Roberts and Stewart 1976
CountryLower Congo River: freshwater
Holotype: MCZ 50236.
Paratypes: MCZ 50294, BMNH 19126.96.36.199–25, MRAC 76-17-P-5–6, MCZ 50237, MCZ 76321, MCZ 50379.
There are nine species in the genus Notoglanidium Günther 1903: Notoglanidium akiri (Risch 1987), Notoglanidium boutchangai (Thys van den Audenaerde 1965), Notoglanidium depierrei (Daget 1980), Notoglanidium macrostoma (Pellegrin 1909),Notoglanidium maculatum (Boulenger 1916), Notoglanidium pallidum Roberts and Stewart 1976, Notoglanidium pembetadi Vreven, Ibala Zamba, Mamonekene and Geerinckx 2013, Notoglanidium thomasi Boulenger 1916, Notoglanidium walkeri Günther 1903. Geerinckx et al. (2013) have two trees based on 24 morphological and osteological characters. They do not agree on the placment of N. pallidum. Their tree 1 has N. macrostoma as sister to the other eight species with N. pallidum sister to the other seven. Their tree 2 had N. pallidum and N. walkeri as sisters with N. macrostoma as sister to these two.
Roberts and Stewart (1976) say of N. boutchangai: "[Notoglanidium] boutchangai Thys 1965, [is] a microphthalmic, dorsally flattened fish of uniformly dark brownish coloration and a relatively high dorsal fin with seven branched rays, known only from the rapids of the riviere N gounie (Ogowe basin) near Lebamba, Gabon". (Emphasis added). It thus seems to be somewhat similar ecologically to N. pallidum.
This is the description of Notoglanidium pallidum from the revisionary study of Geerinckx et al. (2013):
Notoglanidium pallidum Roberts & Stewart 1976
(Figs. 4C, 4D & 10F)
Holotype. MCZ 50236: Congo River near Bulu, west of Luozi, Democratic Republic of the Congo (Congo-Kinshasa); 5° 01’ S, 14° 01’ E; 53 mm SL (only images of specimen examined).
Paratypes. MCZ 50294: Congo River at Tadi, near Kibunzi, Democratic Republic of the Congo (Congo-Kinshasa); 5° 14’ S, 13° 56’ E; 5 out of 16 spec. examined, 19–83 mm SL. BMNH 19188.8.131.52–25: same locality; 2 spec., 40–63 mm SL. MRAC 76-17-P-5–6: same locality; 2 spec., 36–76 mm SL. MCZ 50237: same locality as holotype; 20 mm SL (not examined). MCZ 76321: same locality; two out of four cleared and stained spec. examined, 41–58 mm SL. MCZ 50379: Zaire River main stream a few km northeast of Kinganga; 73 mm SL (not examined).
Diagnosis. Notoglanidium pallidum differs from other species in the genus in having: a small eye diameter (3.8–7.0% HL) [vs. larger in N. boutchangai (7.5–10.4% HL), N. walkeri (7.8–10.6% HL), N. thomasi (9.1–12 5% HL) and N. macrostoma (9.1–13.3% HL)]; a small interorbital distance (20.0–23.3% HL) [vs. larger in N. akiri (24.1–32.8% HL), N. macrostoma (28.0–40.4% HL), N. maculatum (35.3–36.8% HL), N. thomasi (41.0–46.7% HL) and N. walkeri (27.8–33.3% HL)]; a small combined premaxillary tooth plate width (11.1–15.3% HL) [vs. larger (>18.2% HL) in N. akiri, N. boutchangai, N. depierrei, N. macrostoma and N. pembetadi]; an average number of soft dorsal-fin rays (8–10) [vs. seven rays in N. akiri, N. boutchangai and N. macrostoma, and >10 rays in N. maculatum (16–22), N. thomasi (12–16) and N. walkeri (11–15)]. Description. Both head and body dorsoventrally flattened, with depth almost constant from head to body (predorsal body depth 10.6–14.3% SL, minimal caudal peduncle depth 9.1–10.4% SL, head depth 9.8–13.8% SL). Branchiostegal membranes fused along anterior half only, with a slit separating the posterior halves (they may overlap). Adipose fin low (2.3–3.3% SL). See also Table 4.
Colouration in life. Pallid pink, without any markings (pale brownish when preserved).
Maximum size recorded. 81 mm SL.
Etymology. The species name indicates the pale (pallidus, Latin) skin of the species.
Distribution. Congo River west of Luozi, and more downriver at Tadi (Kibunzi; Fig. 13).
The lower Congo River, and especially the northern and southern rapids below Pool Malebo, are home to many endemic species (Roberts and Stewart 1976, Bailey 1986, Thieme et al. 2005, Mamonekene 2005, Alter et al. 2015, Alter et al. 2017, Stiassny 2016). In particular there are at least eleven species, in five Families, which exhibit the troglomorphic features of reduced eyes and pigment:
Notoglanidium pallidum Roberts and Stewart 1976
These features probably evolved because these species live at depth within the rapids and spend their whole lives in permanent darkness, analagous to life in caves. The ocular and craniofacial anatomy of several of these species have been studied (Schobert et al. 2010, 2011, 2013) but almost nothing else is known about these animals.
Moelants, T. 2010. Notoglanidium pallidum. The IUCN Red List of Threatened Species 2010: e.T182359A7868521. https://dx.doi.org/10.2305/IUCN.UK.2010-3.RLTS.T182359A7868521.en. Downloaded on 20 March 2020.
As above only.
|Roberts, T.R. and Stewart, D.J.||Journal Article||1976||An ecological and systematic survey of fishes in the rapids of the lower Zaire or Congo river|
|Mo, T.-P.||Journal Article||1991||Anatomy and systematics of Bagridae (Teleostei) and siluroid phylogeny|
|Geerinckx, T., Vreven, E.J., Dierick, M., van Hoorebeke, L. and Adriaens, D.||Journal Article||2013||Revision of Notoglanidium and related gerera (Siluriformes: Claroteidae) based on morphology and osteology|
|Stiassny, M.L.J., Monsembula Iyaba, R.J.C., Liyandja, T., Mbimbi Mayi Munene, J.J., Yoko, M., and Alter, E.||Conference Paper||2018||The evolution of extreme phenotypic convergence across fish lineages in the hyper-diverse Lower Congo River|
|Stiassny, M.L.J.||Journal Article||2019||Fishes in the lower Congo River An extreme case of species divergence and convergent evolution|
|Elbein, A.||Web Page||2020||Earth’s deepest river conceals an evolutionary mystery|