Haplochromis falcatus, Vranken & Steenberge & Heylen & Decru & Snoeks, 2022

Vranken, Nathan, Steenberge, Maarten Van, Heylen, Annelies, Decru, Eva & Snoeks, Jos, 2022, From a pair to a dozen: the piscivorous species of Haplochromis (Cichlidae) from the Lake Edward system, European Journal of Taxonomy 815, pp. 1-94 : 48-53

Haplochromis falcatus sp. nov.

urn:lsid:zoobank.org:act:B780DC12-8C55-4B57-98F1-5799201CD438

Figs 1–2 , 26–28 ; Table 1

Differential diagnosis

Species with a piscivorous morphology; outer oral teeth many, small, and strongly recurved [UOT 39– 51 (median 45)]; dominant males olive-green with an orange-red anterior part of flank and well-defined mid-lateral and dorsal-lateral bands.

Amongst piscivorous species from the Lake Edward system, H. falcatus sp. nov. differs from all except H. curvidens sp. nov. by strongly recurved vs straight to weakly recurved outer jaw teeth.

It further differs from H. latifrons sp. nov., H. rex sp. nov., H. simba sp. nov., and H. aquila sp. nov. by the combination of smaller outer oral teeth and a larger number of outer upper jaw teeth [UOT 39–51 (45) vs 22–42 (27–31)]; further from H. latifrons sp. nov., H. rex sp. nov., and H. simba sp. nov. by a shallower lacrimal [LaD 16.1–18.8 (mean 18.0) vs 18.7–23.0 (19.5–20.8) % HL]; further from H. rex sp. nov., H. simba sp. nov., and H. aquila sp. nov. by presence vs absence of well-defined mid-lateral and dorsal-lateral bands, and dominant males uniformly olive-green with an orange-red anterior part of flank vs cream-coloured with an orange operculum and light blue snout, uniformly yellow with an orange anterior part of flank, or light grey with a black head, respectively.

It further differs from H. mentatus and H. glaucus sp. nov. by the combination of a longer pre-dorsal distance [PrD 36.9–41.1 (39.5) vs 33.3–37.0 (35.3–36.1) % SL], a gentler lower jaw side (15–25° vs 30–45°), and presence vs absence of well-defined mid-lateral and dorsal-lateral bands; further from H. mentatus by a longer head [HL 36.6–39.6 (38.2) vs 33.4–37.0 (35.1) % SL]; further from H. glaucus sp. nov. by dominant males olive-green with an orange-red anterior part of flank vs uniformly light blue.

It further differs from H. kimondo sp. nov. by the combination of an oval vs pyriform body, a straight vs convex dorsal outline of head, shallower cheeks [ChD 23.3–27.4 (exceptionally 28.0 in one specimen) (mean 26.0) vs 27.1–35.2 (30.9) % HL], narrower jaws [LJW 40.2–45.6 (42.5) vs 44.7–53.3 (49.3) % LJL], and dominant males olive-green with an orange-red anterior part of flank vs grey dorsally and yellow ventrally.

It differs from H. curvidens sp. nov. and further differs from H. pardus sp. nov. by the combination of a deeper cheek [ChD 25.1–28.0 (exceptionally 23.3 in one specimen) (mean 26.0) vs 20.8–24.9 (22.5– 23.2) % HL] and a longer pre-dorsal distance [PrD 38.2–41.1 (exceptionally 36.9 in one specimen) (mean 39.5) vs 34.1–37.9 (36.0–36.3) % SL]; further from H. curvidens sp. nov. by presence vs absence of well-defined mid-lateral and dorsal-lateral bands; further from H. pardus sp. nov. by larger adult size (max. 137 vs 96 mm SL) and colour pattern of small specimens (<100 mm SL) light coloured vs speckled to uniformly black.

It further differs from H. quasimodo sp. nov. and H. squamipinnis by the combination of a longer head [HL 36.6–39.6 (38.2) vs 33.9–37.2 (35.5–36.0) % SL], a shorter pelvic fin [VL 21.6–25.7 (23.5) vs 25.2–35.4 (28.8–29.4) % SL], and dominant males olive-green with an orange-red anterior part of flank vs light grey dorsally and blue-black ventrally or slate blue, respectively; further from H. squamipinnis by absence vs presence of minute scales on proximal parts of dorsal and anal fin.

Etymology

Specific name from the Latin ‘ falcatus ’ for ‘sickle-shaped’; referring to acutely pointed sickle-like outer oral teeth.

Material examined

Holotype UGANDA • ♂, 101.3 mm SL; Lake Edward, Kayanja offshore; 0°05′31.2″ S, 29°45′30.3″ E; 21 Jan. 2018; HIPE3 exped. leg.; RMCA 2018.008.P.0401 .

Paratypes DEMOCRATIC REPUBLIC OF THE CONGO • 1 ♀, 136.8 mm SL; “Lac Edouard: riv. Luniasenke” [Lake Edward: Luniasenke River ]; 0°27′19.2″ S, 29°22′08.7″ E (inferred); 04 Jan. 1953; KEA exped. leg.; IRSNB 13469 • 1 ♀, 137.1 mm SL; “Lac Edouard: ½h à l’Ouest d’Ishango” [Lake Edward: ½ hour west of Ishango ]; 0°08′14″ S, 29°38′23″ E (inferred); 27 Mar. 1953; KEA exped. leg.; IRSNB 13473 .

