Distichodus langi Nichols and Griscom, 1917

Moelants, Tuur, Zebe, Victorine Mbadu, Snoeks, Jos & Vreven, Emmanuel, 2014, A review of the Distichodus antonii assemblage (Characiformes: Distichodontidae) from the Congo basin, Journal of Natural History 48 (27 - 28), pp. 1707-1735 : 1726-1731

Distichodus langi Nichols and Griscom, 1917

( Tables 4 and 5; Figures 3C and 8 )

Type material

Holotype. AMNH 5915 , Faradje , Dungu region ( DRC) (± 3°44′ N, 29°43′ E) (364 mm SL).

Note on the original description. Distichodus langi has been described by Nichols and Griscom in 1917 based on one type from Faradje and one other specimen with the same data. The current holotype has a size of 364 mm SL (472 mm TL), which does not correspond to the 510 mm SL mentioned by Nichols and Griscom (1917). This latter SL should be considered a lapsus because after verification of the Lang and Chapin collection, no D. langi specimen of this size has been found. The other specimen mentioned in the original description is reported to measure 325 mm SL, but this also does not correspond to the size of the other specimen ( AMNH 7010), which measures 250.7 mm SL, 299.0 mm TL. This specimen has been wrongfully assigned paratype status ( Eschmeyer 2013) (see ICZN 1999: article 72.4.6). It has been re-identified as D. fasciolatus in this review (see above). In the original description, the size of the illustrated specimen ( Nichols and Griscom 1917: plate LXIX) is mentioned as 560 mm TL, which corresponds to a recalculated standard length of 466 mm SL. This does not correspond to either of the two specimens mentioned by Nichols and Griscom (1917). In addition, the drawing does not resemble either of the two specimens. Based on the following counts and observations made on the illustration: 22 circumpeduncular scales; 13 scales between the LL and the dorsal fin, 24 dorsal fin rays and clearly black ventral fins, we assume this illustration represents a specimen from the D. atroventralis complex.

Other material examined

MRAC 2878 , Avakubi ( DRC) (1°19′ N, 27°33′ E) (300 mm SL) .

Differential diagnosis

Within the Congo basin, D. langi can be distinguished from D. affinis , D. altus , D. decemmaculatus , D. noboli , D. notospilus and D. teugelsi by its higher total number of LL scales, i.e. 68–70 (versus <46); from D.maculatus by the absence of large, dark spots all over the body and a higher number of dorsal fin rays, i.e. 26–28 (versus 19– 21); from D. antonii by its inferior (versus terminal) mouth, its higher number of scales between the LL and the dorsal fin, i.e. 15–16 (versus 10–12) and its higher number of LL scales in front of HJ, i.e. 68–70 (versus 52–64); from D. fasciolatus by its higher number of dorsal fin rays, i.e. 26–28 (versus 24–26); its higher number of pelvic fin rays, i.e. 11 (versus generally 10) and its deeper head, 67.4–69.4 %HL (versus 35.9–62.9 %HL); from D.lusosso by its inferior (versus terminal) mouth and feebly compressed snout (versus distinctive prolonged); from D. sexfasciatus by its feebly compressed snout (versus strongly compressed), its higher number of dark vertical bars along the body, i.e. 13 (versus 6–7) and its higher number of teeth on the outer row on both jaws (> 20 versus 12–14) and from the D. atroventralis complex by a higher number of scales between the LL and pelvic fin, i.e. 12 (versus 9–11), its higher number of pectoral fin rays, i.e. 21 (versus 17–20); its higher number of circumpeduncular scales, i.e. 24–25 (versus 20–24) and its deeper head, 67.4–69.4 % HL (versus 35.1–55.7 %HL) ( Table 4).

Description

Morphometric and meristic data are given in Table 5. Body relatively deep (within D. antonii assemblage). Dorsal head profile and dorsal body outline concave to end of dorsal fin, straight from end of dorsal to adipose fin, and convex from adipose to caudal fin. Ventral head profile straight, concave from posterior to head to end of anal fin, and convex from end of anal to caudal fin. Head compressed with nasal openings relatively closely set (14.4 %HL and 15.9 %HL), but deep (67.4 %HL and 69.4 %HL). Mouth inferior. Posterior edge of maxillary not passing the nostrils. Two rows of bicuspid teeth in each jaw. Origin of dorsal fin well in front of pelvic fin origin along vertical axis. Distal margin dorsal fin straight or slightly concave, distal margin of anal fin straight to slightly convex. Base and distal end of pelvic fin relatively close to vent, i.e. 23.4 %SL and 25.9 %SL, and 1.6 %SL and 7.8 %SL, respectively. Pectoral and pelvic fin rays decreasing in length from outer to inner fin margin. Adipose fin little further removed from dorsal fin than from caudal fin. Caudal peduncle deeper then long. Caudal fin forked with two rounded lobes covered with numerous small scales except for translucent area distally. As only two specimens are currently known from D. langi , allometry could not be assessed.

