Congochromis rotundiceps, Wingi & Schliewen, 2022

Wingi, Nadine Usimesa & Schliewen, Ulrich Kurt, 2022, Congochromis rotundiceps sp. nov., a new cichlid species (Actinopterygii: Cichlidae) from the Congo Drainage, Zootaxa 5124 (3), pp. 296-320 : 307-312

Congochromis rotundiceps sp. nov.

Holotype. MRAC 192224–232 , female (1, 49.71mm SL) Stanley-Pool [Malebo Pool], 1967, no GPS data available; Democratic Republic of Congo (Kinshasa).

Paratypes. MRAC –PIS–192233, male (1, 52.65mm SL); Stanley-Pool [Malebo Pool], no GPS data available, Democratic Republic of Congo (Kinshasa). coll. J. Lambert. — MRAC 192224–232 , females (8, 40.2251.54mm SL; Stanley-Pool [Malebo Pool], no GPS data available, Democratic Republic of Congo (Kinshasa).

Generic assignment. The new species shares all diagnostic character states identified for the genus Congochromis ( Stiassny & Schliewen 2007) : (1) four pores in the dentary laterosensory canal; (2) absence of a laterosensory canal in the angulo-articular, (3) six pores in the preopercle laterosensory canal; (4) a single tubular infraorbital bone behind the lachrymal; (5) 12 circumpeduncular scales; (6) jaw teeth relatively robust unicuspids, not closely spaced; and (7) the presence of a small, supraneural bone.

Differential diagnosis. Congochromis rotundiceps sp. nov can be distinguished from other species of the genus Congochromis by the following characters: from C. robustus by having no scale rows vs. two scale rows on cheek, more scales in the horizontal line (25 vs. 24), more dorsal-fin spines (17–18 vs. 16), fewer lower (procurrent) caudal-fin rays (5–6 vs. 7), fewer caudal-fin rays (25–26 vs. 27), in the position of the pterygiophore supporting the last dorsal-fin spine (at vertebrae count: 16–17 vs. 15), and in the position of the pterygiophore supporting the last dorsal-fin spine above caudal vertebrae vs. above abdominal ones. It further differs from this species by a larger interorbital width (28.3–32.1% HL vs. 26.2–28.23% HL), a larger eye diameter (31.4–35.1% HL vs. 23.5–24.6% HL), a shorter snout length (29.8–32.7% HL vs. 33.8–38.5% HL), a shorter upper lip length (29.2–32.0% HL vs. 33.0–37.0% HL), a shorter lower lip length (26.2–33.6% HL vs. 33.7–37.6% HL), a shorter lower lip width (27.7–31.2% HL vs.36.1–40.5% HL), a shorter predorsal distance (23.6–28.7% SL vs. 30.8–33.0% SL), a longer third anal-fin spine length (14.7–16.7% SL vs. 11.4–13.8% SL), a shorter caudal peduncle depth (12.8–13.6% SL vs. 15.8–17.2% SL), a shorter caudal peduncle (11.7–12.7% SL vs. 14.0–14.8% SL), a smaller body depth (25.1–26.3% SL vs. 29.5–31.5% SL), and a shorter intrapectoral width (11.3–12.7% SL vs. 16.7–17.2% SL). Congochromis rotundiceps sp. nov differs from Congochromis pugnatus by having a larger preorbital width (39.0–41.5% HL vs. 32.3–29.7% HL), a shorter snout length (29.8–32.7% HL vs. 32.7–35.0% HL), a larger eye diameter (31.4–35.1% HL vs. 26.7–29.7% HL), a shorter lower lip length (26.1–33.6% HL vs. 34.8–39.9% HL), a shorter lower lip width (27.7–31.2% HL vs. 32.5–37.9% HL), a longer last dorsal-fin spine length (12.6–13.2% SL vs. 8.8–10.1% SL), a shorter anal-fin length (15.3–16.9% SL vs. 14.7–18.2% SL), a longer third anal-fin spine length (14.7–16.7% SL vs. 11.6–13.7% SL), a shorter caudal-peduncle (11.7–12.7% SL vs. 14.0–15.5% SL), and a shorter body depth (25.1–26.3% SL vs. 27.8–29.8% SL).

