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Abstract
The Zambezi grunter,

Parauchenoglanis ngamensis

, is currently distributed across four (sub)basins in southern and south-central Africa, namely the Okavango, upper Zambezi, Kwanza, and Kasai. The present study used a combination of molecular (barcoding), colour pattern, and other morphological data to explore the possible existence of hidden species diversity within this species. Based on the available samples, analyses of molecular data uncovered seven well-supported (.96–1.00 Bayesian posterior probabilities) candidate species, with 1.6%−8.5% genetic divergence between them. These, in addition to two more candidate species without genetic data, exhibited a combination of consistent colour pattern and other morphological differences that supported their distinction. The present study redescribes P. ngamensis, which is confined to the Okavango and upper Zambezi (sub)basins, and describes eight new species: two from the Kwanza Basin and six from the Kasai sub-basin. The fact that some of the species occur allopatrically, whereas others are sympatric and even syntopic indicates the complex palaeogeographical history of these basins. In addition, the high species diversity discovered in the Kasai sub-basin seems to be related to its highly peculiar hydrography. Accurate delimitation of species boundaries and mapping of their distribution is crucial for conservation assessments and guiding their protection.

Parauchenoglanis

• 1a. Humeral process broadly triangular .... 2
  • 1b. Humeral process pointed .... (12)
• 2a. Humeral process embedded under the skin; anterior margin of the pectoral-fin spine mostly serrated ....
  Parauchenoglanis zebratus
  • 2b. Humeral process clearly visible through the skin; anterior margin of the pectoral-fin spine mostly smooth .... 3
• 3a. Rounded caudal fin (Fig. 4A) .... 4
  • 3b. Truncated caudal fin (Fig. 4B) .... 7
• 4a. Long barbels, external mandibular barbel reaching beyond distal tip of pectoral spine; total vertebrae count <30 ....
  Parauchenoglanis stiassnyae
  • 4b. Short barbels, external mandibular barbel never reaching beyond the distal tip of pectoral; total vertebrae count ≥32 .... 5
• 5a. Head and fins with numerous black spots at all sizes (22.8 - 204.2 mm SL); body of medium- to large-sized specimens (>50.0 mm SL) with numerous spots, with some of them forming five to seven (median six) vertical rows and with other black spots situated in between those rows (Fig. 5) ....
  Parauchenoglanis ngamensis
  • 5b. Head and fins with few black spots or spots entirely absent at all sizes (32.1 - 223.0 mm SL); body of medium- to large-sized specimens (>100 mm SL) with black spots forming only five to six (median six, rarely seven) vertical rows and with no other spots situated in between these rows .... 6
• 6a. Head moderately depressed (head depth 48.5% - 54.0% HL); deeper body depth, 15.5% - 21.4% SL (Fig. 11) ....
  Parauchenoglanis patersoni
  • 6b. Head highly depressed (head depth 34.6% - 40.0% HL); shallower body depth, 11.6% - 14.0% SL (Fig. ....
    Parauchenoglanis dolichorhinus
• 7a. Snout round or partly round; body with vertical rows of black blotches; head with black blotches .... 8
  • 7b. Snout bluntly triangular; body with black spots; head sometimes also with black spots .... 9
• 8a. Vertical rows of black blotches extending onto adipose fin; blotches along the lateral line smaller than the eye size; eyes situated dorsally, i.e. high on the head, towards its upper surface (Fig. 12) ....
  Parauchenoglanis ernstswartzi
  • 8b. Vertical rows of black blotches not extending onto adipose fin; blotches along the lateral line larger than the eye size; eyes clearly situated dorsolaterally (Fig. 13) ....
    Parauchenoglanis megalasma
• 9a. Head and fins with black spots; black spots present in between vertical rows of spots; external mandibular barbel not reaching the distal tip of pectoral-fin spine, when adpressed along the body .... 10
  • 9b. Head and fins without black spots or with faint black spots only; absence of black spots in between vertical rows of spots; external mandibular barbel reaching the distal tip of pectoral-fin spine, when adpressed along the body .... 11
• 10a. Mandibular barbels unspotted; only one or two black spots in between vertical rows of black spots; long predorsal length, 39.4% - 42.0% SL (Fig. 10) ....
  Parauchenoglanis lueleensis
  • 10b. Mandibular barbels spotted; more than two black spots in between vertical rows of black spots; short predorsal length, 38.4% - 39.2% SL (Fig. 11) ....
    Parauchenoglanis poikilos
• 11a. Fins unspotted; high adipose fin height (Fig. 14) ....
  Parauchenoglanis luendaensis
  • 11b. Fins with faint black spots; low adipose fin height (Fig. 15) ....
    Parauchenoglanis chiumbeensis
• 12a. Anterior margin of the pectoral-fin spine completely serrated .... 13
  • 12b. Anterior margin of the pectoral-fin spine only partly and slightly serrated, or smoothly serrated .... 15
• 13a. Caudal peduncle relatively long as high ....
  Parauchenoglanis buettikoferi
  • 13b. Caudal peduncle shorter than high .... 14
• 14a. Barbels long, with external mandibular barbel reaching beyond distal tip of pectoral-fin spine; colour pattern with 6 - 10 (rarely 11) vertical rows of spots ....
  Parauchenoglanis punctatus
  • 14b. Barbels short, with external mandibular barbel not reaching beyond distal tip of pectoral spine; colour pattern with five to seven bands ....
    Parauchenoglanis monkei
• 15a. Preorbital head length greater than maximum head depth (measured at level of supraoccipital process); numerous small black spots on both head and fins .... 16
  • 15b. Preorbital head length less than maximum head depth; colour pattern of body and fins variable, but not as above .... 17
• 16a. Interorbital distance 28% - 30% HL; spots on head and flanks of equal size ....
  Parauchenoglanis longiceps
  • 16b. Interorbital distance 22% - 25% HL; spots on head smaller than those on flanks ....
    Parauchenoglanis pantherinus
• 17a. Adipose and dorsal fins high (adipose fin height, 5% - 8% SL; dorsal fin height, 19% - 30% SL); colour pattern on flank faint, one horizontal row of two to six large spots, being as large as or larger than the eye diameter, visible on the level of lateral line ....
  Parauchenoglanis altipinnis
  • 17b. Adipose and dorsal fins shallower (adipose fin height, 3% - 7% SL; dorsal fin height, 15% - 25% SL); colour pattern of body and fins variable but not as above .... 18
• 18a. Barbels long, with external mandibular barbel reaching distal tip of pectoral spine (minimum one-third HL); whole body covered with spots of equal size ....
  Parauchenoglanis ahli
  • 18b. Barbels short, with external mandibular barbel never reaching beyond distal tip of pectoral spine (shorter than one-third HL); whole body covered with spots of different sizes, arranged in horizontal and/or vertical rows ....
    Parauchenoglanis balayi