Maximum recorded length: 364 mm SL, 472 mm TL.

Colouration

Lang provided information on the presumable life colour pattern based on five specimens ( Nichols and Griscom 1917). It is however unsure whether these specimens are conspecific (see above), and therefore this information is not presented here.

The body of the two preserved specimens is uniformly brown-yellowish, with a slightly lighter belly. Dorsal fin scattered with many small, dark spots. Caudal fin brownish, with slightly darker median rays. Adipose fin with translucent distal margin ( Figures 3C and 8 ). Pectoral fins pale to yellow-orange. Pelvic fins generally pale, while in the additional specimen the distal edges are darker coloured. Thirteen vague dark vertical bars have been observed on the flanks of the additional specimen, whereas the holotype has none.

Ecology

Not much is known about the ecology of D. langi . In the original description of Nichols and Griscom (1917), Lang is cited mentioning the following: “Evidently swimming in schools, as five of them have been killed by one explosion”. However, since this original description is based upon three different species (see above), the relevance of this information is difficult to assess.

Distribution

This species is only known from two specimens from two different locations, Faradje in the Dungu region , Uele River basin ( DRC) and Avakubi, Aruwimi River basin ( DRC) ( Figure 5 ) .

Etymology

The species name “ langi ” refers to the collector Herbert Lang (1879–1957), who collected fish in the Congo basin from 1909 to 1915 for the AMNH, in collaboration with James Chapin ( Slack 2003).

List of specimens examined of the D. atroventralis complex (all lengths are SL) ( Figure 3D ).

