Palaeoplex, 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 : 200-201

Palaeoplex new genus

Type species: Palaeoplex palimpsest sp. nov.

Diagnosis. Palaeoplex gen. nov belongs to the megadiverse cichlid lineage of haplotilapiines (sensu Schliewen & Stiassny 2003) characterised by tricuspid teeth in the inner tooth rows of the oral jaws. Within the haplotilapiines it belongs to the still weakly defined tribe Haplochromini , which is generally characterized by the combination of following characters: basioccipital forming together with parasphenoid the apophysis of the upper pharyngeal bones, type A infraorbitals (sensu Takahashi, 2003a), bicuspid outer and tricuspid inner teeth on both jaws, ctenoid scales on flanks, and by being maternal mouthbrooders ( Poll 1986, Eccles & Trewavas 1989, Takahashi 2003b). Within Haplochromini , Palaeoplex gen. nov. is placed within the Pseudocrenilabrus group (including Lufubuchromis gen. nov., Pseudocrenilabrus , Orthochromis machadoi and Haplochromis moeruensis ) by the presence of a Pseudocrenilabrus blotch at the distal end of the anal fin in adult males, a placement which is supported also by genetic analyses. The currently monotypic genus Palaeoplex is characterized by a unique combination of the following characters: (1) a fully developed infraorbital series without a distinct gap between the lachrymal and the second infraorbital bone (in some cases the pore of the laterosensory tubule of both bones appears to be shared) (see Fig. 9 ); (2) fused hypuralia 1+2 and hypuralia 3+4 and (3) molariform teeth on sagittal series of the lower pharyngeal jaw (see Fig. 5 ). Finally, the new genus is characterised by (4) a large maximum size of up to 143.4 mm SL.

Palaeoplex is distinguished from all members of Pseudocrenilabrus and from Haplochromis moeruensis by having no distinct gap between the lachrymal and second infraorbital bone (vs. distinct gap always present, varying from narrow to very wide). In addition, the infraorbital series of Palaeoplex palimpsest is composed of the lachrymal bone (first infraorbital bone), four infraorbital bones and in some cases the dermosphenotic element (sixth infraorbital bone), hereby contrasting with Pseudocrenilabrus , where a trend towards the reduction of the infraorbital series can be observed including various combinations of fusion and loss of entire infraorbital bones (see Fig. 9 , see also Greenwood 1989).

The genus Palaeoplex with its single species Pa. palimpsest differs from Pseudocrenilabrus multicolor by having more abdominal vertebrae 14–15 vs. 13 and more scales on the horizontal line 28–31 vs. 26–27; from Ps. nicholsi by having more scales on the horizontal line 28–31 vs. 25–26, more total gill rakers 12–17 vs. 10–11, more abdominal vertebrae 14–15 vs. 12–13 and total vertebrae 27–30 vs. 25–26; from Ps. pyrrhocaudalis by having more abdominal vertebrae 14–15 vs. 12–3. It is distinguished form Ps. philander philander (populations from type locality and the Orange river drainage, South Africa) by more abdominal vertebrae 14–15 vs. 12–13; it is distinguished from Ps. philander dispersus and from several examined Pseudocrenilabrus populations of yet undefined taxonomic status (i.e. Ps. sp. “Lufira”, Ps. sp. “Lunzua”, Ps. sp. “ Botswana ”, Ps. sp. “Kalungwishi”, Ps. sp. “Luongo”, Ps. sp. “Mukuleshi) by having more abdominal vertebrae 14–15 vs. 13; in addition Palaeoplex palimpsest has more scales on the horizontal line 28–31 vs. 26–27 than Ps. philander dispersus , and from the putatively new species Pseudocrenilabrus sp. “Upper Kalungwishi” it is distinguished by having more total vertebrae 27–30 vs. 26.