The new species differs from Congochromis dimidiatus by a larger interorbital width (28.3–32.1% HL vs. 23.8–28.2% HL) and a larger preorbital width (39.0–41.5% HL vs. 32.3–38.5% HL). It differs from Congochromis sabinae by having a larger interorbital width (28.3–32.1% HL vs. 21.8–25.7% HL), by featuring an ocellus-like spot in the soft-rayed part of the dorsal-fin, a longer preorbital width (39.0–41.5% HL vs. 31.6–36.3% HL), a shorter caudal-peduncle (11.7–12.71% SL vs. 13.29–19.04% SL), and a shorter body depth (25.05–26.33% SL vs. 27.20–33.72% HL). It differs from Congochromis squamiceps by a longer preorbital width (39.0–41.5% HL vs. 29.0–38.6% HL) and a shorter anal-fin length (15.3–16.9 vs. 17.7–23.3% SL).

Description. Morphometric measurements and meristic characters based on 10 type specimens (one male and nine females). Values and corresponding ranges are presented in Table 2 . For general appearance see Figs. 6 and 7 .

Maximum recorded length of a male specimen with 72.5mm (52.7mm SL), largest female with 67.5mm TL (52.6mm SL). Maximum body depth (25.1–26.3% SL) at level of dorsal-fin origin. Caudal fin rounded in both sexes. Caudal peduncle as long as deep (2.19–2.21; 1.88–2.06). Head length about one third of standard length (32.9–34.8% HL). Dorsal head profile moderately curved. Eye diameter (31.4–35.1% HL) larger than interorbital width (28.3–32.1% HL) and slightly larger than snout length (29.8–32.7% HL). Jaws isognathous. Posterior tip of maxilla reaching anterior margin of orbit. Two separate lateral lines.

Squamation. Flank above and below lateral lines covered with comparatively large cycloid scales. Belly with comparatively small cycloid scales. Check and snout scaleless. Cycloid scales on chest small, ventral part of the chest (anterior of pelvic-fin scales) with few deeply embedded scales. Opercle without or with two cycloid scales on vertical line starting from end of posterior-dorsal angle of operculum to anterior edge of operculum; if present cycloid. Upper lateral line with 16–20 scales (including interrupting unpored scales in the count) and lower lateral line with 4–7 pored scales. Horizontal line scales with 25 scales. Upper lateral line and lower lateral line not overlapping. Upper lateral line and horizontal line separated by two scales rows on level of last dorsal-fin spine. Four scales between upper lateral line and dorsal-fin origin. One scale between lateral line and last dorsal-fin spine. Twelve scales around caudal peduncle.

Jaws and dentition. Shape of the dental arcade rounded. Teeth of outer tooth rows unicuspid and widely set, towards mouth angled teeth slightly smaller and more closely set. Individual teeth strongly recurved with brownish crown; tips pointed. Two inner tooth rows in upper and lower jaw; teeth unicuspid and only slightly smaller than teeth of outer tooth rows. Outer row upper jaw with approximately 50 teeth and outer row lower jaw with approximately 34 teeth (specimen MRAC–PIS–192224–232 #5: 50.05mm SL).

Lower pharyngealbone length ( Fig. 8 ) of the single dissected specimens (MRAC–PIS–192224–232 #5 measures 3.82 mm and lower pharyngeal widths bone 21.98% (0.84 mm) of lower pharyngeal bone length. Dentigerous area lengths measures 0.42 mm and dentigerous area widths, 1.92 mm. Dentigerous area of lower pharyngeal with 14+12 teeth along posterior margin and 3–4 teeth along midline.

Gill rakers. Total gill raker count 12–15, with 3–4 epibranchial, one on angle (cartilaginous plug), and 8–10 ceratobranchial gill rakers. Most anterior (ventral) ceratobranchial gill rakers very small and increasing in size towards cartilaginous plug (angle). Gill raker in angle slightly shorter or as long as longest epibranchial raker. Epibranchial gill rakers pointed and creatobranchial gill rakers tuberculate and blunt.

Fins. Dorsal-fin with 17–18 spines and 8–9 rays. First dorsal-fin spine always shortest. Dorsal-fin base length between 25.4–33.8% SL. Posterior end of dorsal-fin rays ending at caudal-fin base or slightly behind; posterior tip of anal-fin ending slightly at caudal-fin base (for females) or slightly behind (for male). Caudal-fin outline rounded and fin comprised of altogether 25–27 rays (one articulating on parhypural, seven on hypuralia 1+2, 7–8 on hypuralia 3+4+5, 4–5 upper procurrent caudal-fin rays and 5–6 procurrent caudal-fin). Anal fin with three spines (third spine longest) and 6–7 rays. Anal-fin base length between 15.3–16.9% SL. Pectoral-fin length between 20.5 and 23.0% SL, longest pectoral ray not reaching level of anus (i.e., ending approximately slightly behind midway pectoral-fin basis to level of anus). First upper and lower pectoral-fin rays short. Pelvic-fin base slightly posterior of pectoral-fin base. Pelvic-fin longer than pectoral-fin (19.98–28.91% SL vs. 20.5–23.0% SL).