Democratic Republic of the Congo (DRC): Syntypes: MRAC 30 . Boma ( DRC) (± 5°50′ S, 13°03′ E), coll. Wilverth 1896 (70.9 mm) – BMNH 1891.12 .29.13. Congo River , Lower Congo ( DRC), received from Utrecht University Museum 1891 (63.5 mm); Specimens : AMNH I-243645 . Lulua River , Katende 2, Dipumu (± 6° 00′27.0″ S, 22°23′43″ E), coll. Mbimbi 01/12/2007 (64.2 mm; 90.2 mm) – AMNH I-243646 . Lulua River , Nsanga Nyembo (± 5°56′53.41″ S, 22°20′29.40″ E), coll. Mbimbi 03/12/2007 (76.7 mm; 123.3 mm) – AMNH I-247823 . Lulua , Bunkonde (6°14′49.2″ S, 22°28′48.0″ E), coll. Mbimbi 30/06/2008 (34.4 mm) – AMNH I-247825 . Lulua , Katende 1, Nkombua (6°00′16.2″ S, 22°23′25.8″ E), coll. Mbimbi 21/05/2008 (37.0 mm) – MRAC 158797 . Dundo , affl. Luachimo (± 7°21′ S, 20°50′ E), coll. De Barros Machado 02/06/1949 (225.5 mm) – MCZ 50439. Zaire River near Inga, a few km upstream and on the opposite side of river from Inga hydroelectric dam (5°27′30″ S, 13°36′??″ E), coll. Roberts and Stewart 1973 (53.2 mm; 62.8 mm) – MRAC 738 . Banana (6°00′ S, 12°24′ E), coll. Delhez 1899 (53.5 mm) – MRAC 739 . Matadi (5°49′ S, 13°27′ E), coll. Delhez, 1899 (246.6 mm) – MRAC 740 . Matadi (5°49′ S, 13°27′ E), coll. Delhez 1899 (66.0 mm) – MRAC 741 . Dolo (4°19′ S, 15°19′ E), coll. Delhez 1899 (357.0 mm) – MRAC 742 . Kutu , (± 2°44′ S, 18°08′ E), coll. Delhez 1899 (158.3 mm) – MRAC 67444 . Léopoldville (± 4°18′ S, 15°18′ E), coll. Henri van Moorsel 7/1944 (127.7 mm) – MRAC 117366 . Stanley Pool , Yankau channel, N’ Duka indigenous dam (± 4°20′ S, 15°24′ E), coll. Mission Brien-Poll-Bouillon 23/ 9/1957 (199.5 mm) – MRAC 73-22 -P-1195-1197. Stanley Pool , Nsele river (± 4°15′ S, 15°33′ E), coll. Mandeville 29/10/1957 (23.8–41.2 mm) – MRAC 73-22 -P-1201-1202. Stanley Pool , Ndjili river (± 4°20′ S, 15°22′ E), coll. Mandeville 30/10/1957 (67.8 mm; 76.8 mm) – MRAC 73-22 -P-1223. Stanley Pool , Mbamu island (± 4°14′ S, 15°22′ E to ± 4°18′ S, 15°30′ E), coll. Mandeville J., 28/10/1957 (33.1 mm) – MRAC A7-014 -P- 0025. Pool Malebo at Kinkole, Mipongi island (± 4°16′26.9″ S, 15°30′29.6″ E), coll. Mbadu Zebe 26/1/2006 (128.0 mm) – MRAC A7-033 -P-267. Congo River close to the Kinsanga channel, Inga (± 5°39′ S, 13°39′ E), coll. Hanssens 2007 (142.6 mm) – MRAC B0-017-P-0020. Lomami River , affluent Congo River, village Lieki, coll. Congo 2010 2/06/2010 (343.0 mm) – MRAC B0-017-P-0021-0022. Isangi , rive gauche fleuve Congo, coll. Congo 2010 5/06/2010 (261.9 mm SL; 325.0 mm SL) – MRAC B0-017-P-0093. Lomami River , left bank, just downstream of village Lieki (± 0°40′55″ N, 24°11′08″ E), coll Exp. Congo 2010 27/05/2010 (31.5 mm) – MRAC B0-017-P-0094. Little marsh on Lomami River, left bank, upstream of village Yandjambi (± 0°41′57.44″ N, 24°13′36.0114″ E), coll Exp. Congo 2010 28/05/2010 (31.4 mm) – MRAC B0-017-P-0095. Lomami River , left bank, upstreamof village Lieki (rive gauche riv. Lomami, en amont du village Lieki (± 0°40′55″ N, 24°11′08″ E), coll Exp. Congo 2010 01/06/2010 (61.6 mm) – MRAC B0-017-0096-0097. Lomami River , right bank, downstream of village Lieki (± 0°40′ 55″ N, 24°11′08″ E), coll. Exp. Congo 2010 30/05/2010 (21.7 mm; 25.9 mm) – MRAC B0-017-P-0098. Lomami River , downstream of village Lieki (± 0°40′55″ N, 24°11′ 08″ E), coll Exp. Congo 2010 27/05/2010 (32.0 mm) – MRAC B0-017-0099-0100. Lomami River , downstream of village Lieki (± 0°40′55″ N, 24°11′08″ E), coll. Exp. Congo 2010 03/06/2010 (27.6 mm SL; 36.2 mm) – MRAC B0-017-P-0101. Lomami River at confluence with Koli River, right bank, downstream of village Lieki (± 0°40′ 55″ N, 24°11′08″ E), coll. Exp. Congo 2010 01/06/2010 (25.6 mm) – MRAC B1-009 - P-0022. Lobaye River , left bank, Site 2 (± 0°28′28.8″ N, 24°11′57.9″ E), village Bambondji II, coll. Danadu and Moelants 08/05/2011 (93.0 mm) .

Republic of the Congo (Brazzaville): MRAC A8-020 -P-0386-0390 (2/4). Léfini River , “Massala ma soso” rapids, right bank (2°55.93′ S, 16°07.42′ E), coll. Vreven and Ibala Zamba 23/8/2008 (46.5 mm; 68.5 mm) .

Figures

Figure 3. Illustrations of type specimens of the Distichodus antonii assemblage. (A) Holotype of D. antonii (BMNH 1899.9.6.10), 103.3 mm SL; (B) Lectotype of Distichodus fasciolatus (MRAC 23), 278.2 mm SL; (C) Holotype of Distichodus langi (AMNH 5915), 364 mm SL. Picture taken by M.L.J. Stiassny (AMNH); (D) Syntype of Distichodus atroventralis (BMNH 1891.12.29.13), 63.5 mm SL.

Figure 5. Distribution map of Distichodus antonii and Distichodus langi based on the specimens identified at the AMNH and MRAC. Note: Distichodus antonii: () holotype and (●) other specimens; D. langi: (*) lectotype and (*) specimen.

Figure 8. Distichodus langi (MRAC 2878) from Avakubi (DRC), 300.0 mm SL. (A) Lateral view; (B) Detail of the colour pattern on the adipose fin.