From Orthochromis machadoi it is distinguished by having comparatively large scales on the chest (vs. partly scaleless chest, with deeply embedded minute scales); moreover, Palaeoplex palimpsest is distinguished from O. machadoi by having a distinctively longer last dorsal fin spine (14.7–18.6 vs. 10.1–14.6% SL), fewer dorsal fin spines (14–15 vs. 16–17) and by the position of the pterygiophore supporting last dorsal-fin spine at vertebral count: 13–14 vs. 15–16.

Palaeoplex palimpsest is distinguished from the Northern Zambian Orthochromis sensu Weiss et al. 2015 ( O. kalungwishiensis , O. luongoensis , O. katumbii , and O. mporokoso ) by having fewer dorsal fins spines (14–15 vs. 16–19) and by the position of the pterygiophore supporting the last dorsal-fin spine (vertebral count: 13–14 vs. 15–18) and by having fewer total vertebrae albeit with overlap (27–30 vs. 30–33). Further, Palaeoplex palimpsest is distinguished from the Northern Zambian Orthochromis by having comparatively large and well-developed scales on belly and chest (vs. small to minute scales, sometimes with deeply embedded chest scales, in the Northern Zambian Orthochromis ). Further, adult males of Palaeoplex palimpsest feature a large orange Pseudocrenilabrus blotch at the distal end of the anal fin which is absent in the Northern Zambian Orthochromis .

Palaeoplex differs from Lufubuchromis gen. nov. by having longer dorsal-fin spines (length of last dorsal fin spine: 14.7–18.6 vs. 10.9–14.2 % SL), by higher total gill raker counts (12–17 vs. 10–12), and by a difference in the coloration (e.g. Lufubuchromis with Pseudocrenilabrus blotch in both sexes vs. only present in males of Palaeoplex palimpsest ) and in maximum size (143.4 vs. 93.2 mm).

Etymology. The genus name Palaeoplex alludes to the concept of geoecodynamics where the palaeoplex of a species is the proxy for the total genomic variation of a given species comprising DNA signatures of the evolutionary history of a species in a given landscape (Cotteril & de Wit 2011). The analysis of the palaeoplex of a species theoretically allows for reconstruction of the species history in that landscape. As the new genus is tied geographically to a very ancient landscape, and, as published DNA analyses suggest, a long history of this genus in that landscape (e.g. Weiss et al. 2015, Schedel et al. 2019, unpublished data), the genus name refers to the scientific potential of this genus to elucidate the complex landscape evolution of that region through the analysis of the palaeoplex of the new genus. Gender masculine.

Included species. Palaeoplex palimpsest sp. nov.

Figures

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).

FIGURE 9. Overview of snout and infraorbital area of different taxa of the Pseudocrenilabrus group and related taxa. Where applicable, the gap between the lachrymal and 2nd infraorbital bone is indicated by red arrows, i.e. not in Pseudocrenilabrus multicolor as the infraorbital series of this species appears to be highly reduced. A. Paleoplex palimpsest sp. nov. (Paratype, ZSM 44438, ID: DRC-2012/3683, 81.9 mm SL, no gap between lachrymal and 2nd infraorbital bone present) B. Lufubuchromis relictus sp. nov. (Paratype, ZSM 44312, ID: DRC-2012/3249, 50.0 mm SL, no gap between lachrymal and 2nd infraorbital bone present) C. Pseudocrenilabrus multicolor (ZSM 40011, ID: Nr. 1, 46.0 mm SL) D. Pseudocrenilabrus philander (ZSM 40918, 58.9 mm SL) E. Pseudocrenilabrus nicholsi (ZSM 47140, ID: Nr. 1, 46.2 mm SL) F. Pseudocrenilabrus pyyrochaudalis (Paratype, MRAC-A7-034-P-0238-0247; ID: Nr.5, 64.2 mm SL) G. Orthochromis machadoi (BMNH 1984.2.6.104-108, ID: Nr. 1, 51.9 mm SL) H. Haplochromis moeruensis (Syntype, MRAC 216-222, ID: Nr. 222, 48.4 mm SL).