Palaeoplex palimpsest, Schedel & Kupriyanov & Katongo & Schliewen, 2020

Schedel, Frederic D. B., Kupriyanov, Viviane M. S., Katongo, Cyprian & Schliewen, Ulrich K., 2020, Palaeoplex gen. nov. and Lufubuchromis gen. non, two new monotypic cichlid genera (Teleostei: Cichlidae) from northern Zambia, Zootaxa 4718 (2), pp. 191-229 : 201-209

Palaeoplex palimpsest , new species

Pseudocrenilabrus philander (non Weber), Balon et al. 1983

Chetia mola (non Balon & Stewart), Friedmann et al. 2013

New Kalungwishi cichlid; Weiss et al. 2015, Schedel et al. 2019

Orthochromis sp. “New Kalungwishi” Meier et al. 2019

Holotype. ZSM 47492, ex ZSM 44438 (7 in lot, now 6), 143.4 mm SL; Zambia, Luongo River, at bridge on road Kawambwa-Mansa about 40 km [driving distance] S of Kawambwa, Luapula Province (-10.144359 / 29.167193).

Paratype. ZSM 43077, 1 , 116.0 mm SL; Zambia, Drainage Congo; Luongo Reservoir, right bank above dam ~ opposite of Chisunka Luongo village, Luongo River 9 km above Musonda Falls on Luongo River , 56.5 km N of Mansa, Luapula Province (-10.685519 / 28.900466) .— ZSM 44438, 6 , 81.9–106.3 mm SL; Zambia, Drainage Congo; Luongo River , at bridge on road Kawambwa-Mansa about 40 km [driving distance] S of Kawambwa, Luapula Province (-10.144359 / 29.167193) .— ZSM 43079, 6 , 62.9–130.1 mm SL; Zambia, Drainage:Congo; Luongo Reservoir, right bank above dam ~opposite of Chisunka Luongo village, Luongo River 9km [air distance] above Musonda Falls on Luongo River , 56.5 km [air distance] N of Mansa, Luapula Province (-10.685519 / 28.900466) .— ZSM 43078, 1, 137.4 mm SL; Zambia, Drainage Congo; Luongo Reservoir, right bank above dam ~ opposite of Chisunka Luongo village, Luongo River 9 km above Musonda Falls on Luongo River , 56.5 km N of Mansa, Luapula Province (-10.685519 / 28.900466) .— CU 91755, 8, 50.0– 82.1 mm SL; Zambia, Drainage: Luongo River; Luongo River at Mukonshi Bridge on Mwenda-Kawanbwa road (-10.1442 / 29.167) .— CU 99504, 4, 39.5–100.8 mm SL; Zambia, Drainage Luongo River; Luongo River at bridge on Kashiba-Mwenda road (-10.4701 / 29.0245) .— SAIAB 208051 , 3 , ex ZSM 43077 (4 now 1), 102.8–122.8 mm SL; Zambia, Drainage Congo; Luongo Reservoir, right bank above dam ~ opposite of Chisunka Luongo village, Luongo River 9 km above Musonda Falls on Luongo River , 56.5 km N of Mansa, Luapula Province (-10.685519 / 28.900466) .— MRAC 2019.009 .P.0001-0003, 3, ex ZSM 43079 (9 now 6), 66.2–133.8 mm SL; Zambia, Drainage: Congo; Luongo Reservoir, right bank above dam ~ opposite of Chisunka Luongo village, Luongo River 9km [air distance] above Musonda Falls on Luongo River , 56.5 km [air distance] N of Mansa, Luapula Province (-10.685519 / 28.900466) .— ZSM 47493, ex ZSM 41496 (2 now 1), 1, 33.2 mm SL; Zambia, Drainage Congo; Luongo stream at bridge on road Mwenda-Kashiba, affluent to Lake Mweru / Upper Congo basin, Luapula Province (-10.470725 / 29.026200) .

Additional specimens examined. Palaeoplex palimpsest (specimens from Kalungwishi River): ZSM 41425, 6 , 73.0– 102.9 mm SL; Zambia, Drainage Congo; Kalungwishi stream above Lumangwe falls , W of Mukuma, on road Mukunsa—Kawambwa , approached from Northern Province (-9.543011 / 29.387789) .— ZSM 44357, 9 , 53.9–116.6 mm SL; Zambia, Drainage Congo; Kalungwishi River, 3 km below Kabwelume Falls [above Kundabwika Falls], ~ 23.5 km downstream bridge on road Mporokoso—Kawambwa , Northern Province (-9.502106 / 29.352734) .— SAIAB 77188 , (1 out of 5 specimens), 118.9 mm SL; Kundabwika falls on Kalungwishi River (-9.2179 / 29.3040) .

