) in the Republic of the Congo, is here preliminarily identified as Pollimyrus sp. “ kouilou-niari.” It can be distinguished from all other Pollimyrus species by having a thick caudal peduncle compared to the slender caudal peduncle of all Pollimyrus species (20.3%–24.2% BD vs. 12.7%–20.2% BD), a blocky snout (vs. usually round), and no mental lobe (vs. small mental lobe) compared to thick-tailed Pollimyrus , and rounded pectoral fin (vs. pointed) compared to the members of the P. isidori group.

Only one other congeneric species occurs in the same IP, P. guttatus , which occurs near Kribi, in the Kineke River in southern Cameroon. The specimens from the Kouilou-Niari River can be distinguished from P. guttatus by having a subterminal mouth (vs. terminal mouth), a shallower body depth (22.6%–28.7% SL vs. 30.7%–32.1% SL), a shorter pre-ventral distance (33.7%–40.2% SL vs. 43.7%–45.7% SL), more dorsal-fin rays (21–24 vs. 18–19), more vertebrae (41–43 vs. 37–38), and more lateral-line scales (59–73 vs. 43–52).

As these specimens are morphologically distinct from all other Pollimyrus , they are here identified as a new species to science: Pollimyrus vanneeri sp. nov. (Figure 11). The detailed description of this species new to science is provided later.

3.2.4 | Slender-tailed group

A PCA on 26 log-transformed measurements shows a slight separation of C. plagiostoma , P. pedunculatus , and P. sp. “ luki ” on a combination of PC 2, with the most important loadings being the caudal peduncle length, length of the dorsal fin, the posterodorsal distance, and PC 3, with the most important loadings being the snout length, the length of the dorsal fin, and the eye diameter (Figure 6b; Table S4 for the loadings; also see Figure S22). A PCA on the meristics shows a separation of C. plagiostoma on PC 1, with the most important loadings being the number of dorsal-fin rays, pectoral-fin rays, and scales between the anal-fin origin and lateral line, P. pulverulentus , P. nigripinnis , P. maculipinnis , P. osborni , and P. schreyeni on PC 2, with the most important loadings being the number of teeth in the upper jaw, teeth in the lower jaw, and vertebrae, and P. maculipinnis , P. osborni , and P. schreyeni on PC 3, with the most important loadings being the number of anal-fin rays, caudal peduncle scales, and the scales between the lateral line and dorsal-fin origin (Figure 6d; Table S5 for the loadings).

Cyphomyrus plagiostoma (Boulenger, 1898) (Figure S4) differs from all the other slender-tailed Pollimyrus by having more dorsal-fin rays (32–33 vs. 14–28) and a dorsal fin that is longer than the anal fin (130.0%–136.4% LD vs. 42.9%–111.1% LD). These characteristics also differentiate this species from all other Pollimyrus species.

Pollimyrus schreyeni Poll, 1972 (Figure S13) has fewer scales between the pelvic fin origin and the lateral line compared to the other slender-tailed Pollimyrus (9–11 [median 10] vs. 11–18 [median 14]). It differs by the number of dorsal-fin rays from P. pedunculatus (17 vs. 19), from P. adspersus (17 vs. 19–20), from P. pulverulentus (17 vs. 22–24), and P. nigripinnis (17 vs. 18–23). It has a dorsal fin that originates clearly posteriorly to the level of the anal-fin origin, whereas in all other Pollimyrus species, it originates slightly anteriorly, slightly posteriorly, or at the same level as the anal fin. Its dorsal fin is slightly shorter than half the anal fin, whereas in all other species it is longer than half this length or even slightly longer than the entire length of the anal fin (42.9%–46.8% LA vs. 63.1%–136.98% LA). The anal fin is slightly longer than one third of the standard length in P. schreyeni (34.7%–35.4% SL vs. 19.9%–32.1% SL in other Pollimyrus ). It has more fin rays (30–32 vs. 20–28) than all other Pollimyrus species. Further, compared to all other Pollimyrus species, the four type specimens included in the study have a distinct colouration after preservation. These fish are generally light brown with large-sized, dark brown spots, covering several scales, whereas most other Pollimyrus species are plainly colored, with sometimes a vague midlateral line or small-sized spots, which are smaller than a scale (see Figure S16).

Pollimyrus pedunculatus ( David & Poll, 1937) (Figure S14), only known from the holotype, is the only slender-tailed Pollimyrus species in which the anterior nostril is positioned lower than the posterior one. Further, it has a long and slim caudal peduncle compared to the other slender-tailed Pollimyrus species (CPD%CPL; 20.6% CPL vs. 24.4%–37.6% CPL), except for C. plagiostoma , which also has a rather slender tail (19.3%–25.6% CPL). The pre-pelvic distance is shorter compared to that of all other Pollimyrus (34.3% SL vs. 36.0%– 42.9% SL). Its pelvic fin seems shorter than in all other Pollimyrus species (7.0% SL vs. 8.4%–13.4% SL). However, it cannot be ruled out that this is caused by some damage, as the distal tip of the holotype's fin seems slightly tapered.