Vertebrae and caudal fin skeleton. A total of 25–27 vertebrae (excluding urostyle element), with 13–15 abdominal and 11–13 caudal vertebrae. The pterygiophore supporting the last dorsal-fin spine inserted between neural spines of the 16 th and 17 th vertebra (counted from anterior to posterior). The pterygiophore supporting the last anal-fin spine inserting between haemal spines of the 15 th and 16 th or rarely between 16 th and 17 th vertebrae. A single predorsal bone (= supraneural bone) present. Hypurals 1 and 2 fused, or base not fused but remaining merged; hypurals 3 and 4 either fused into a single unit or separated.

Coloration.All available specimens were preserved in alcohol more than 30 years ago and and their pigmentation is largely faded. Since no coloration data were recorded by Lambert, the collector, almost no data on live coloration are available. The overall coloration of the specimens (see female Fig. 6 and male: Fig. 7 ) is whitish-pale beige. Eyes blackish. Snout light greyish. Belly and chest pale light brown to light beige. Lips light beige. A brown blotch on the operculum. Fins translucent whitish-beige. Highly conspicuous is, however, a single ocellus with a white margin and dark brown center in the soft-rayed part of the dorsal fin.

Sexual dimorphism. The single male is the largest specimen and slighly more elongated than females. It is an apparently mature male with 72.5mm SL contrasting with mature females some with a swollen belly of 54.5– 67.5mm SL. Caudal-fin is rounded in both sexes. Dorsal- and anal-fin rays more elongated in single available male than in females. Longest pelvic-fin ray reaching anus in male (25.93% SL vs. 16.40–22.33% SL).

The only available male specimen of this species differs from the females by a longer standard length (52.65 vs. 54.52–67.54), by a longer lower lip width (34.33 vs. 27.89–33.88% HL), a longer anal-fin length (19.43 vs. 14.81–17.14% SL), a longer pelvic-fin length (25.93 vs. 16.40–22.33% SL), a longer caudal peduncle depth (13.60 vs.12.63–13.45% SL), a longer caudal peduncle length (13.35 vs. 11.65–12.70% SL), a longer distance anus analfin (5.93 vs. 5.00–5.69% SL). The soft dorsal and anal rays of the male are longer than those of the females. Longest pelvic-fin ray reaching anus for the male.

Etymology. The species name rotundiceps refers to the widely rounded head of the new species by combining the latin adjective rotundus, meaning “round”, with the latin suffix - ceps, meaning “-headed”. A direct translation of rotundiceps is round headed. An adjective.

Distribution and biology. Specimens of Congochromis rotundiceps sp. nov. were deposited by J. Lambert in the Africa Museum, and the geographical origin of the specimens was given as “Stanley-Pool” [Malebo Pool], unfortunately without any further detail. Despite the many Congochromis and Nanochromis collections deposited from the Malebo Pool area close to Kinshasa or from the Cuvette Centrale area upstream of Malebo Pool in the Africa Museum (Tervuren) and in other museum collections, no additional specimens of the new species were found. We thus caution, that the exact location of origin of the type specimens might rather be a little explored specific location in the greater Malebo Pool area than the well explored Malebo Pool itself.

Figures

FIGURE 6. Congochromis rotundiceps sp. nov. holotype, preserved. A. Holotype (MRAC 192224-232 #1) Female. B. Radiograph of holotype. C. Drawing of paratype by Ruth Kühbandner (MRAC 192224-232 #5 (42.13mm SL)).

FIGURE 7. Congochromis rotundiceps sp. nov paratype, preserved. A. Paratype (MRAC 192233) Male. B. Radiograph of the same specimen.

FIGURE 8. Pharyngeal jaw and dentition of Congochromis rotundiceps sp. nov. A. Lower pharyngeal bone (MRAC 192224- 232 #7), specimen with 50.3mm SL. B. Overview of arrangement and morphology of oral jaw teeth, specimen with 49.7mm SL (MRAC 192224-232 #4).