Diagnosis. Species diagnosis as for genus.

Description. Morphometric measurements and meristic characters are based on 34 type specimens. Values and their ranges are presented in Table 3 . For general appearance see Fig. 3 (male) and Fig. 4 (female). Maximum length of a wild caught male specimen 143.4 mm SL; largest female 110.7 mm SL. A rather deep bodied (BD: 28.9–36.0 % SL) species with maximum body depth slightly behind pelvic fin origin, decreasing towards caudal peduncle (dorsal margin of caudal peduncle roughly on level with dorsal margin of orbit). Ratio caudal peduncle length to depth: 1.2–1.8. HL about one third of SL. Adult males with a slightly concave upper head profile; females with a straight to slightly curved upper head profile. No prominent nuchal gibbosity. Jaws isognathous to slightly retrognathous. Posterior tip of maxilla reaching slightly behind nostril. Lips not noticeably enlarged or thickened. Two separate lateral lines.

Squamation. Flank and dorsum covered with comparatively large cycloid or weakly ctenoid (if ctenoid, ctenii very short; see Supplementary Fig. 2 ). Cycloid scales of belly slightly smaller than flank scales. Chest scales cycloid and smaller than belly scales, smallest behind branchiostegal membrane; chest to flank transition with slightly larger cycloid or weakly ctenoid scales. Snout scaleless. Medium sized interorbital scales cycloid; anteriormost scales partially embedded in skin. Nape and occipital region with slightly smaller cycloid scales compared to flank scales. Cheek covered with 2–4 scale rows of small to medium sized cycloid scales. One cycloid scale between posterior orbital margin and preoperculum. Operculum covered with cycloid scales of variable size, some almost size flank scales. Opercular blotch squamated to variable extent; posteriormost margin always scaleless. Three to five scales on horizontal line starting from anterior edge operculum to postero-dorsal edge operculum.

Scales on upper lateral line 16–24, lower lateral line 10–14 scales and horizontal line with 28–31 scales. Upper and lower lateral lines separated by two rows of scales. Five to nine scales between dorsal-fin origin and upper lateral line; 2–4 scales between origin last dorsal-fin spine and upper lateral line. Anterior caudal fin part covered with 2–4 ill-defined vertical columns of small cycloid scales including 0–2 pored scales; scaled area extending posteriorly to approximately 28–42 % caudal fin length with minute, interradial scales. Specimens from the Luongo River with 18–20 scales around caudal peduncle, specimens from Kalungwishi River with 16–18 scales around caudal peduncle.

Jaws and dentition.Anterior jaw teeth of outer rows of upper and lower jaw subequally bicuspid to subequilaterally bicuspid and closely set; towards corner of mouth, teeth are increasingly smaller and more widely set and might become unicuspid. Bicuspid teeth are slightly recurved and without or with a minimally expanded brownish crown; cusps only slightly compressed and blunt, with a moderately narrow cusp gap; neck moderately slender. Outer tooth row of upper jaw with 21–57 teeth, of lower jaw with 17–51 teeth (only counted for specimens from 50.8–143.3 mm SL); larger specimens have incrementally more teeth. One (rarely in lower jaw) to four inner upper and lower jaw tooth rows with small tricuspid teeth.

Lower pharyngeal bone of six paratypes (SAIAB 208051, 118.0– 122.9 mm SL; ZSM 43079, 109.3– 130.1 mm SL; ZSM 44438, 106.3 mm SL) about as wide as long (width of lower pharyngeal jawbone 95 to 103 % of pharyngeal-jaw length; Fig. 5 ). Dentigerous area of lower pharyngeal bone about 0.6 to 0.7 times length of lower pharyngeal bone length, with 21–30 teeth along posterior margin of dentigerous area. Teeth in sagittal series 7–11, molariform. Lateral anterior pharyngeal teeth bevelled to pronounced to moderately slender; those of posterior row larger than anterior ones, bevelled (minor cusp not well developed). Largest teeth (excluding molariform teeth of sagittal series) are located centrally in posterior tooth row whereas smallest teeth are found in the posterior corners of dentigerous area.