Pollimyrus maculipinnis (Nichols and LaMonte, 1934) (Figure S15) has a holo- and a paratype that are small (52.9–53.9 mm SL). This species clearly differs from the other slender-tailed Pollimyrus species by several measurements and meristics. It differs from P. nigripinnis and P. pulverulentus by having a thicker caudal peduncle (5.6%–6.4% SL vs. 3.9%–5.3% SL and 4.1%–4.7% SL) and fewer teeth in the upper jaw (7 vs. 8–10 and 9–10). It differs from P. adspersus , P. sp. “ luki,” P. osborni , and P. pedunculatus by having a longer head (25.3%–25.3 SL vs. 21.5%–23.7% SL). P. maculipinnis has fewer dorsal-fin rays compared to the specimens identified as P. nigripinnis , P. adspersus , and P. pedunculatus (17–17 vs. 19–23), and fewer anal fin rays than P. pulverulentus and P. schreyeni (24–24 vs. 27–32).

Pollimyrus nigripinnis ( Boulenger, 1899) (Figure S16) and P. pulverulentus ( Boulenger, 1899) (Figure S16) are hard to distinguish from each other. Based on the collected morphometric data, the type specimens of P. nigripinnis and P. pulverulentus overlap in measurements and meristics (also see Table 5). A PCA on 26 log-transformed measurements shows a clear separation of the two nominal species on PC 2, with the most important loadings being the snout length, belly length, and the caudal peduncle length. The same is true for a PCA on the meristics on PC 2, with the most important loadings being the number of vertebrae, caudal peduncle scales, and lateral-line scales (Figure 7; also see Tables S7 and S8 for the loadings). However, they cannot be distinguished visually on any qualitative or quantitative characteristic, and the ranges for the measurements and meristics do not allow for a clear separation due to overlap. With the type localities of both nominal species being in the Middle Congo basin (Figure 2), they might belong to one and the same species. Therefore, both species are regarded as synonyms and from now on referred to

Pollimyrus pulverulentus Pollimyrus nigripinnis P. nigripinnis “Uéré ” P. nigripinnis “lac Measurement syntype (n = 4) syntype (n = 6) syntype (n = 1) bleu” (n = 5)

Characteristic (in % SL)

BD 30.0–33.4 28.4–30.7

BL 18.1–23.6 22.2–24.7

PPL 29.2–30.1 26.6–28.7 LD a 22.8–25.4 20.9–23.6

LA 28.6–30.8 27.1–28.7

LV 11.3–12.3 9.9–11.1 CPL 14.0–16.3 16.4–18.1 HL a 24.9–26.8 23.5–25.3

Characteristic (in % BD) CPD a 13.7–14.4 15.3–16.9

Characteristic (in % HL) SnL 16.4–16.7 9.8–17.4

HW 47.7–54.7 47.5–51.3

Na 7.7–8.3 6.8–8.2 OD a 22.2–24.5 22.8–24.2 IOW a 29.8–38.0 31.1–35.7

UJW 16.2–19.5 15.0–17.8 LJW a 15.6–17.9 15.9–18.6

Meristic

Dorsal-fin rays a 22–24 19–21 Anal-fin rays 27–28 25 Vertebrae a 38 38–40 Upper-jaw teeth a 9–10 8–9

Lateral-line scales 49–54 47–54

Caudal peduncle 11–14 12–16 scales

28.2 30.7–35.7

21.6 19.0–22.4

29.8 27.9–30.2

18.5 22.3–24.8

28.1 28.0–29.8

11.8 10.8–12.4

16.5 13.6–17.3

27.1 25.0–27.7

18.3 12.7–17.4

15.4 18.2–20.0

49.3 47.6–54.1

7.8 8.5–9.1

25.3 17.5–24.9

38.7 31.1–39.1

17.2 15.5–21.5

18.8 14.2–20.8

18 19–23

25 25–27

37 37–39

10 9–10

47 42–52

13 11–12

Note: See Table 3 and Figure 1 for definitions of the abbreviations. The full list of morphometric characteristics can be found in Table S9.

a Indicates the measurements and meristics where the syntype series of P. nigripinnis ( Boulenger, 1899) differ.

as P. pulverulentus ( Boulenger, 1899) (see Discussion for more details). Non-type specimens identified to the P. pulverulentus complex found in Lac Bleu appear to resemble the types of P. pulverulentus most morphologically, as seen in the observed ranges for the different nominal species (Table 5) and in PCAs on the measurements and meristics (Figure 7).