UGANDA – Lake Edward • 1 ♂, 2 ♀♀, 98.6–112.8 mm SL; 1 km east of Nyamugasani River ; 0°10′22.8″ S, 219°50′13.2″ E; 22 Oct. 2016; HIPE1 exped. leg.; sand substrate; RMCA 2016.035.P.0256 to 0258 • 1 ♀, 110.8 mm SL; mouth of Kazinga Channel ; 0°12′14.4″ S, 29°52′37.2″ E; 23 Mar. 2017; HIPE2 exped. leg.; hard substrate; RMCA 2017.006.P.0415 • 1 ♂, 1 ♀, 119.1–120.7 mm SL, no morphometrics taken; 0°24′16.0″ S, 29°46′24.8″ E; 25 Mar. 2017; HIPE2 exped. leg.; bought at Rwenshama landing site; RMCA 2017.006.P.0416 to 0417 • 1 ♀, 81.3 mm SL; Kayanja offshore; 0°05′34.8″ S, 29°45′28.8″ E; 30 Mar. 2017; HIPE2 exped. leg.; RMCA 2017.006.P.0418 • 2 ♀♀, 81.6, 93.8 mm SL; Kayanja offshore; 0°05′34.8″ S, 29°45′28.8″ E; 30 Mar. 2017; HIPE2 exped. leg.; RMCA 2017.006.P.0419 to 0420 • 3 ♀♀, 75.0– 109.6 mm SL; Kayanja offshore; 0°05′34.8″ S, 29°45′28.8″ E; 31 Mar. 2017; HIPE2 exped. leg.; RMCA 2017.006.P.0421 to 0423 • 1 ♂, 1 ♀, 88.5–103.3 mm SL; Kayanja , offshore; 0°05′31.2″ S, 29°45′30.3″ E; 20 Jan.2018; HIPE3 exped. leg.; RMCA 2018.008.P.0397 to 0398 • 2 ♂♂, 102.1–110.4 mm SL; Kayanja , offshore; 0°05′31.2″ S, 29°45′30.3″ E; 21 Jan. 2018; HIPE3 exped. leg.; RMCA 2018.008.P.0399 to 0400 • 1 ♀, 93.5 mm SL; same collection data as for preceding; RMCA 2018.008.P.0402 • 2 ♀♀, 110.9–114.2 mm SL; 0°24′16.0″ S, 29°46′24.8″ E; 24 Jan. 2018; HIPE3 exped. leg.; bought at Rwenshama landing site; RMCA 2018.008.P.0403 to 0404 .

Description

Based on 22 specimens (75.0– 137.1 mm SL); body shallow ( Table 1 ) and oval ( Fig. 26 ). Head very long, narrow, and with a straight dorsal outline; eye small; interorbital area narrow; cheek and lacrimal average in depth. Snout long, acute, and slopes gently at 35–45°; premaxillary pedicel long and strongly prominent. Jaws isognathous to slightly prognathous, long, slim, narrow, and rounded in dorsal view; gape large and slopes gently at 20–30°; maxilla extends to vertical through pupil. Lower jaw shallow and with a straight ventral outline in lateral view, mental prominence absent, and lower jaw side nearly flat with an inclination of 15–25° to horizontal in anterior view; lower jaw expands slightly laterally halfway its length. Upper jaw weakly expanded anteriorly. Lips and oral mucosa large. Neurocranium shallow, ethmo-vomerine block decurved, preorbital region very shallow (18–22% NL), orbital region shallow (28–30% NL), and supraoccipital crest average in depth and wedge-shaped ( Fig. 27b ).

Outer oral teeth numerous, unicuspid, and relatively small. Necks stout, conical, and recurved; crowns recurved to strongly recurved, and acutely pointed. Dental arcades rounded, and with anterior half expanded laterally. Outer teeth closely and regularly set with neck-distances of ½–1 neck-width. No enlarged teeth posterior in upper jaw. Inner teeth small, strongly recurved, unicuspid, and acutely pointed. Tooth bands very slender crescent-shaped with 1–2 rows of inner teeth, and narrow posteriorly until only outer row remains past ⅔ lengths of tooth bands. Inner teeth closely and regularly set on ½–1 neck-width from outer row in lower jaw, on 1–2 neck-widths from outer row in upper jaw; implantation recumbent; size uniform throughout tooth band.

Lower pharyngeal bone average in length, triangular, slim, and shallow with a slightly deeper keel ( Fig. 28 ). Pharyngeal teeth relatively large and slender; major cusps acutely pointed; cusp gaps straight; minor cusps and cusp protuberances very small. Teeth in two median longitudinal rows equal in size and form to lateral teeth, 10 in each row. Posterior transverse row with 16–21 teeth, implanted erectly with a lateral inclination; major cusps weakly recurved, bluntly pointed, and laterally compressed; minor cusps mostly absent.