Gill rakers. Total gill rakers 13–17 with 2–4 epibranchials, one in angle (rarely two), and 9–12 ceratobranchial rakers. Anteriormost ceratobranchial gill rakers smallest. Gill rakers slender to broad and unifid, sometimes of anvil shape to bifid towards cartilaginous plug, increasing in size towards cartilaginous plug at angle. Gill raker on cartilaginous plug slightly shorter or as long as longest ceratobranchial gill raker; unifid epibranchial gill rakers slightly decreasing in size and more slender than ceratobranchial gill rakers.

Fins. Dorsal fin with 14–15 spines and 10–12 rays. First dorsal-fin spine shortest. Dorsal-fin base length between 51.2–57.3 % SL. Posterior end of dorsal fin reaching caudal fin base or ending slightly before (females) or reaching behind caudal-fin base (adult males); posterior tip of anal fin reaching caudal-fin base or ending slightly before. Caudal fin outline rounded to subtruncate and composed of 26–30 rays (16 principal caudal-fin rays and 10–14 procurrent caudal-fin rays). Anal fin with 3 spines (3 rd spine longest) and 7–9 rays. Anal-fin base length between 16.0–20.6 % SL. Pectoral fin with 13–16 rays. Pectoral-fin length between 19.1–27.9 % SL; longest pectoral ray (4 th or 5 th ray counted from dorsal margin) ending slightly before level of anus. Pelvic fin with one spine and 5 rays. Pelvic fin base slightly further (approximately 1.5–2 times flank scale width) posterior of pectoral fin base. Longest pelvic-fin ray ending behind anterior origin of anal fin base (especially in males) or ending slightly before (especially in females); adult males with moderately elongated 1 st pelvic fin ray.

Axial skeleton. Vertebral column with 27–29 (rarely 30) total vertebrae (excluding urostyle), with 14–15 abdominal vertebrae and 13–15 caudal vertebrae. Pterygiophore supporting last dorsal-fin spine inserted between neural spines 13 th and 14 th vertebra (counted from anterior to posterior) or 14 th and 15 th vertebra. Pterygiophore supporting last anal-fin spine inserted between ribs of 15 th vertebra and haemal spine of 16 th vertebra or between haemal spines of 15 th and 16 th vertebrae (rarely between haemal spines of 16 th and 17 th vertebrae). One predorsal bone (= supraneural bone) present. Hypuralia 1 + 2 and hypuralia 3 + 4 always fused into single, sutureless unit.

Coloration in life (based on field photographs of adult specimens). Pronounced sexual colour dimorphism present. Sexually mature males with characteristic coloration pattern of metallic greenish to turquoise flanks and caudal peduncle, lower lip whitish with turquoise to greenish gleam and deep black pelvic fins (see Fig. 3 ).

Body ground coloration olive; dorsum olive to pale brownish, flank and caudal peduncle greenish to turquoise. Most flank and caudal peduncle scales with greenish metallic gleam, limited to posterodorsal scale margin, and continuous with neighbouring upper and lower scale; resulting pattern giving impression of shiny oblique bars across flank. Flank scales posterior of head (first one to two rows) and chest golden to greenish. Ventral part of chest blackish (some scales with greenish gleam), belly whitish to beige. In large adult males a greyish midlateral band can be present, but mostly faint and hardly visible; between 7 and 9 light greyish vertical bars, but mostly faint or completely absent. No distinct caudal fin spot. Iris brownish with whitish patches. Dorsal head surface and ethmoidal area olive to brownish. Cheek olive with greenish to golden gleam, preoperculum golden. Operculum with golden-orange to greenish gleam, blackish opercular spot present but might be overlain by a metallic gleam. A faint greyish lachrymal stripe present. Upper lip olive with greenish gleam, lower lip whitish with turquoise to greenish gleam (especially at corner of mouth). Branchiostegal membrane greyish to turquoise. Dorsal fin membrane olive to brownish; dorsal fin lappets of spinous part deep black (first four spines with largest fin lappets), black dorsal fin lappets delineated by a narrow reddish submarginal band from the fifth dorsal fin spine. Soft rayed part of dorsal-fin membrane with small transparent to whitish maculae organized in loose oblique rows. Anal fin membrane olive to brownish (whitish to hyaline distally), with irregularly set transparent to whitish maculae; orange Pseudocrenilabrus blotch on posterior margin soft rayed part anal fin, proximal side outlined with narrow whitish band. Caudal fin membrane olive to yellowish; becoming less intensively coloured towards margin, with loosely set vertical rows of transparent to whitish maculae. Pectoral fin membrane transparent, pectoral fin rays olive. Pelvic fin membrane blackish.