Pollimyrus pulverulentus differs from P. adspersus , P. osborni , P. pedunculatus , and P. sp. “ luki ” by having a longer pre-pectoral distance (26.6%–30.2% SL vs. 20.1%–25.9% SL). It also differs in dentition, having 8–10 teeth in the upper jaw and 9–11 teeth in the lower jaw, from P. osborni (7 teeth in the upper jaw) and P. adspersus (8 teeth in the lower jaw). Their teeth have small cusps that are not as obvious as those of P. adspersus , P. fasciaticeps , P. maculipinnis , P. osborni , and Pollimyrus sp. “ luki ”.

One of the syntypes of P. nigripinnis shows some morphological differences from the other syntypes. Six syntypes were collected from Kutu at Lake Mai-Ndombe, and one was collected from the Uéré River (RMCA P.344: 61.3 mm SL) (Figure 2; also see Supplementary file S1 for hydro-geographic locations). The latter has a deeper caudal peduncle relative to its body depth (18.3% CPL vs. 15.3%–16.9% CPL), a longer head (27.1% SL vs. 23.5%–25.3% SL), a shorter dorsal fin (18.5% SL vs. 20.9%–23.6% SL), a wider lower jaw (18.8 vs. 15.9%–18.6% HL), and a wider interorbital distance (38.7% HL vs. 31.1%–35.7% HL) compared to the other syntypes of P. nigripinnis from Kutu. Its mouth is positioned subterminally, whereas in the Kutu syntypes, it is positioned terminally. Further, it also has fewer dorsal-fin rays (18 vs. 19–21) and vertebrae (37 vs. 38–40), but more upper-jaw teeth (10 vs. 8–9) (Table 5). Finally, it is also clearly separated on a PCA of the 26 log-transformed measurements on PC 3, with the most important loadings being the lower-jaw width, dorsal-fin length, and eye diameter (Figure 7). This specimen is, however, not as well preserved as the other syntypes. Even though it is possible that this specimen is simply badly preserved, some characteristics indicate that the syntype series of P. nigripinnis is polyspecific. This idea is further supported by the wide hydro-geographical separation of Kutu and Uéré. Thus, syntype RMCA P.344 is further referred to as P. nigripinnis “Uéré ,” given the clear differences in morphology from the other syntypes. Although P. osborni has been described from the Uele River, of which the Uéré River is an affluent, P. nigripinnis “Uéré ” clearly differs from the holotype of P. osborni by its lower number of circumpeduncular scales (13 vs. 17 in P. osborni ) and in, for example, head width (49.3% HL vs. 57.5% HL in P. osborni ) (also see Tables 6 and 7). Thus, both these two specimens are clearly not conspecific despite occurring in the same (sub)basin. It is currently unclear if P. nigripinnis “Uéré ” could represent a species new to science due to the lack of similar specimens from the same locality or (sub)basin.

Pollimyrus osborni (Nichols and Griscom, 1917) (Figure S17) is only known from the holotype. The species differs from most slender-tailed species by the aforementioned characteristics for each of the species already differentiated in the complex. Further, it can be distinguished from P. adspersus by having a wider head length (57.5% HL vs. 51.1%–51.9% HL), a longer pre-ventral distance (42.2% SL vs. 36.0%–36.7% SL), and fewer dorsal- (17 vs. 19–20) and anal-fin rays (24 vs. 27). Finally, it differs from P. sp. “luki” by having more circumpeduncular scales (17 vs. 12–15) and relatively long and broad teeth that are packed closely together (vs. teeth that are smaller and have an open space between them).

Specimens found in the Luki River in the Democratic Republic of the Congo, here preliminarily identified as Pollimyrus sp. “ luki,” differ from all previously mentioned slender-tailed species as described earlier. They have overlapping ranges of all measurements with P. adspersus (Table 6). No differences in meristics could be found (Table 7). Nevertheless, the teeth of these specimens are small, whereas the teeth of P. adspersus are larger and take in more space in the upper jaw. In the lower jaw, the teeth of these specimens are more embedded and have mostly symmetrical cusps, whereas the teeth of P. adspersus are asymmetrical, with one cusp being larger than the other. In the upper jaw, all specimens found in the Luki River have a type 1 dentition (Figure 1e), whereas the type specimens of P. adspersus have either a type 2 or have an additional tooth behind the most anterior tooth. As such, the specimens found in the Luki River can be regarded as separate species based on their well-distinct dentition. Furthermore, the species probably differ in their known geographic occurrence, with the syntypes of P. adspersus having been reported from “West Africa” ( Günther, 1866). As these specimens are morphologically distinct from all other Pollimyrus , they are proposed as a new species to science: Pollimyrus ibalazambai sp. nov. (Figure 15). The detailed description of this species new to science is provided below.

Pollimyrus adspersus ( Günther, 1866) (Figure S18) differs from all other slender-tailed Pollimyrus as mentioned earlier.