Chest scales small; transition to larger flank scales gradual. Minute scales on proximal half of caudal fin.

Caudal fin subtruncate; dorsal and anal fins reach to vertical through caudal-fin base. Pectoral fin reaches to between genital opening and first anal-fin spine; pelvic fin reaches to between genital opening and first anal-fin spine in females, to first anal fin branched ray in males; first branched pelvic-fin ray elongated in dominant males.

Ceratobranchial gill rakers in outer row of first gill arch very short, stout, and simple; posteriormost rakers weakly anvil-shaped. Epibranchial gill rakers relatively slender and simple.

Colouration in life

Dominant males: body olive-green with yellow sheen; anterior part of flank and operculum bright orange-red; belly and chest speckled black ( Fig. 27c ). Cheek olive-green with red sheen; snout and lips dusky; lower lip with blue sheen; branchiostegal membrane black; eye with dark silver outer ring and silver to golden inner ring. Flank with well-defined mid-lateral and dorsal-lateral bands; dorsum with 5–7 faint vertical stripes between dorsal-fin base and dorsal-lateral band. Lacrimal, nostril, and interorbital stripes and a mental blotch well defined; supraorbital stripe and nape band faint. Pectoral fin hyaline; pelvic fin black; dorsal fin dusky and with black lappets; anal fin faint orange-red and with dusky base and posterior part, and 3 small yellow egg spots with hyaline rings. Caudal fin with dusky base and hyaline distal part. Non-dominant males: similar to dominant males except for white belly and chest and faint orange-red antero-dorsal part of flank above mid-lateral band.

Females and juveniles: body, operculum, cheek, and lacrimal olive-green yellow; belly, chest, and lower jaw white; eye with dark silver outer ring and silver to golden inner ring ( Fig. 27d ). Flank with welldefined mid-lateral and dorsal-lateral bands; dorsum with 5–7 faint vertical stripes between dorsal-fin base and dorsal-lateral band. Lacrimal, nostril, and interorbital stripes and a mental blotch well defined; supraorbital stripe and nape band faint. Pectoral and pelvic fins yellowish; dorsal fin dusky and with black lappets; anal fin yellow and with 2–3 small spots resembling egg spots; caudal fin dusky.

Preserved colouration

Dorsal part of body brown; ventral part of body yellowish to white in females; chest and belly speckled black in dominant males ( Fig. 27a ). Cheek yellowish and snout dusky. Flank with well-defined midlateral and dorsal-lateral bands; dorsum with 5–7 faint vertical stripes between dorsal-fin base and dorsallateral band. Lacrimal, nostril, and interorbital stripes and a mental blotch well defined; supraorbital stripe and nape band faint. Pectoral fin dusky; pelvic fin dusky in females, black in dominant males; dorsal fin dusky and with black lappets; anal fin with dusky base and posterior part, yellowish distal part, and 1–3 small egg spots; caudal fin dusky and faintly maculated in dorsal part.

Distribution and ecology

Only known from Lake Edward, found over sandy substrates. Based on its morphology, most probably a piscivorous species.

Figures

Fig. 1. The Lake Edward system, consisting of Lakes Edward and George that are connected through the Kazinga Channel. The catch localities of all examined specimens are indicated: Haplochromis sp. ‘latifrons’ (), H. mentatus Regan, 1925 (), H. sp. ‘rex’ (), H. sp. ‘simba’ (▼), H. sp. ‘glaucus’ (), H. sp. ‘aquila’ (), H. sp. ‘kimondo’ (●), H. sp. ‘falcatus’ (), H. sp. ‘curvidens’ (), H. sp. ‘pardus’ (), H. sp. ‘quasimodo’ (▲), and H. squamipinnis Regan, 1921 (█). The type localities of H. mentatus and H. squamipinnis are not shown as the exact locations are unknown.

Fig. 2. a. Differences in total number of outer teeth and premaxillary dentition between the macro- and microdontic groups of piscivores from the Lake Edward system.b. Schematic presentation of the dominant male colour patterns in life, in the various groups studied. For H. sp. ‘latifrons’ the female and for H. sp. ‘curvidens’ the non-dominant colour patterns are shown, as those of dominant males are unknown.

Fig. 26. Haplochromis falcatus sp. nov., holotype, ♂, 101.3 mm SL (RMCA 2018.008.P.0401). Drawn by N. Vranken.

Fig. 27. Haplochromis falcatus sp. nov. a. Photograph of preserved holotype (RMCA 2018.008.P.0401; 101.3 mm SL). b. X-ray image of holotype. c–d. Photographs of freshly caught specimens. c. Dominant male (RMCA 2017.006.P.0416; 119.1 mm SL). d. Female (RMCA 2016.035.P.0257; 112.8 mm SL) to illustrate the live colour patterns. The contrast was slightly enhanced.

Fig. 28. Haplochromis falcatus sp. nov. (RMCA 2018.008.P.0397; 103.3 mm SL). a. Dorsal view of the lower pharyngeal jaw. b. Lateral view of the lower pharyngeal jaw.