Females ( Fig. 4 ) less colourful, without prominent green, gold or turquoise gleam. Body primary coloration grey to olive. Flank, caudal peduncle and chest with silvery gleam. Chest and belly white to beige. No midlateral band visible, 7 to 9 light greyish vertical bars, but mostly faint. Iris brown with whitish patches. Cheek silvery. Operculum silvery with patches of golden gleam; opercular spot black with gold metallic gleam. A faint grey lachrymal stripe. Lips white to grey. Branchiostegal membrane white to grey. Dorsal fin membrane as in males. Anal fin yellowish, without transparent or white maculae and without Pseudocrenilabrus blotch. Pectoral fins transparent, pectoral fin rays yellow to olive. Caudal fin and pelvic fin membrane yellowish.

Juvenile coloration in life. No information about juvenile coloration available.

Coloration in alcohol. Pigmentation and melanin patterns similar to live specimens, but due the preservation specimens lost original coloration, rendering especially melanin patterns more intense than in live specimens. Overall body coloration brownish. Chest in females white to beige, in males comparatively dark. Operculum grey to brown; opercular spot dark brown to black. Branchiostegal membrane dusky in males and beige in females. Large adult males with a faint brownish midlateral band along the horizontal line, vertical bars appear to be missing; females and small males either with or without any visible melanin pattern on flank, or with 6 to 9 faint vertical bars; vertical bars in subadult individuals (<40.5 mm SL) more pronounced. Dorsal fin membrane grey to brown, dorsal fin lappets blackish. Anal fin brown to grey with transparent maculae; Pseudocrenilabrus blotch whitish or faded; anal fin of females greyish. Pelvic fin blackish in males and beige to greyish in females.

Distribution and biology. Palaeoplex palimpsest is known from the Luongo River, a tributary of Luapula River, and from several locations in the Kalungwishi River drainage, which drains into Lake Mweru (Luapula drainage). At the type locality, the Luongo River is rocky with sandy to muddy patches, about 25 m wide, and with an estimated depth of approx. 1.5 m. Its shoreline is fringed with dense vegetation (reeds and small trees).

The species seems to prefer stretches of slow flowing water as it was neither observed nor collected in the small rapid-like stretches of the river close to the type locality. No stomach contents were examined, but in X-ray pictures approximately half of the investigated specimens had guts almost entirely filled with a dense fine-grained material, most likely sand, whereas in one specimen fragments of snail shells were visible in the x-rays. The molariform teeth of the lower pharyngeal jaw suggest that this species feeds at least partly on molluscs which are crushed by the pharyngeal jaws.

Etymology. A palimpsest is a parchment manuscript page, most commonly used in medieval times, that has been secondarily overwritten after layers of old handwritten letters had been scraped off, sometimes repeatedly. In many palimpsests the old letters are still visible in the background, because they had not been completely removed. The species name palimpsest is used here to denote that the palaeoplex of the new species (see etymology of genus name Palaeoplex gen. nov. above) is like a palimpsest: it is the result of the history of the species endemic to a dynamic landscape, where, e.g., recent changes in landscape and/or in ecological conditions have affected gene flow and have left genetic signatures by overwriting the genome several times, whereas remnants of more ancient genomic signatures still persist in the background of the endemic species. The contrasting hypotheses regarding the phylogenetic position of the new species, either based on nuclear DNA ( Weiss et al. 2015) or on mtDNA ( Schedel et al. 2019), are likely the result of these kinds of events that have affected the genome of Palaeoplex palimpsest gen. nov. sp. nov. The idea of referring to the genome as a palimpsest is based on Cotterill & de Wit (2011). A noun in apposition.

Figures

FIGURE 2. PCA scatter plots based on 23 meristic values; species score limits visualized as convex hulls. PC I vs PC II for all examined specimens (N = 203). PC I explain 37.53 % of the variance and PC II explains 12.17 %.

FIGURE 3. Palaeoplex palimpsest sp. nov. A. holotype, alive B. holotype (ZSM 47492), 143.3 mm SL; Zambia, Luongo River C. radiograph of holotype

FIGURE 4. Female and type locality of Palaeoplex palimpsest sp. nov. A. female paratype alive B. same individual (ZSM 44438, ID: DRC-2012-/3649, 85.3 mm SL) C. Type locality of Pa. palimpsest, Luongo River (21.09.2015, Fenton P. D. Cotterill)

FIGURE 5. Pharyngeal jaws and overview of oral jaws of Paleoplex palimpsest sp. nov. A. Lateral view of the lower pharyngeal jaw of Pa. palimpsest sp. nov. (Paratype; ZSM 43077, 122.9 mm SL) B. Dorsal view of the same lower pharyngeal jaw C. Arrangement and morphology of the oral jaw teeth (Paratype, ZSM 43079, ID: P-AA-936, 133.8 mm SL).

Tables

TABLE 3. Measurements and counts for holotype, paratypes and additional specimens of Palaeoplex palimpsest sp. nov.

Measurements	holotype	holotype + paratypes (Luongo River)				Additional material (Kalungwishi River)
		min	max	Mean±SD	N	min	max	Mean±SD
Total length (mm)	176.6	42.2	176.6	107.8 ± 37.7	34	68.3	152	109.5 ± 21.7	16
Standard length SL (mm)	143.4	33.2	143.4	86.8 ± 31.5	34	53.9	118.9	88.2 ± 17.7	16
Head length HL (mm)	45.9	11.3	45.9	27.7 ± 9.7	34	18.3	40	28.8 ± 5.5	16
% HL
Interorbital width	25.7	21.1	28.3	24.7 ± 1.8	34	21.6	27.0	24.4 ± 1.7	16
Preorbital width	31.1	25.0	34.5	29.7 ± 2.6	34	27.3	34.6	30.4 ± 1.7	16
Horizontal eye length	21.3	21.1	32.8	26.0 ± 3.4	34	21.7	30.2	26.0 ± 2.1	16
Snout length	34.6	25.2	38.7	33.9 ± 3.0	34	32.8	39.9	36.0 ± 2.0	16
Internostril distance	18.3	15.4	20.4	18.2 ± 1.3	34	16.2	22.2	19.2 ± 1.5	16
Cheek depth	31.9	17.2	31.9	24.7 ± 4.0	34	20.6	29.6	25.4 ± 2.2	16
Upper lip length	27.8	21.0	30.7	24.1 ± 2.6	34	21.8	29.2	25.2 ± 2.0	16
Lower lip length	31.2	20.8	34.0	26.7 ± 3.2	34	25.9	31.4	28.3 ± 1.5	16
Lower lip width	32.6	19.8	32.6	25.3 ± 3.3	34	20.6	33.0	25.6 ± 3.0	16
Lower jaw length	36.0	31.5	44.0	36.2 ± 2.3	34	34.7	40.2	36.5 ± 1.4	16
Lower pharyngeal jaw length	-	28.8–33.1		-	6		26.8–33.8	-	3
Lower pharyngeal jaw width	-	28.0–32.4		-	6		28.3–32.8	-	3
Width of dentigerous area of Lower	-	21.1–23.7		-	6		20.6–24.5	-	3
pharyngeal jaw % SL
Predorsal distance	34.8	32.4	38.2	35.4 ± 1.3	34	33.9	37.8	36.5 ± 0.9	16
Dorsal fin base length	56.6	51.2	57.3	54.7 ± 1.5	34	50.0	57.0	54.2 ± 1.7	16
Last dorsal fin spine length	15.2	14.9	18.5	16.6 ± 1.1	34	14.7	18.6	17.0 ± 0.9	16
Anal fin base length	20.6	16.0	20.6	18.4 ± 1.0	34	16.9	19.6	18.3 ± 0.8	16
Third anal fin spine length	11.8	11.8	19.6	15.9 ± 2.0	34	14.5	19.3	16.9 ± 1.5	16
Pelvic fin length	31.8	19.8	31.8	25.5 ± 2.5	34	23.3	29.7	24.7 ± 3.7	16
Pectoral fin length	26.2	19.1	27.9	25.3 ± 1.7	34	23.8	29.1	26.4 ± 1.4	16
Caudal peduncle depth	12.0	9.7	13.9	11.3 ± 0.8	34	10.2	11.8	11.1 ± 0.4	16
Caudal peduncle length	17.5	16.0	19.3	17.8 ± 0.7	34	16.8	19.3	17.9 ± 0.6	16
Body depth (pelvic fin base)	35.1	28.8	36.0	33.3 ± 2.1	34	30.8	35.7	33.2 ± 1.4	16
Preanal length	62.4	58.8	64.9	61.4 ± 1.4	34	58.4	62.7	61.1 ± 1.1	16